Search

The unique bacterial infection microenvironment (IME) usually requires complicated design of nanomaterials to adapt to IME for enhancing antibacterial therapy. Here, an alternative IME adaptative nitrite reductase-mimicking nanozyme is constructed by in situ growth of ultrasmall copper sulfide clusters on the surface of a nanofibrillar lysozyme assembly (NFLA/CuS NHs), which can temporally regulate nitric oxide (NO) gradient concentration to kill bacteria initially and promote tissue regeneration subsequently. Benefiting from a copper nitrite reductase (CuNIR)-inspired structure with CuS cluster as active center and NFLA as skeleton, NFLA/CuS NHs efficiently boost the catalytic reduction of nitrite to NO. The inherent supramolecular fibrillar networks displays excellent bacterial capture capability, facilitating initial high-concentration NO attacks on the bacteria. The subsequent catalytic release of low-concentration NO by NFLA/CuS NHs-mediated nitrite reduction remarkably promotes cell migration and angiogenesis. This work paves the way for dynamically eliminating MDR bacterial infection and promoting tissue regeneration in a simple and smart way through CuNIR-mimicking catalysis. [ABSTRACT FROM AUTHOR]

Denitrification is a crucial process in the global nitrogen cycle, in which two functionally equivalent genes, nirS and nirK, catalyse the critical reaction and are usually used as marker genes. The nirK gene can function independently, whereas nirS requires additional genes to encode nitrite reductase and is more sensitive to environmental factors than nirK. However, the ecological differentiation mechanisms of those denitrifying microbial communities and their adaptation strategies to environmental stresses remain unclear. Here, we conducted metagenomic analysis for sediments and bioreactor samples from Lake Donghu, China. We found that nirS‐type denitrifying communities had a significantly lower horizontal gene transfer frequency than that of nirK‐type denitrifying communities, and nirS gene phylogeny was more congruent with taxonomy than that of nirK gene. Metabolic reconstruction of metagenome‐assembled genomes further revealed that nirS‐type denitrifying communities have robust metabolic systems for energy conservation, enabling them to survive under environmental stresses. Nevertheless, nirK‐type denitrifying communities seemed to adapt to oxygen‐limited environments with the ability to utilize various carbon and nitrogen compounds. Thus, this study provides novel insights into the ecological differentiation mechanism of nirS and nirK‐type denitrifying communities, as well as the regulation of the global nitrogen cycle and greenhouse gas emissions. [ABSTRACT FROM AUTHOR]

Partial denitrification granular sludge (PDGS) can provide long-term stable nitrite for anaerobic ammonia oxidation (anammox). The cultivation of ordinary activated sludge from wastewater treatment plants into PDGS can further promote the application of PD in practical engineering. In this study, the feasibility of fast start-up of PDGS was explored by inoculating waste sludge in up-flow anaerobic sludge blanket (UASB) reactor with synergistic control of nitrogen load rate (NLR, 0.05–0.65 kg N/m3/d) and electron donor starvation (EDS) (240–168 mg L−1), and system performance, particle characteristics and microbial structure were studied. The results showed that PD-UASB started successfully within 48 days, the average nitrite accumulation rate (NTR) and nitrate removal ratio (NRR) reached 79.6% and 82.5% after successful initiation, accompanied by high abundance of PD bacteria (Thauera, Pseudomonas, unclassflied commamonadaceae and Limnobacter) (25.3%). The increase of PD activity, and the difference between nitrate reductase (NAR) and nitrite reductase (NIR) contributed to nitrite production. Besides, the sludge shifted from flocculated (≤0.5 mm, 95.37%) to granulated state (0.5–2 mm, 64.74%), which could be due to the increase of extracellular polymers (EPS) (especially T-EPS) and metabolism of specific microorganisms (Bacteroidota and Chloroflexi, 19.92%). Good sludge granulation promoted the settleability of PD (the SVI5 was 47.248 mL/ g. ss after successful start-up). In summary, good PD sludge granulation process could be achieved in a short time by synergistically controlling NLR and EDS. [ABSTRACT FROM AUTHOR]

Soil acidification is a global environmental problem with significant impacts on agricultural production, environmental protection, and ecosystem health. Soil acidification is widespread in China, affecting crop yields, agricultural product quality, and biodiversity. Since the 1980s, much work has been done on acidic soils in China, but it is controversial whether excessive nitrogen fertilizer application can lead to soil acidification mechanisms. To address the above issues, we conducted a meta-analysis of 115 published papers to integrate and analyze the effects of N fertilizer application on soil acidification and biological properties from 1980 to 2024. We also quantified the effect of nitrogen fertilization on soil acidification and biological changes under different climatic conditions. The results showed that under long-term application of nitrogen fertilizers in China from 1980 to 2024, soil pH decreased by an average of 15.27%, and the activities of soil urease, nitrate reductase, nitrite reductase, catalase, glutamate dehydrogenase, and glutamate synthetase decreased by an average of 9.82–22.37%. The soil microbial community richness (Chao1 index) increased by 6.53%, but the community diversity (Shannon index) decreased by 15.42%. Among the dominant soil microorganisms, the relative abundance of bacteria decreased by an average of 9.67–29.38% and the abundance of gene expression of nifH, amoA-AOA, amoA-AOB, and qnorB decreased by 9.92–19.83%. In addition, we found that the mean annual temperature and rainfall impacted soil acidification via their effect on soil microbial diversity and community composition. This study provides a scientific basis for an in-depth understanding of the spatial and temporal variation of soil acidification and biological properties in China. [ABSTRACT FROM AUTHOR]

Cenchrus fungigraminus is a new species and is largely used as forage and mushroom substrate. However, it can usually not be planted on farmland on account of local agricultural land policy. Interplanting Cenchrus fungigraminus with other crops annually (short-term) is an innovative strategy to promote the sustainable development of the grass industry in southern China. To further investigate this, C. fungigraminus mono-planting (MC), C. fungigraminus–potato interplanting (CIP) and C. fungigraminus–broad bean interplanting (CIB) were performed. Compared to MC, soil microbial biomass carbon (SMBC), soil organic matter (SOM), ammoniacal nitrogen (AMN), pH and soil amino sugars had a positive effect on the rhizosphere soil of CIP and CIB, as well as enhancing soil nitrogenase, nitrite reductase, and peroxidase activities (p < 0.05). Moreover, CIP improved the root vitality (2.08 times) and crude protein (1.11 times). In addition, CIB enhanced the crude fiber of C. fungigraminus seedlings. These two interplanting models also improved the microbial composition and diversity (Actinobacteria, Firmicutes, and Bacteroidota, etc.) in the rhizosphere soil of C. fungigraminus seedlings. Among all the samples, 189 and 59 genes were involved in methane cycling and nitrogen cycling, respectively, which improved the presence of the serine cycle, ribulose monophosphate, assimilatory nitrate reduction, methane absorption, and glutamate synthesis and inhibited denitrification. Through correlation analysis and the Mantel test, the putative functional genes, encoding functions in both nitrogen and methane cycling, were shown to have a significant positive effect on pH, moisture, AMN, SOM, SMBC, and soil peroxidase activity, while not displaying a significant effect on soil nitrogenase activity and total amino sugar (p < 0.05). The short-term influence of the interplanting model was shown to improve land use efficiency and economic profitability per unit land area, and the models could provide sustainable agricultural production for rural revitalization. [ABSTRACT FROM AUTHOR]

Microbial communities are fundamental components driving critical biogeochemical carbon (C), nitrogen (N) and sulfur (S) cycles in groundwater ecosystems. The reduction–oxidation (redox) potential is one important environmental factor influencing the microbial community composition. Here, we developed a bio-trap method using in-situ sediment as a matrix to collect aquifer sediment samples and evaluate the response of microbial composition and C/N/S cycling functions to redox variations created by providing sole O2, joint O2 and H2, and sole H2 to three wells. Illumina sequencing analyses showed that the microbial communities in the bio-trap sediment could respond quickly to redox changes in the wells, demonstrating that this bio-trap method is promising for detecting microbial variation in the aquifer sediment. The microbial metabolic functions related to C, N and S cyclings and organic pollutants degradation were predicted by the Kyoto Encyclopedia of Genes and Genomes (KEGG) approach. It was found that the joint O2 and H2 injection produced medium oxidation–reduction potential (ORP −346 and −614 mV) and enhanced more microbial functions than sole O2 or H2, which mainly include oxidative phosphorylation, most carbon source metabolism, various pollutants degradation, and nitrogen and sulfur metabolism. Moreover, the functional genes encoding phenol monooxygenase, dioxygenase, nitrogen fixation, nitrification, aerobic and anaerobic nitrate reductase, nitrite reductase, nitric oxide reductase, and sulfur oxidation increased. These findings tell us the contaminant bioremediation and N, S metabolism can be promoted by adjusting ORP realised by injecting joint O2 and H2. [ABSTRACT FROM AUTHOR]

Cupriavidus necator, despite lacking direct electron transfer capabilities, demonstrates efficient reduction of various redox mediators in oxygen‐free cultivation within bioelectrochemical systems. This study investigates the reduction site of ferricyanide through inhibition and expression rate analysis of oxygen and nitrate respiration chain complexes, comparing aerobic cultivation conditions with fructose as carbon and electron donor to autotrophic (CO2/H2/O2) and anodic cultivation conditions (fructose/anode). Azide inhibition identified cytochrome c oxidase as the primary complex facilitating electron transfer to ferricyanide, with a secondary role proposed for nitrite reductase NirS, demonstrating a 3.9±1.1‐fold higher expression when exposed to anodic conditions. The 2.9±0.6‐fold increase in the expression of the natural porin OmpA under anodic conditions implies its potential involvement in ferricyanide uptake. Additionally, chemically permeabilizing cell membranes with cetyltrimethylammonium bromide doubles ferricyanide reduction rates without an anode present, offering insights for optimizing redox mediation in C. necator based bioelectrochemical systems. This study opens up new possibilities for the targeted optimization of mediated electron transfer in C. necator and other organisms. [ABSTRACT FROM AUTHOR]

Heterotrophic nitrification-aerobic denitrification (HN-AD) bacteria are the key functional microorganisms needed to achieve simultaneous nitrification and denitrification (SND). In this study, 25 strains of HN-AD bacteria were successfully isolated from a stable landfill leachate biochemical treatment system, of which 10 strains belonged to Firmicutes and 15 strains belonged to Proteobacteria. Bacillus subtilis F4 and Alcaligenes faecalis P4 displayed good tolerance at a wide range of ammonia nitrogen (NH4+-N) concentrations. When the C/N ratio was 20, the removal rates of ammonia nitrogen were 90.1% and 89.5%, and the chemical oxygen demand (COD) removal rates were 92.4% and 93.9%, respectively. The napA gene encoding periplasmic nitrate reductase (Nap) and the nirS gene encoding nitrite reductase (Nir) were detected, and nitrogen balance showed assimilation and HN-AD was the main nitrogen metabolism mode in both strains. The use of immobilization materials could increase removal rate of ammonia nitrogen by 21.1% and 29.6%, respectively. The research results of this work can provide theoretical basis and technical support for the practical application of HN-AD bacteria to enhance the treatment of high ammonia nitrogen wastewater with high efficiency and low consumption. [ABSTRACT FROM AUTHOR]

Human mitochondria contain a molybdoprotein capable of reducing amidoximes using cytochrome b5/cytochrome b5 reductase (Cb/CbR). This 'amidoxime reducing component' (ARC) also reduces nitrite to nitric oxide (NO). In the plant kingdom, distinct functions have been suggested for ARCs. Thus, the single ARC of Chlamydomonas reinhardtii (crARC) reduces nitrite to NO by taking electrons from nitrate reductase (NR). Therefore, it was proposed that a dual NR/crARC system can generate NO under physiological conditions and the crARC was renamed to 'NO‐forming nitrite reductase' (NOFNiR). In contrast to this, the two ARC enzymes from Arabidopsis thaliana were not found to produce NO in vitro at physiological nitrite concentrations, suggesting a different, as yet unknown, function in vascular plants. Here, we have investigated the two ARCs of Lotus japonicus (LjARCs) to shed light on this controversy and to examine, for the first time, the distribution of ARCs in plant tissues. The LjARCs are localized in the cytosol and their activities and catalytic efficiencies, which are much higher than those of A. thaliana, are consistent with a role as NOFNiR. LjARCs are prone to S‐nitrosylation in vitro by S‐nitrosoglutathione and this post‐translational modification drastically inhibits their activities. The enzymes are mainly expressed in flowers, seeds and pods, but are absent in nodules. LjARCs are active with NR and Cb/CbR as electron‐transferring systems. However, the LjNR mRNA levels in seeds and pods are negligible, whereas our proteomic analyses show that pods contain the two ARCs, Cb and CbR. We conclude that LjARCs may play a role as NOFNiR by receiving electrons from the Cb/CbR system but do not act in combination with NR. [ABSTRACT FROM AUTHOR]

AbstractThis work was conducted to evaluate the effect of N source (NH4+/NO3-) and the implication of NH4+-induced acidification on plant development in Arabidopsis thaliana. seedlings were hydroponically cultivated during 21 days under three ratios of NO3−/NH4+ (mM); 2.5/0.0; 1.25/1.25, and 0.0/2.5. For each ratio, plants were cultivated under not controlled pH and adjusted pH at 6.2. Ammonium-fed plants (0.0/2.5) showed chlorosis if cultivated under uncontrolled pH. This symptom was associated with suppressions in plant growth, chlorophyll and iron contents as well as shoots hydration and nutrient concentration. Growth was limited with increasing NH4+ medium-concentration. At pH 6.2, plants receiving only NH4+ produced the same biomass as NO3-fed ones. The mineral disturbances in plants grown on strictly NH4+-medium (0.0/2.5) were alleviated under controlled pH. The activities of nitrate reductase (NR) and nitrite reductase (NIR) were lower in plants amended only with NH4+ under uncontrolled pH. At adjusted pH, the NR activity was ameliorated but that of NIR was not ameliorated, suggesting hence that NR activity depended on medium pH but that of NIR was related only to the pool of NO2-. In conclusion, this work demonstrated that the adjustment of pH at 6.2 mitigated significantly the toxic effects of ammonium to A. thaliana. [ABSTRACT FROM AUTHOR]

In the soils of vanadium (V) smelters, a diverse array of microorganisms relies on metabolic activities for survival amid stress. However, the characteristics and functions of soil microbiomes in V mining environments remain unexplored on a continental scale. This study thoroughly investigates the microbial diversity, community assembly, and functional potential of soil microbiome across 90 V smelters in China. Alpha diversity decreases significantly along the V gradient, with V emerging as the primary factor influencing community structure, followed by other environmental, climatic, and geographic factors. The null model reveals that V induces homogeneous selection, shaping co‐occurrence patterns and leading to increased number of positive associations, particularly with keystone genera such as f_Gemmatimonadaceae, Nocardioides, Micromonospora, and Rubrobacter under higher V concentrations (>559.6 mg/kg). Moreover, a metagenomic analysis yields 67 metagenome‐assembled genomes, unraveling the potential metabolic pathways of keystone taxa and their likely involvement in the V(V) reduction process. Nitrate and nitrite reductase (nirK, narG), and mtrABC are found to be taxonomically affiliated with Micromonospora. sp, FEN‐1250. sp, Nocardioides. sp, etc. Additionally, the reverse citric acid cycle (rTCA) likely serves as the primary carbon fixation pathway, synthesizing alternative energy for putative V reducers, highlighting a potentially synergistic relationship between autotrophic and heterotrophic processes that supports microbial survival. Our findings comprehensively uncover the driving forces behind soil community variation under V stress, revealing robust strategies possibly employed by indigenous microorganisms to mitigate the impact of V. These insights hold potential for applications in bioremediation. Plain Language Summary: Vanadium, a byproduct of anthropogenic smelting, is predominantly sequestered in the soil, where soil microorganisms act as vital indicators of ecosystem health under pollutant exposure. The soil layer not only functions as a primary repository but also provides buffering capacity, impeding the migration of vanadium into groundwater. Study results reveal that the occurrence and abundance of microorganisms are collectively influenced by vanadium levels, environmental factors, geographical location, and climatic conditions. Species distribution is shaped by the interplay of vanadium levels and microbial migration across geographic gradients. In heavily contaminated soil, microbial interdependence is markedly heightened, especially with vanadium‐tolerant species, compared with relatively healthy soil, supporting diverse nutrient utilization for microbial growth. Keystone taxa in the community network assume pivotal roles in nutrient cycling, energy synthesis, and governing the bioreduction of high‐valent vanadium. These activities may mitigate the impact of vanadium on the soil environment near smelter sites. Key Points: Vanadium, environmental parameters, climatic, and geographic factors jointly explained the community variationElevated vanadium content promoted deterministic community assembling processes and strengthened the interspecific microbial associationKeystone taxa facilitated community survival via both putative autotrophic and heterotrophic pathways [ABSTRACT FROM AUTHOR]

The unique positioning of mangrove ecosystems between land and sea makes them vital in the nitrogen cycle. The role of nitrification in the nitrogen cycle is important to provide nitrogen compounds readily absorbed by mangrove plants. Nevertheless, the nitrification process and nitrifying bacteria in mangrove areas have yet to be comprehensively understood. The primary objective of this study is to provide comprehensive analysis of nitrifying bacteria in mangrove sediments by conducting a systematic review. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses method is used as a guide to help report reviews systematically and has a flow chart to show the process of selecting relevant studies. Data collection was carried out by utilizing 6 databases and journal search engines including Scopus, PubMed, ResearchGate, Google Scholar, and Springer in order to achieve more comprehensive findings. This study employed the widely recognized and commonly used technique of defining the review's scope in a focused manner by first identifying the population, intervention, comparison, and outcome. This study identified 358 studies, and 31 studies were included in the review after screening. Based on the screening results, research on nitrifying bacteria in mangrove sediments is geographically limited to several countries such as Indonesia, Vietnam, Thailand, China, Mexico, the United States, India, and Saudi Arabia. This study vealed that there is a high level of diversity among nitrifying bacteria in mangrove sediment, with five distinct groups identified: ammonia oxidizing bacteria, nitrite oxidizing bacteria, anammox bacteria, and comammox bacteria, a recently identified group. In carrying out changes in nitrogen compounds, nitrifying bacteria use functional genes from different steps of the nitrification process, such as nitrogenase, ammonia monooxygenase subunit A, nitrite oxidoreductase alpha subunit, nitrate reductase alpha chain, nitrite reductase, nitric oxide reductase, nitrous oxide reductase, hydrazine synthase, hydrazine oxidoreductase and hydroxylamine oxidoreductase genes. Ammonia-oxidizing bacteria were the predominant group in general, but various nitrifying bacteria groups were distributed diversely across different mangrove environments. This study also indicated the vegetation type and the distribution of nitrifying bacteria in mangrove sediments. The depth of these sediments typically varies from 0 to 60 centimeters, with most samples taken at a depth of 0 to 20 centimeters. The type of vegetation at the sampling location is dominated by species of Kandelia candel, Avicennia marina, Kandelia obovata, and Rhizophora mangle. Limitations regarding research on nitrifying bacteria in mangrove sediments provide opportunities for in-depth study. This comprehensive review provides an in-depth overview of the variety and spread of nitrifying bacteria, highlighting their role in nitrogen cycling and emphasizing the potential for discovering new nitrifying bacteria in mangrove sediments. [ABSTRACT FROM AUTHOR]

Background: To better understand the influence of habitat on the genetic content of bacteria, with a focus on members of Candidate Phyla Radiation (CPR) bacteria, we studied the effects of transitioning from soil via seepage waters to groundwater on genomic composition of ultra-small Parcubacteria, the dominating CPR class in seepage waters, using genome resolved metagenomics. Results: Bacterial metagenome-assembled genomes (MAGs), (318 total, 32 of Parcubacteria) were generated from seepage waters and compared directly to groundwater counterparts. The estimated average genome sizes of members of major phyla Proteobacteria, Bacteroidota and Cand. Patescibacteria (Candidate Phyla Radiation – CPR bacteria) were significantly higher in soil-seepage water as compared to their groundwater counterparts. Seepage water Parcubacteria (Paceibacteria) exhibited 1.18-fold greater mean genome size and 2-fold lower mean proportion of pseudogenes than those in groundwater. Bacteroidota and Proteobacteria also showed a similar trend of reduced genomes in groundwater compared to seepage. While exploring gene loss and adaptive gains in closely related CPR lineages in groundwater, we identified a membrane protein, and a lipoglycopeptide resistance gene unique to a seepage Parcubacterium genome. A nitrite reductase gene was also identified and was unique to the groundwater Parcubacteria genomes, likely acquired from other planktonic microbes via horizontal gene transfer. Conclusions: Overall, our data suggest that bacteria in seepage waters, including ultra-small Parcubacteria, have significantly larger genomes and higher metabolic enrichment than their groundwater counterparts, highlighting possible genome streamlining of the latter in response to habitat selection in an oligotrophic environment. [ABSTRACT FROM AUTHOR]

Mycobacterium abscessus (Mab) is an opportunistic pathogen afflicting individuals with underlying lung disease such as Cystic Fibrosis (CF) or immunodeficiencies. Current treatment strategies for Mab infections are limited by its inherent antibiotic resistance and limited drug access to Mab in its in vivo niches resulting in poor cure rates of 30-50%. Mab's ability to survive within macrophages, granulomas and the mucus laden airways of the CF lung requires adaptation via transcriptional remodeling to counteract stresses like hypoxia, increased levels of nitrate, nitrite, and reactive nitrogen intermediates. Mycobacterium tuberculosis (Mtb) is known to coordinate hypoxic adaptation via induction of respiratory nitrate assimilation through the nitrate reductase narGHJI. Mab, on the other hand, does not encode a respiratory nitrate reductase. In addition, our recent study of the transcriptional responses of Mab to hypoxia revealed marked down-regulation of a locus containing putative nitrate assimilation genes, including the orphan response regulator nnaR (nitrate/nitrite assimilation regulator). These putative nitrate assimilation genes, narK3 (nitrate/nitrite transporter), nirBD (nitrite reductase), nnaR, and sirB (ferrochelatase) are arranged contiguously while nasN (assimilatory nitrate reductase identified in this work) is encoded in a different locus. Absence of a respiratory nitrate reductase in Mab and down-regulation of nitrogen metabolism genes in hypoxia suggest interplay between hypoxia adaptation and nitrate assimilation are distinct from what was previously documented in Mtb. The mechanisms used by Mab to fine-tune the transcriptional regulation of nitrogen metabolism in the context of stresses e.g. hypoxia, particularly the role of NnaR, remain poorly understood. To evaluate the role of NnaR in nitrate metabolism we constructed a Mab nnaR knockout strain (MabΔnnaR) and complement (MabΔnnaR+C) to investigate transcriptional regulation and phenotypes. qRT-PCR revealed NnaR is necessary for regulating nitrate and nitrite reductases along with a putative nitrate transporter. Loss of NnaR compromised the ability of Mab to assimilate nitrate or nitrite as sole nitrogen sources highlighting its necessity. This work provides the first insights into the role of Mab NnaR setting a foundation for futurework investigating NnaR's contribution to pathogenesis. [ABSTRACT FROM AUTHOR]

Rural drainage ditches serve as important sinks for heavy metals and antibiotics. However, the combined effects of heavy metals and antibiotics on ecological processes and functions in ditches remain unclear. We studied the combined effects of cadmium and doxycycline on nitrification, denitrification, anaerobic ammonia oxidation, and nitrous oxide emission rates in constructed ditch wetlands during 84 days. Results show that combined pollution decreased denitrification and anaerobic ammonia oxidation rates, but increased nitrous oxide production rates. The addition of either cadmium or doxycycline decreased the glucokinase and glyceraldehyde-3-phosphate dehydrogenase activities, and their combined pollution had a higher impact on adenosine triphosphate than on nicotinamide adenine dinucleotide. Moreover, the activities of the electron transport system, nitrate reductase, and nitrite reductase were enhanced by short-term pollutant exposure, but inhibited by long-term pollutant exposure. Structural equation modelling further revealed that electron production and transport impacted the rates of denitrification, anaerobic ammonia oxidation, and nitrous oxide production directly and indirectly by changing the activities of nitrate and nitrite reductases. [ABSTRACT FROM AUTHOR]

The present investigation was conducted to explore the role of potassium nutrition in improving biomass and physio-chemical alterations to reduce the adverse effects of salinity in mungbean. A sand-culture experiment was carried out under different salinity levels (0, 50, and 100 mM NaCl) with two levels of potassium (0 and 50 mM K2SO4) and two mungbean cultivars (NM-92 and Ramzan), and the alterations in mungbean biomass and metabolic activities were investigated. The results suggested that salinity significantly reduced the biomass, nitrate reductase activity (NRA), nitrite reductase activity (NiRA), total soluble proteins, chlorophyll a, chlorophyll b, total chlorophyll, nitrogen, potassium, calcium, magnesium, and phosphorous contents in both mungbean cultivars in comparison to the control. However, K2SO4 at 50 mM significantly improved all the parameters in both mungbean cultivars except for the sodium content. A significant increase in the total free amino acids, carotenoids, and sodium content in both mungbean cultivars was observed due to salt stress. Moreover, principal component analysis and heatmaps were developed individually for both mungbean cultivars to assess the variability and correlation among the studied attributes under all applied treatments. Under saline conditions, the mungbean 'Ramzan' showed more marked reductions in almost all the growth parameters as compared to 'NM-92'. The results suggest that the application of K2SO4 ameliorates the adverse effects of salinity by regulating osmolyte production, NRA, and NiRA, thus promoting plant growth and productivity. [ABSTRACT FROM AUTHOR]

Enhanced denitrification has been reported under weak electric fields. However, it is difficult to investigate the mechanism of enhanced denitrification due to the complex interspecific interactions of mixed-culture systems. In this study, Pseudomonas stutzeri, capable of denitrification under anaerobic conditions, was selected for treating low COD/N (2.0, ratio between concentration of chemical oxygen demand and NO3−-N) artificial wastewater under constant external voltages of 0.2, 0.4, and 0.6 V. The results revealed that P. stutzeri exhibited the highest efficiency in nitrate reduction at 0.2 V. Moreover, the maximum nitrate removal rate was 15.96 mg/(L·h) among the closed-circuit groups, 19.39% higher than that under the open-circuit group. Additionally, a notable reduction in nitrite accumulation was observed under weak electric fields. Enzyme activity analysis showed that the nitrate reductase activities were significantly increased among the closed-circuit groups, while nitrite reductase activities were inhibited. Transcriptomic analysis indicated that amino acid metabolism, carbohydrate metabolism, and energy metabolism were increased, enhancing the resistance of P. stutzeri to environmental stress and the efficiency of carbon source utilization for denitrification. The current study examined the impacts of weak electric fields on enzyme activities and microbial metabolic pathways and offers valuable insights into the mechanism by which denitrification is enhanced by weak electric fields. [ABSTRACT FROM AUTHOR]

Introduction: Nitric oxide (NO) is a vasodilator gas that plays a critical role in mitochondrial respiration and skeletal muscle function. NO is endogenously generated by NO synthases: neuronal NO synthase (nNOS), endothelial NO synthase (eNOS), or inducible NO synthase (iNOS). NO in skeletal muscle is partly generated by nNOS, and nNOS deficiency can contribute to muscular dystrophic diseases. However, we and others discovered an alternative nitrate/nitrite reductive pathway for NO generation: nitrate to nitrite to NO. We hypothesized that nitrate supplementation would increase nitrate accumulation in skeletal muscle and promote a nitrate/nitrite reductive pathway for NO production to compensate for the loss of nNOS in skeletal muscle. Methods: Wild-type (WT) and genetic nNOS knockout (nNOS-/-) mice were fed normal chow (386.9 nmol/g nitrate) and subjected to three treatments: highnitrate water (1 g/L sodium nitrate for 7 days), low-nitrate diet (46.8 nmol/g nitrate for 7 days), and low-nitrate diet followed by high-nitrate water for 7 days each. Results: High-nitrate water supplementation exhibited a greater and more significant increase in nitrate levels in skeletal muscle and blood in nNOS-/- mice than in WT mice. A low-nitrate diet decreased blood nitrate and nitrite levels in both WT and nNOS-/- mice. WT and nNOS-/- mice, treated with low-nitrate diet, followed by high-nitrate water supplementation, showed a significant increase in nitrate levels in skeletal muscle and blood, analogous to the increases observed in nNOS-/- mice supplemented with high-nitrate water. In skeletal muscle of nNOS-/- mice on high-nitrate water supplementation, on low-nitrate diet, and in low-high nitrate treatment, the loss of nNOS resulted in a corresponding increase in the expression of nitrate/nitrite reductive pathway-associated nitrate transporters [sialin and chloride channel 1 (CLC1)] and nitrate/ nitrite reductase [xanthine oxidoreductase (XOR)] but did not show a compensatory increase in iNOS or eNOS protein and eNOS activation activity [p-eNOS (Ser1177)]. Discussion: These findings suggest that a greater increase in nitrate levels in skeletal muscle of nNOS-/- mice on nitrate supplementation results from reductive processes to increase NO production with the loss of nNOS in skeletal muscle. [ABSTRACT FROM AUTHOR]

Drought stress is one of the main environmental factors limiting plant growth and development. Plants adapt to changing soil moisture by modifying root architecture, inducing stomatal closure, and inhibiting shoot growth. The AP2/ERF transcription factor DREB2A plays a key role in maintaining plant growth in response to drought stress, but the molecular mechanism underlying this process remains to be elucidated. Here, it was found that overexpression of MdDREB2A positively regulated nitrogen utilisation by interacting with DRE cis‐elements of the MdNIR1 promoter. Meanwhile, MdDREB2A could also directly bind to the promoter of MdSWEET12, which may enhance root development and nitrogen assimilation, ultimately promoting plant growth. Overall, this regulatory mechanism provides an idea for plants in coordinating with drought tolerance and nitrogen assimilation to maintain optimal plant growth and development under drought stress. Summary statement: In this study, it was found that MdDREB2A positively regulated nitrogen utilisation by interacting with the promoter of the nitrite reductase gene MdNIR1. Meanwhile, MdDREB2A could also promote MdSWEET12‐modulated carbon translocation from shoot to root, further promoting plant growth. [ABSTRACT FROM AUTHOR]

The present study examined the regulatory mechanism of hydrogen sulfide (H2S) and nitric oxide (NO) in nickel (Ni) stressed cyanobacteria viz., Nostoc muscorum and Anabaena sp. by analyzing growth, photosynthetic pigments, biochemical components (protein and carbohydrate), exopolysaccharides (EPS), inorganic nitrogen content, and activity of enzymes comprised in nitrogen metabolism and Ni accumulation. The 1 µM Ni substantially diminished growth by 18% and 22% in N. muscorum and Anabaena sp. respectively, along with declining the pigment contents (Chl a/Car ratio and phycobiliproteins), and biochemical components. It also exerted negative impacts on inorganic uptake of nitrate and nitrite contents; nitrate reductase and nitrite reductase; and ammonium assimilating enzymes (glutamine synthetase, glutamate synthase, and glutamate dehydrogenase exhibited a reverse trend) activities. Nonetheless, the adverse impact of Ni can be mitigated through the exogenous supplementation of NaHS [sodium hydrosulfide (8 µM); H2S donor] and SNP [sodium nitroprusside (10 µM); NO donor] which showed substantial improvement on growth, pigments, nitrogen metabolism, and EPS layer and noticeably occurred as a consequence of a substantial reduction in Ni accumulation content which minimized the toxicity effects. The accumulation of Ni on both the cyanobacterial cell surface (EPS layer) are confirmed by the SEM–EDX analysis. Further, the addition of NO scavenger (PTIO; 20 µM) and inhibitor of NO (L-NAME; 100 µM); and H2S scavenger (HT; 20 µM) and H2S inhibitor (PAG; 50 µM) reversed the positive responses of H2S and NO and damages were more prominent under Ni stress thereby, suggesting the downstream signaling of H2S on NO-mediated alleviation. Thus, this study concludes the crosstalk mechanism of H2S and NO in the mitigation of Ni-induced toxicity in rice field cyanobacteria. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Bioprocess Engineering is the property of Chinese Journal of Bioprocess Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Chinese Journal of Oil Crop Sciences is the property of Oil Crops Research Institute of Chinese Academy of Agricultural Sciences and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Introduction:Nitrogen (N) deposition seriously affects the function of carbon (C) and N cycling in terrestrial ecosystems by altering soil microbial communities, especially in desert steppe ecosystems. However, there is a need for a comprehensive understanding of how microorganisms involved in each C and N cycle process respond to N deposition. Methods: In this study, shotgun metagenome sequencing was used to investigate variations in soil C and N cycling-related genes in the desert steppe in northern China after 6 years of the following N deposition: N0 (control); N30 (N addition 30 kg ha-1 year-1): N50 (N addition 50 kg ha-1 year-1). Results: N deposition significantly increased the relative abundance of Actinobacteria (P < 0.05) while significantly decreased the relative abundances of Proteobacteria and Acidobacteria (P < 0.05). This significantly impacted the microbial community composition in desert steppe soils. The annual addition or deposition of 50 kg ha-1 year-1 for up to 6 years did not affect the C cycle gene abundance but changed the C cycle-related microorganism community structure. The process of the N cycle in the desert steppe was affected by N deposition (50 kg ha-1 year-1), which increased the abundance of the pmoAamoA gene related to nitrification and the nirB gene associated with assimilation nitrite reductase. There may be a niche overlap between microorganisms involved in the same C and N cycling processes. Discussion: This study provides new insights into the effects of N deposition on soil microbial communities and functions in desert steppe and a better understanding of the ecological consequences of anthropogenic N addition. [ABSTRACT FROM AUTHOR]

Despite the well-known individual roles of potassium (K+) and jasmonic acid (JA) in plant responses to various stresses, their combined effects on improving tolerance to metalloid arsenate (AsV) toxicity and their influence on physiological and biochemical mechanisms remain largely unexplored. Therefore, the present study was conducted to explore the concomitant role of K+ and JA in nitrogen (N) and sulfur (S) metabolisms and regulation of antioxidant system in tomato seedlings under AsV toxicity conditions. The obtained data reveal that K+ and/or JA boosted the tolerance of tomato (Solanum lycopersicum L.) seedlings to AsV toxicity. However, the effect of a combined dose of K+ and JA was found to be more efficient as compared to the alone application. Seedlings subjected to AsV exhibited suppressed morphological attributes (shoot and root length, shoot and root fresh weight, and shoot and root dry weight), and physio-biochemical characteristics. Also, AsV-treated tomato seedlings showed enhanced reactive oxygen species (ROS) and increased the activity of ROS-producing enzymes (O 2 •— -generating NADPH oxidase activity and H 2 O 2 -generating glycolate oxidase] and also a chlorophyll (Chl) degrading enzyme [chlorophyllase (Chlase) activity]. However, the exogenous supply of K+ and JA synergistically inhibited Chl degradation and overproduction of ROS by suppressing their responsible enzymes activity. Moreover, it induced gas exchange parameters and activity of enzymes responsible for the photosynthesis process (carbonic anhydrase and Rubisco), Chl biosynthesis (δ -aminolevulinic acid dehydratase), and suppressed Chlase activity, and overproduction of ROS and their producing enzymes activity. Most interestingly, the combined application of K+ and JA substantially increased N and S content and their assimilation by upregulating the activity of enzymes involved in these key pathways (nitrate reductase, nitrite reductase, glutamine synthetase, glutamate synthase, ATP sulfurylase, adenosine 5-phosphosulfate reductase, O -acetylserine (thiol) lyase and sulfide reductase). The obtained results strongly reveal that the combined application of K+ and JA improved tolerance of tomato seedlings to AsV toxicity by enhancing N and S assimilation pathways and antioxidant system. [Display omitted] • AsV toxicity impaired n and s assimilation pathways in tomato seedlings. • AsV stress inhibited chl and Cys-biosynthesis and enhances overproduction of ROS. • K + plus JA enhanced n and s assimilation pathways under AsV toxicity conditions. • K + plus JA improved chl and Cys-biosynthesis in AsV stressed-tomato seedlings. • K + plus JA suppressed ROS overproduction and increased antioxidant system. [ABSTRACT FROM AUTHOR]

Enhancing Nitrogen Use Efficiency (NUE) is extremely important towards mitigating climate change, especially in wheat where the NUE is less than 50%. Hence, optimizing grain yield under reduced application of nitrogenous fertilizer is a significant challenge. To address this challenge, a comprehensive study was conducted to investigate various agronomic traits and morphological, biochemical and molecular parameters related to NUE. This study explored their interrelationships and effects on grain yield, providing novel insights that were not previously reported. A set of 278 diverse wheat genotypes were assessed, encompassing eight NUE‐related field traits. All traits' values were reduced under stressed N (ranging from 7.5% to 77.5%) except Nitrogen Utilization Efficiency (NUtE) and NUE. Data analysis showed a significant positive correlation between grain yield and all other NUE‐related traits (r2 value ranged from.23 to 1.00), highlighting their relevance in comprehending the biological NUE of wheat plants. Principal component analysis (PCA) also revealed that N at head and N at harvest were more connected with gain yield, NUE and biomass under the optimum N condition, but less connected with gain yield and NUE under the stressed N condition. To complement the field data, representative genotypes were further subjected to a hydroponics experiment under absolute N control to study the different morphological parameters, photosynthetic pigments and the performance of essential N‐ and C‐metabolizing enzymes at the seedling stage. N stress had a detrimental impact on the majority of the parameters (−0.84% to −79.8%). Nitrite reductase (NiR), glutamate dehydrogenase (GDH) and isocitrate dehydrogenase (ICDH) enzymes as well as root length (RL), root fresh weight (RFW) and CS transcript, were positively affected by 5.9%–35.6%. The correlation analysis highlighted the substantial influence of four key N‐metabolizing enzymes, namely nitrate reductase (NR), glutamine synthetase (GS), glutamate oxo‐glutarate aminotransferase (GOGAT), and GDH on grain yield. Additionally, this study highlighted the direct and indirect associations between seedling parameters and field traits, where shoot and root length were found to be most significant for N acquisition, especially under N stress. In conclusion, these findings offer valuable insights into the intricate network of traits and parameters influencing wheat grain yield under varying N regimes. [ABSTRACT FROM AUTHOR]

The generation of nitrite by the oral microbiota is believed to contribute to healthy cardiovascular function, with oral nitrate reduction to nitrite associated with systemic blood pressure regulation. There is the potential to manipulate the composition or activities of the oral microbiota to a higher nitrate-reducing state through nitrate supplementation. The current study examined microbial community composition and enzymatic responses to nitrate supplementation in sessile oral microbiota grown in continuous culture. Nitrate reductase (NaR) activity and nitrite concentrations were not significantly different to tongue-derived inocula in model biofilms. These were generally dominated by Streptococcus spp., initially, and a single nitrate supplementation resulted in the increased relative abundance of the nitrate-reducing genera Veillonella, Neisseria, and Proteus spp. Nitrite concentrations increased concomitantly and continued to increase throughout oral microbiota development. Continuous nitrate supplementation, over a 7-day period, was similarly associated with an elevated abundance of nitratereducing taxa and increased nitrite concentration in the perfusate. In experiments in which the models were established in continuous low or high nitrate environments, there was an initial elevation in nitrate reductase, and nitrite concentrations reached a relatively constant concentration over time similar to the acute nitrate challenge with a similar expansion of Veillonella and Neisseria. In summary, we have investigated nitrate metabolism in continuous culture oral biofilms, showing that nitrate addition increases nitrate reductase activity and nitrite concentrations in oral microbiota with the expansion of putatively NaR-producing taxa. IMPORTANCE Clinical evidence suggests that blood pressure regulation can be promoted by nitrite generated through the reduction of supplemental dietary nitrate by the oral microbiota. We have utilized oral microbiota models to investigate the mechanisms responsible, demonstrating that nitrate addition increases nitrate reductase activity and nitrite concentrations in oral microbiota with the expansion of nitrate-reducing taxa. [ABSTRACT FROM AUTHOR]

Introduction: An appropriate supply of ammonium (NH4+) in addition to nitrate (NO3-) can greatly improve plant growth and promote maize productivity. However, knowledge gaps exist regarding the mechanisms by which different nitrogen (N) fertilizer sources affect the enzymatic activity of nitrogen metabolism and non-structural carbohydrates during the post-anthesis period. Methods: A field experiment across 3-year was carried out to explore the effects of four nitrateammonium ratio (NO3-/NH4+ = 1:0 (N1), 1:1 (N2), 1:3 (N3), and 3:1 (N4)) on postanthesis dry matter (DM) and N accumulation, partitioning, transportation, and grain yield in maize. Results: NO3-/NH4+ ratio with 3:1 improved the enzymatic activity of N metabolism and non-structural carbohydrate accumulation, which strongly promoted the transfer of DM and N in vegetative organs to reproductive organs and improved the pre-anthesis DM and nitrogen translocation efficiency. The enzymatic activities of nitrate reductase, nitrite reductase, glutamine synthetase, glutamine oxoglutarate aminotransferase, and nonstructural carbohydrate accumulation under N4 treatment were increased by 9.30%-32.82%, 13.19%-37.94%, 4.11%-16.00%, 11.19%-30.82%, and 14.89%-31.71% compared with the other treatments. Mixed NO3--N and NH4+-N increased the total DM accumulation at the anthesis and maturity stages, simultaneously decreasing the DM partitioning of stem, increasing total DM, DM translocation efficiency (DMtE), and contribution of pre-anthesis assimilates to the grain (CAPG) in 2015 and 2017, promoting the transfer of DM from stem to grain. Furthermore, the grain yield increased by 3.31%-9.94% (2015), 68.6%-26.30% (2016), and 8.292%-36.08% (2017) under the N4 treatment compared to the N1, N2, and N3 treatments. Conclusion: The study showed that a NO3-/NH4+ ratio of 3:1 is recommended for high-yield and sustainable maize management strategies in Northwestern China. [ABSTRACT FROM AUTHOR]

Nonsymbiotic phytoglobins (nsHbs) are a diverse superfamily of hemoproteins grouped into three different classes (1, 2, and 3) based on their sequences. Class 1 Hb are expressed under hypoxia, osmotic stress, and/or nitric oxide exposure, while class 2 Hb are induced by cold stress and cytokinins. Both are mainly six-coordinated. The deoxygenated forms of the class 1 and 2 nsHbs from A. thaliana (AtHb1 and AtHb2) are able to reduce nitrite to nitric oxide via a mechanism analogous to other known globins. NsHbs provide a viable pH-dependent pathway for NO generation during severe hypoxia via nitrite reductase-like activity with higher rate constants compared to mammalian globins. These high kinetic parameters, along with the relatively high concentrations of nitrite present during hypoxia, suggest that plant hemoglobins could indeed serve as anaerobic nitrite reductases in vivo. The third class of nsHb, also known as truncated hemoglobins, have a compact 2/2 structure and are pentacoordinated, and their exact physiological role remains mostly unknown. To date, no reports are available on the nitrite reductase activity of the truncated AtHb3. In the present work, three representative nsHbs of the plant model Arabidopsis thaliana are presented, and their nitrite reductase-like activity and involvement in nitrosative stress is discussed. The reaction kinetics and mechanism of nitrite reduction by nsHbs (deoxy and oxy form) at different pHs were studied by means of UV-Vis spectrophotometry, along with EPR spectroscopy. The reduction of nitrite requires an electron supply, and it is favored in acidic conditions. This reaction is critically affected by molecular oxygen, since oxyAtHb will catalyze nitric oxide deoxygenation. The process displays unique autocatalytic kinetics with metAtHb and nitrate as end-products for AtHb1 and AtHb2 but not for the truncated one, in contrast with mammalian globins. [ABSTRACT FROM AUTHOR]

Light intensity plays a critical regulatory role in determining plant yield and quality, and energy consumption in plant factory with artificial light (PFAL). The effects of different light intensities (200, 300, 400, 500, and 600 µmol·m−2·s−1) of light-emitting diodes (LED) red and blue light with ratio 4:1 on growth, quality, nitrogen and amino acid metabolisms of ryegrass were investigated. The results showed the tiller number and shoot fresh weight in ryegrass were increased, while plant height and stem diameter remained stable with the improvement of light intensity. The highest levels of soluble protein, free amino acid, and DPPH free radical clearance rate in photon flux density (PPFD) at 500 µmol·m−2·s−1, and then significantly decreased with light intensity increased. The highest soluble sugar content was found at PPFD of 600 µmol·m−2·s−1, while malondialdehyde (MDA) content remained stable in all treatments. As the light intensity increased, nitrate content decreased, while nitrate reductase (NR) activity and the ammonium content increased. As light intensity was increased from 200 to 600 µmol·m−2·s−1, nitrite reductase (NiR) activity first decreased and then increased. Moreover, glutamate and cysteine contents increased first and then decreased, while glutamate synthase (GOGAT), glutamine synthase (GS), glutamate dehydrogenase (GDH), and cysteine synthases (CS) activities increased continuously with light intensity. Light intensity was significantly correlated with the parameters of growth, quality, nitrogen and amino acid metabolisms in ryegrass. It was recommended that PPFD at 400–500 µmol·m−2·s−1, photoperiod of 16 h/d was suitable for ryegrass high-efficient production in PFAL with relatively low energy cost. [ABSTRACT FROM AUTHOR]

• The nosZ gene of N 2 O reductase determined by paddy soil tillage state. • The clade Ⅱ and Ⅰ nosZ gene was dominated in the tillage and fallow period, respectively. • Heavy-metal pollution inhibited the N 2 O emission while not affecting the genes' switch. • The genus Bradyhizobium most significantly regulated the N 2 O flux. Paddy soils are an important source of atmospheric nitrous oxide (N 2 O). However, numerous studies have focused on N 2 O production during the soil tillage period, neglecting the N 2 O production during the dry fallow period. In this study, we conducted an incubation experiment using the acetylene inhibition technique to investigate N 2 O emission and reduction rates of paddy soil profiles (0-1 m) from Guangdong Province and Jinlin Province in China, with different heavy-metal pollution levels. The abundance and community structures of denitrifying bacteria were determined via quantitative -PCR and Illumina MiSeq sequencing of nosZ, nirK , and nirS genes. Our results showed that the potential N 2 O emission rate, N 2 O production rate, and denitrification rate have decreased with increasing soil vertical depth and heavy-metal pollution. More importantly, we found that the functional gene type of N 2 O reductase switched with the tillage state of paddy soils, which clade Ⅱ nosZ genes were the dominant gene during the tillage period, while clade Ⅰ nosZ genes were the dominant gene during the dry fallow period. The heavy-metal pollution has less effect on the niche differentiation of the nosZ gene. The N 2 O emission rate was significantly regulated by the genus Bradyhizobium , which contains both N 2 O reductase and nitrite reductase genes. Our findings suggests that the nosZ gene of N 2 O reductase can significantly impact the N 2 O emission from paddy soils. [Display omitted] [ABSTRACT FROM AUTHOR]

Cushion plants are one kind of unique specie in alpine ecosystems. They have a compact perennial cushion structure and play a role in facilitating the survival of other associated species by improving the local micro-environment. They are called "engineers" in the alpine ecosystem and their enhancement of soil nutrient availability is one of the ways of their engineering effect. In this study, Androsace tapete, a species of cushion plant widely distributed on the Qinghai-Tibet Plateau, was selected to investigate the dynamics of this process during the growing season at elevations of 4500 m and 4800 m on the southern slope of the Nyenchenthanglha mountains in Damxung. The effects of A. tapete on soil nutrient availability were analyzed by comparing the inorganic nitrogen content, net nitrogen mineralization rate and soil enzyme activities during the growing season in the soil under A. tapete and ambient grassland (CK). The results showed three important aspects of this system. (1) Soil nitrate nitrogen and ammonium nitrogen did not show significant differences at 4500 m, but the contents of nitrate nitrogen and inorganic nitrogen under the A. tapete soil significantly increased in the middle of the growing season at 4800 m, with nitrate nitrogen increasing by 56% and inorganic nitrogen increasing by 74.5%. (2) The trend and rate of soil nitrogen mineralization were both changed under A. tapete. In the 4500 m sample site, soil net nitrogen mineralization under A. tapete was negative (nitrogen immobilization) in the middle of the growing season, and the rate was –0.11 µg g–1 d–1, while that of CK was positive (nitrogen mineralization) and the rate was 0.61 µg g–1 d–1; and the difference between them was significant. However, both were positive in the early and late growing season, and the difference did not reach a significant level. In the 4800 m sample site, the soil net nitrogen mineralization under A. tapete was positive in the early part of the growing season, and the rate was 0.07 µg g–1 d–1, while the mineralization for CK was negative, and the rate was –1.17 µg g–1 d–1; and the difference was significant. In the middle of the growing season, both of them were negative, but the soil net nitrogen mineralization rate under A. tapete (–1.95 µg g–1 d–1) was significantly lower than that of CK (–0.02 µg g–1 d–1). At the late stage of the growing season, both of them were negative, and the difference was not significant. (3) Activities of nitrate reductase and nitrite reductase in the soil were significantly increased under A. tapete. Compared to CK at the 4500 m sample site, the activities of nitrate reductase and nitrite reductase under A. tapete were increased by 9.1% and 15.7%, respectively; and they were increased by 22.5% and 16.1%, respectively, at the 4800 m sample site. The activities of these two enzymes were significantly correlated with the dynamics of inorganic nitrogen in the soil. These results indicated that, compared to CK, the cushion plant A. tapete can change the process of soil nitrogen mineralization and the content of inorganic nitrogen, but that change had seasonal dynamics and spatial differences, which implies that this process was affected not only by the engineering of the cushion plant but also by changes in the local environment. Therefore, the engineering effect of cushion plant A. tapete was not constant during the growing seasons, and further studies are needed to clarify this process, especially considering the rapidly changing climate on the Qinghai-Tibet Plateau. [ABSTRACT FROM AUTHOR]

Nitrate accumulation is a common problem in most leafy vegetables and it happens when the amount of nitrate absorption exceeds the amount consumed by the plant. This study was conducted as a factorial experiment in the form of a completely randomized design and in three replications. The first factor included adding nitrate (calcium nitrate) to Hoagland's standard solution at three levels of 0, 10 and 20%, and the second factor was adding different concentrations of molybdenum from sodium molybdate salt at four levels of 0, 0.5, 1.5 and 3 µM. The measured traits included traits of some growth characteristics, total phenol and flavonoids, ascorbic acid, spinach leaf nitrate. According to the obtained results, fresh and dry weight of leaf, dry weight of root and percentage of dry matter increased by increasing calcium nitrate concentration up to 20% and molybdenum application up to 3 µM in nutrient solution. The simultaneous application of molybdenum and nitrogen had no significant effect on total phenolic, total flavonoid and ascorbic acid traits, and the highest amount of these traits was observed in 3 µM molybdenum. The highest amount of leaf nitrate (3247.4 mg kg-1 FW) was observed in the treatment of 20% additional nitrate along with molybdenum. Based on the results, the use of molybdenum in nutrient solution had a reducing effect on nitrate accumulation in spinach leaf, therefore adding 3 µM sodium molybdate to Hoagland nutrient solution in hydroponic system for spinach production is recommended to obtain the maximum amount of antioxidant compounds and the minimum amount of nitrate accumulation. Introduction Plants take nitrogen (N) either as nitrate (NO3-) or ammonium (NH4+) form for various growth and developmental processes; however, NO3- is more important for such processes. For most of the crop plants, the nitrate form is mobile, less toxic, and can be stored in vacuoles. However, Nitrate must be reduced to NH4+ before it can be utilized for the synthesis of amino acids, proteins, and other nitrogenous compounds in plant cells. Nitrate reductase (NR) and nitrite reductase (NiR), the key nitrate assimilatory enzymes, are located in cytosol and chloroplasts and catalyze nitrate reduction to NO2- followed by NO2- to NH4+, respectively, in the leaf tissues. However, NH4+ is directly assimilated to produce different amino acids by the mutual actions of glutamine synthetase (GS) and glutamate synthase (GOGAT) enzymes in a cyclic manner within the plant cells. Nitrate accumulation is a common problem in most leafy vegetables and it happens when the amount of nitrate absorption exceeds the amount consumed by the plant. Molybdenum (Mo) is an essential microelement for higher plants and also a metal component of the Mo-cofactor, (Moco) biosynthesis. Moco binds to Mo-requiring enzymes and optimizes their activities for normal functioning of plant growth and developmental processes. Molybdenum plays a significant role in N metabolism, which includes nitrate reduction, assimilation, and fixation, by regulating the NR and GS enzymes activities and expressions. During symbiotic N fixation, Mo acts as a cofactor for nitrogenase enzymes to catalyze the redox reaction to convert elemental N into ammonium ions. Materials and methods This study was conducted as a factorial experiment in the form of a completely randomized design and in three replications. The first factor included adding nitrate (calcium nitrate) to Hoagland's standard solution at three levels of 0, 10 and 20%, and the second factor was adding different concentrations of molybdenum from sodium molybdate salt at four levels of 0, 0.5, 1.5 and 3 µM. This research was conducted in the research greenhouse of Campus of Agriculture and Natural Resources Razi University. Senator spinach seeds were obtained from Fardin Kasht Alborz Institute. Spinach seeds were disinfected with 1% sodium hypochlorite for 5 minutes and then planted in seedling trays containing cocopeat and perlite with a volume ratio of 1:1. The measured traits included traits of some growth characteristics, total phenol and flavonoids, ascorbic acid, spinach leaf nitrate. Results and discussion According to the obtained results, fresh and dry weight of leaf, dry weight of root and percentage of dry matter increased by increasing calcium nitrate concentration up to 20% and molybdenum application up to 3 µM in nutrient solution. The simultaneous application of molybdenum and nitrogen had no significant effect on total phenolic, total flavonoid and ascorbic acid traits, and the highest amount of these traits was observed in 3 µM molybdenum. The highest amount of leaf nitrate (3247.4 mg kg-1 FW) was observed in the treatment of 20% additional nitrate along with molybdenum. The most important point in this research was the use of molybdenum to control nitrate accumulation, and the use of molybdenum in concentrations of 1.5 and 3 µM was able to reduce the amount of nitrate accumulation in the aerial parts to some extent, thus neutralizing the toxicity of excess nitrate. The use of sodium molybdate can be one of the recommended ways to reduce the accumulation of nitrates and at the same time enrich molybdenum in spinach and increase the nutritional value of this plant. Conclusion Nitrate and ammonium are the major forms of N that plants use for different growth and developmental processes. The present study revealed that Mo fertilizer plays a key role in N metabolism through regulating the activities and expressions of N-assimilating enzymes. In general, the results of this research showed that the increase in molybdenum concentration in hydroponic culture affected the growth and biochemical characteristics of spinach. Based on the results, the use of molybdenum in nutrient solution had a reducing effect on nitrate accumulation in spinach leaf, therefore adding 3 µM sodium molybdate to Hoagland nutrient solution in hydroponic system for spinach production is recommended to obtain the maximum amount of antioxidant compounds and the minimum amount of nitrate accumulation. [ABSTRACT FROM AUTHOR]

This study describes the seasonal course of denitrifying and nitrate-reducing bacteria in a dimictic mesotrophic lake (Lake Scharmützelsee, Brandenburg, Germany) within a three-year period from 2011 to 2013. The bacterial cell numbers were quantified by the fluorescence microscopy, most probable number (MPN) and PCR-dependent quantification of the chromosomal 16S rDNA and of the nirS and nirK gene copy number. The highest seasonal differences (up to three orders of magnitudes) have been measured using MPN in the epilimnion. This variation was not reflected by PCR-dependent approaches or direct microscopical enumeration. At adverse conditions (low temperature and/or low nitrate concentrations), the differences between MPN and gene copy numbers increased by up to five orders of magnitudes and decreased to one magnitude at favourable environmental conditions. These results can be explained best by an increasing ratio of viable but not cultivable (VBNC) cells or dead cells at impairing conditions. In the hypolimnion, the courses of MPN and nir gene copy numbers were similar. This can be explained by a higher feeding pressure and therefore smaller amounts of dormant cells. In the pelagial in general, the total cell numbers enumerated by either microscopical or molecular approaches were similar. In the sediment, more than 99% of the DNA was obviously not related to viable bacteria but was rather DNA in dead cells or adsorbed to particle surfaces. [ABSTRACT FROM AUTHOR]

Various crop rotation patterns can result in differences in nutrient consumption and the accumulation of toxic substances in the soil, indirectly impacting the soil environment and its nutrient supply capacity. Implementing optimized crop planting practices is beneficial for maintaining the favorable physical and chemical properties of farmland soil in the arid area of northwestern China. This study aimed to establish a crop rotation pattern to improve key enzyme activities and soil nitrogen conversion efficiency, as well as understand the underlying mechanism for enhancing nitrogen supply capacity. A field experiment was conducted to study the effect of four flax planting patterns, which included 13 crop rotation patterns with different crop frequencies: 100% Flax (Cont F), 50% Flax (I) (WFPF, FPFW, PFWF, FWFP), 50% Flax (II) (FWPF, WPFF, PFFW, FFWP), 25% Flax (WPWF, PWFW, WFWP, FWPW), on the key enzyme activities and the rate of soil nitrogen conversion, as well as the nitrogen supply capacity. Here, F, P, and W represent oilseed flax, potato, and wheat, respectively. The results indicated that the wheat stubble significantly increased the intensity of soil ammonification and denitrification before planting. Additionally, the activity levels of soil nitrate reductase and nitrite reductase under wheat stubble were significantly increased by 66.67% to 104.55%, while soil urease activity significantly decreased by 27.27–133.33% under wheat stubble compared to other stubbles. After harvest, the activities of soil nitrate reductase and nitrite reductase under the wheat stubble decreased significantly, and the intensity of soil ammonification, nitrification, and denitrification reduced significantly by 7.83–27.72%. The WFWP and FWFP treatments led to a significant increase in soil nitrogen fixation intensity under various crop rotations after harvest and significantly increased the levels of inorganic nitrogen in the soil before the planting of the next crop. This study suggests that the long-term rotation planting patterns WFWP and FWFP can significantly enhance the key enzyme activities of soil nitrogen conversion and significantly improve soil nitrogen conversion before crop sowing. This may increase the rate of soil nitrogen transfer and raise the available nitrogen content of the soil. These findings are crucial for reducing soil nitrogen loss and improving soil nitrogen nutrient supply capacity in dry areas of the Loess Plateau of China. [ABSTRACT FROM AUTHOR]

Nitric oxide (NO) is synthesized in all kingdoms of life, where it plays a role in the regulation of various physiological and developmental processes. In terms of endogenous NO biology, fungi have been less well researched than mammals, plants, and bacteria. In this review, we summarize and discuss the studies to date on intracellular NO biosynthesis and function in fungi. Two mechanisms for NO biosynthesis, NO synthase (NOS)-mediated arginine oxidation and nitrate- and nitrite-reductase-mediated nitrite reduction, are the most frequently reported. Furthermore, we summarize the multifaceted functions of NO in fungi as well as its role as a signaling molecule in fungal growth regulation, development, abiotic stress, virulence regulation, and metabolism. Finally, we present potential directions for future research on fungal NO biology. [ABSTRACT FROM AUTHOR]

Microbial-driven processes, including nitrification and denitrification closely related to soil nitrous oxide (N2O) production, are orchestrated by a network of enzymes and genes such as amoA genes from ammonia-oxidizing bacteria (AOB) and archaea (AOA), narG (nitrate reductase), nirS and nirK (nitrite reductase), and nosZ (N2O reductase). However, how climatic factors and agricultural practices could influence these genes and processes and, consequently, soil N2O emissions remain unclear. In this comprehensive review, we quantitatively assessed the effects of these factors on nitrogen processes and soil N2O emissions using mega-analysis (i.e., meta-meta-analysis). The results showed that global warming increased soil nitrification and denitrification rates, leading to an overall increase in soil N2O emissions by 159.7%. Elevated CO2 stimulated both nirK and nirS with a substantial increase in soil N2O emission by 40.6%. Nitrogen fertilization amplified NH4+-N and NO3−-N contents, promoting AOB, nirS, and nirK, and caused a 153.2% increase in soil N2O emission. The application of biochar enhanced AOA, nirS, and nosZ, ultimately reducing soil N2O emission by 15.8%. Exposure to microplastics mostly stimulated the denitrification process and increased soil N2O emissions by 140.4%. These findings provide valuable insights into the mechanistic underpinnings of nitrogen processes and the microbial regulation of soil N2O emissions. [ABSTRACT FROM AUTHOR]

Cultivated peanut (Arachis hypogaea L.) represents one of the most important oil and cash crops world-widely. Unlike many other legumes, peanuts absorb nitrogen through their underground pods. Despite this unique feature, the relationship between yield and nitrogen uptake within the pod zone remains poorly understood. In our pot experiment, we divided the underground peanut part into two zones—pod and root—and investigated the physiological and agronomic traits of two peanut cultivars, SH11 (large seeds, LS) and HY23 (small seeds, SS), at 10 (S1), 20 (S2), and 30 (S3) days after gynophores penetrated the soil, with nitrogen application in the pod zone. Results indicated that nitrogen application increased pod yield, kernel protein content, and nitrogen accumulation in plants. For both LS and SS peanut cultivars, optimal nitrogen content was 60 kg·hm− 2, leading to maximum yield. LS cultivar exhibited higher yield and nitrogen accumulation increases than SS cultivar. Nitrogen application up-regulated the expression of nitrogen metabolism-related genes in the pod, including nitrate reductase (NR), nitrite reductase (NIR), glutamine synthetase (GS), glutamate synthase (NADH-GOGAT), ATP binding cassette (ABC), and nitrate transporter (NRT2). Additionally, nitrogen application increased enzyme activity in the pod, including NR, GS, and GOGAT, consistent with gene expression levels. These nitrogen metabolism traits exhibited higher up-regulations in the large-seeded cultivar than in the small-seeded one and showed a significant correlation with yield in the large-seeded cultivar at S2 and S3. Our findings offer a scientific basis for the judicious application and efficient utilization of nitrogen fertilization in peanuts, laying the groundwork for further elucidating the molecular mechanisms of peanut nitrogen utilization. [ABSTRACT FROM AUTHOR]

Trichoderma can promote plant growth under saline stress, but the mechanisms remain to be revealed. In this study, we investigate photosynthetic gas exchange, photosystem II (PSII) performance, nitrogen absorption and accumulation in a medicinal plant wolfberry (Lycium chinense) in saline soil supplemented with Trichoderma biofertilizer (TF). Larger nitrogen and biomass accumulation were found in plants supplemented with TF than with organic fertilizer (OF), suggesting that Trichoderma asperellum promoted plant growth and nitrogen accumulation under saline stress. T. asperellum strengthened root nitrogen (N) absorption according to greater increased root NH4+ and NO3− influxes under supplement with TF than OF, while nitrogen assimilative enzymes such as nitrate reductase, nitrite reductase and glutamine synthetase activities in roots and leaves were also stimulated. Thus, the elevated N accumulation derived from the induction of T. asperellum on nitrogen absorption and assimilation. Greater increased photosynthetic rate (Pn) and photosynthetic N-use efficiency under supplement with TF than OF illustrated that T. asperellum enhanced photosynthetic capacity and N utilization under saline stress. Although increased leaf stomatal conductance contributed to carbon (C) isotope fractionation under TF supplement, leaf 13C abundance was significantly increased by supplement with TF rather than OF, indicating that T. asperellum raised CO2 assimilation to a greater extent, reducing C isotope preference. Trichoderma asperellum optimized electron transport at PSII donor and acceptor sides under saline stress because of lower K and J steps in chlorophyll fluorescence transients under supplement with TF than OF. The amount of PSII active reaction centers was also increased by T. asperellum. Thus, PSII performance was upgraded, consistent with greater heightened delayed chlorophyll fluorescence transients and I1 peak under supplement with TF than OF. In summary, TF acted to increase N nutrient acquisition and photosynthetic C fixation resulting in enhanced wolfberry growth under saline soil stress. [ABSTRACT FROM AUTHOR]

While ameliorating effects of melatonin (MT) on abiotic stress tolerance in plants are widely reported, the mechanism that underlies this process remains elusive. This work investigated mechanisms by which MT improved drought tolerance in pepper (Capsicum annuum) plants. A foliar spray of 0.1 mM MT treatment was applied to plants grown at 80% and 40% of full field capacity for 3 days. Drought stress caused a significant decrease in plant dry weight, relative water content, leaf water potential, PSII efficiency (Fv/Fm ratio), chlorophyll, soluble protein, leaf and root nitrogen content. Drought increased hydrogen peroxide, malondialdehyde (MDA), nitrate, ammonium, free amino acids, soluble sugars, proline and glycine betaine. Drought also increased peroxidase (POD), glutathione S-transferase (GST) and catalase (CAT) activities, electrolyte leakage (EL) and methylglyoxal (MG). MT pre-treatment reduced oxidative stress and improved nitrogen metabolism by activating various enzymes such as nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS), glutamate synthetase (GOGAT) and glutamine dehydrogenase (GDH) activities. It also activated enzymes related to the glyoxalase system (Gly I and Gly II) and decreased NO3-, NH4+ and free amino acid content. Our study suggests a cost-effective and sustainable solution to improve crop productivity in water-limited conditions, by enhancing plant growth, photosynthesis and nitrogen content. [ABSTRACT FROM AUTHOR]

This study examined the impacts of growth stage and ensiling duration on the fermentation characteristics, nitrite content, and bacterial communities during the ensiling of alfalfa. Harvested alfalfa was divided into two groups: vegetative growth stage (VG) and late budding stage (LB). The fresh alfalfa underwent wilting until reaching approximately 65% moisture content, followed by natural fermentation. The experiment followed a completely randomized design, with samples collected after the wilting of alfalfa raw materials (MR) and on days 1, 3, 5, 7, 15, 30, and 60 of fermentation. The growth stage significantly influenced the chemical composition of alfalfa, with crude protein content being significantly higher in the vegetative growth stage alfalfa compared to that in the late budding stage (p < 0.05). Soluble carbohydrates, neutral detergent fiber, and acid detergent fiber content were significantly lower in the vegetative growth stage compared to the late budding stage (p < 0.05). Nitrite content, nitrate content, nitrite reductase activity, and nitrate reductase activity were all significantly higher in the vegetative growth stage compared to the late budding stage (p < 0.05). In terms of fermentation parameters, silage from the late budding stage exhibited superior characteristics compared to that from the vegetative growth stage. Compared to the alfalfa silage during the vegetative growth stage, the late budding stage group exhibited a higher lactate content and lower pH level. Notably, butyric acid was only detected in the silage from the vegetative growth stage group. Throughout the ensiling process, nitrite content, nitrate levels, nitrite reductase activity, and nitrate reductase activity decreased in both treatment groups. The dominant lactic acid bacteria differed between the two groups, with Enterococcus being predominant in vegetative growth stage alfalfa silage, and Weissella being predominant in late budding stage silage, transitioning to Lactiplantibacillus in the later stages of fermentation. On the 3rd day of silage fermentation, the vegetative growth stage group exhibited the highest abundance of Enterococcus, which subsequently decreased to its lowest level on the 15th day. Correlation analysis revealed that lactic acid bacteria, including Limosilactobacillus, Levilactobacillus, Loigolactobacillus, Pediococcus, Lactiplantibacillus, and Weissella, played a key role in nitrite and nitrate degradation in alfalfa silage. The presence of nitrite may be linked to Erwinia, unclassified_o__Enterobacterales, Pantoea, Exiguobacterium, Enterobacter, and Allorhizobium–Neorhizobium–Pararhizobium–Rhizobium. [ABSTRACT FROM AUTHOR]

Purple soils are greatly representative of ecologically fragile soils in southern China, yet the impact of vegetation restoration processes on the nitrogen (N) availability in purple soil ecosystems is still unclear. In this study, the soil nutrient content, available N fractions (including microbial biomass N (MBN), ammonium N (NH4+-N), nitrate N (NO3−-N), and total dissolved N (TDN)), and enzyme activities (including urease (URE), nitrate reductase (NR), and nitrite reductase (NIR)) involved in N mineralization and immobilization were investigated across the three vegetation-restoration measures: Camellia oleifera monoculture, Camellia oleifera ryegrass intercropping, and Camellia oleifera intercropping with weeds. The results showed that the Camellia oleifera monoculture mode considerably enhanced the accumulation and availability of soil N and modified the proportion of available N fractions in arable land situated on purple soil slopes, compared to the intercropping mode, the physical, chemical, and microbiological properties of soil demonstrated more pronounced effects due to the Camellia oleifera monoculture vegetation-restoration measures. However, soil nutrient loss is faster on set-aside land and in crop monocultures, and intercropping restoration measures are more beneficial for soil and water conservation under timely fertilization conditions. The soil URE, NR, and NIR activities and MBN content in the Camellia oleifera monoculture model were significantly higher than in the control check sample. Soil N transformation occurs through the combined influence of chemical and biological processes. The relationships between the activities of the three soil enzymes studied and the contents of various components of soil nutrients and effective N displayed significant differences. Notably, URE had a highly significant positive correlation with TOC. There is a strong positive correlation between NR and TN, NIR and TDN, NO3−-N, and NH4+-N. Our findings suggest that vegetation restoration improved the soil N availability and its enzyme activities in purple soils, making an essential contribution to the restoration and sustainability of purple soil ecosystem functions. [ABSTRACT FROM AUTHOR]

Nitrate ammonification is important for soil nitrogen retention. However, the ecology of ammonifiers and their prevalence compared with denitrifiers, being competitors for nitrate, are overlooked. Here, we screen 1 million genomes for nrfA and onr, encoding ammonifier nitrite reductases. About 40% of ammonifier assemblies carry at least one denitrification gene and show higher potential for nitrous oxide production than consumption. We then use a phylogeny-based approach to recruit gene fragments of nrfA, onr and denitrification nitrite reductase genes (nirK, nirS) in 1861 global terrestrial metagenomes. nrfA outnumbers the nearly negligible onr counts in all biomes, but denitrification genes dominate, except in tundra. Random forest modelling teases apart the influence of the soil C/N on nrfA-ammonifier vs denitrifier abundance, showing an effect of nitrate rather than carbon content. This study demonstrates the multiple roles nitrate ammonifiers play in nitrogen cycling and identifies factors ultimately controlling the fate of soil nitrate. Nitrate ammonifiers are poorly known despite their importance for soil nitrogen retention. This study shows that they are phylogenetically diverse and globally distributed across terrestrial biomes and that the outcome of the competition with denitrifiers is controlled by soil nitrate. [ABSTRACT FROM AUTHOR]

Nitrosomonas europaea , an aerobic ammonia oxidizing bacterium, is responsible for the first and rate-limiting step of the nitrification process, and their ammonia oxidation activities are critical for the biogeochemical cycling and the biological nitrogen removal of wastewater treatment. In the present study, N. europaea cells were cultivated in the inorganic or organic media (the NBRC829 and the nutrient-rich, NR, media, respectively), and the cells proliferated in the form of planktonic and biofilm in those media, respectively. The N. europaea cells in the biofilm growth mode produced larger amounts of the extracellular polymeric substances (EPS), and the composition of the EPS was characterized by the chemical analyses including Fourier transform infrared spectroscopy (FT-IR) and 1H-nuclear magnetic resonance (NMR) measurements. The RNA-Seq analysis of N. europaea in the biofilm or planktonic growth mode revealed that the following gene transcripts involved in central nitrogen metabolisms were abundant in the biofilm growth mode; amo encoding ammonia monooxygenase, hao encoding hydroxylamine dehydrogenase, the gene encoding nitrosocyanine, nirK encoding copper-containing nitrite reductase. Additionally, the transcripts of the pepA and wza involved in the bacterial floc formation and the translocation of EPS, respectively, were also abundant in the biofilm-growth mode. Our study was first to characterize the EPS production and transcriptome of N. europaea in the biofilm and planktonic growth mode. [ABSTRACT FROM AUTHOR]

Abstract—NO is a gaseous signaling redox-active molecule that functions in various eukaryotes. However, its synthesis, turnover, and effects in cells are specific in plants in several aspects. Compared with higher plants, the role of NO in Chlorophyta has not been investigated enough. However, some of the mechanisms for controlling the levels of this signaling molecule have been characterized in model green algae. In Chlamydomonas reinhardtii, NO synthesis is carried out by a dual system of nitrate reductase and NO-forming nitrite reductase. Other mechanisms that might produce NO from nitrite are associated with components of the mitochondrial electron-transport chain. In addition, NO formation in some green algae proceeds by an oxidative mechanism similar to that in mammals. The recent discovery of L-arginine-dependent NO synthesis in the colorless alga Polytomella parva suggests the existence of a protein complex with enzyme activities that are similar to animal nitric oxide synthase. This latter finding paves the way for further research into potential members of the NO synthases family in Chlorophyta. Beyond synthesis, the regulatory processes to maintain intracellular NO levels are also an integral part for its function in cells. Members of the truncated hemoglobins family with dioxygenase activity can convert NO to nitrate, as was shown for C. reinhardtii. In addition, the implication of NO reductases in NO scavenging has also been described. Even more intriguing, unlike in animals, the typical NO/cGMP signaling module appears not to be used by green algae. S-nitrosylated glutathione, which is considered the main reservoir for NO, provides NO signals to proteins. In Chlorophyta, protein S-nitrosation is one of the key mechanisms of action of the redox molecule. In this review, we discuss the current state-of-the-art and possible future directions related to the biology of NO in green algae. [ABSTRACT FROM AUTHOR]

Legumes can contribute to emissions of the potent greenhouse gas nitrous oxide (N2O) directly by some rhizobia species that are able to denitrify under free-living conditions and in symbiotic association with the plant. In this study, the capacity of Phaseolus vulgaris-Rhizobium etli symbiosis to emit N2O in response to nitrate (NO3-) has been demonstrated for the first time. We found that bacteroidal assimilatory nitrate reductase (NarB) as well as nitrite reductase (NirK) and nitric oxide reductase (cNor) denitrifying enzymes contribute to nitric oxide (NO) and N2O formation in nodules. We also show that R. etli NarK is involved in NO2- extrusion and links NO3- reduction by NarB in the cytoplasm with NirK and cNor denitrification activities in the periplasm. The knowledge generated in this work will be instrumental for exploring strategies and sustainable practices in agricultural soil management to increase legume crop yield and mitigate greenhouse gas emissions. HIGHLIGHTS Common bean nodules are able to produce N2O in response to nitrate. Nitrate reduction to nitrite in R. etli bacteroids catalyzed by assimilatory nitrate reductase NarB is involved in N2O emissions from common bean nodules. R. etli respiratory nitrite reductase NirK and nitric oxide reductase cNor support N2O production in common bean nodules. R. etli NarB and cNor are involved in NO homeostasis in common bean nodules. R. etli nitrite exporter NarK links nitrate reduction in the cytoplasm with denitrification activities in the periplasm. [ABSTRACT FROM AUTHOR]

Nickel (Ni) contamination hinders plant growth and yield. Nitric oxide (NO) and thiourea (Thi) aid plant recovery from heavy metal damage, but their combined effects on pepper (Capsicum annuum) plant tolerance to Ni stress need more study. Sodium nitroprusside (0.1 mM, SNP) and 400 mg L−1 Thi, alone and combined, were studied for their impact on pepper growth under Ni toxicity. Ni stress reduces chlorophyll, PSII efficiency and leaf water and sugar content. However, SNP and Thi alleviate these effects by increasing leaf water, proline and sugar content. It also increased the activities of superoxide dismutase, catalase, ascorbate peroxidase and peroxidase. Nickel stress lowered nitrogen assimilation enzymes (nitrate reductase, nitrite reductase, glutamine synthetase, glutamate synthase and glutamate dehydrogenase) and protein content, but increased nitrate, ammonium and amino acid content. SNP and Thi enhanced nitrogen assimilation, increased protein content and improved pepper plant growth and physiological functions during Ni stress. The combined treatment reduced Ni accumulation, increased Ni in leaf cell walls and potentially in root vacuoles, and decreased Ni concentration in cell organelles. It effectively mitigated Ni toxicity to vital organelles, surpassing the effects of SNP or Thi use alone. This study provides valuable insights for addressing heavy metal contamination in agricultural soils and offers potential strategies for sustainable and eco-friendly farming practices. Nickel contamination hinders plant growth and yield. Nitric oxide (NO) and thiourea aid plant recovery from heavy metal damage, but their combined effects on pepper (Capsicum annuum) tolerance to Ni stress need more study. Combined use of NO and thiourea alleviates Ni stress effects on pepper by enhancing leaf water, proline, sugar content, antioxidant enzyme activities and Ni distribution. These findings contribute valuable insights for addressing heavy metal contamination in agricultural soils and promoting sustainable and eco-friendly farming practices. [ABSTRACT FROM AUTHOR]

Nitrite (NO2−) and nitric oxide (NO) interconversion is crucial for maintaining optimum NO flux in mammalian physiology. Herein we demonstrate that [L2CuII(nitrite)]+ moieties (in 2 a and 2 b; where, L = Me2PzPy and Me2PzQu) with distorted octahedral geometry undergo facile reduction to provide tetrahedral [L2CuI]+ (in 3 a and 3 b) and NO in the presence of biologically relevant reductants, such as 4‐methoxy‐2,6‐di‐tert‐butylphenol (4‐MeO‐2,6‐DTBP, a tyrosine model) and N‐benzyl‐1,4‐dihydronicotinamide (BNAH, a NAD(P)H model). Interestingly, the reaction of excess NO gas with [L2CuII(MeCN)2]2+ (in 1 a) provides a putative {CuNO}10 species, which is effective in mediating the nitrosation of various nucleophiles, such as thiol and amine. Generation of the transient {CuNO}10 species in wet acetonitrile leads to NO2− as assessed by Griess assay and 14N/15N‐FTIR analyses. A detailed study reveals that the bidirectional NOx‐reactivity, namely, nitrite reductase (NIR) and NO oxidase (NOO), at a common CuII site, is governed by the geometric‐preference‐driven facile CuII/CuI redox process. Of broader interest, this study not only highlights potential strategies for the design of copper‐based catalysts for nitrite reduction, but also strengthens the previous postulates regarding the involvement of red copper proteins in denitrification. [ABSTRACT FROM AUTHOR]

The possibility of using the non-nitrogen-fixing cyanobacterium (Chroococcus sp.) for the reduction of soil nitrate contamination was tested through Petri dish experiments. The application of 0.03, 0.05 and 0.08 mg/cm2Chroococcus sp. efficiently removed NO3−-N from the soil through assimilation of nitrate nutrient and promotion of soil denitrification. At the optimal application dose of 0.05 mg/cm2, 44.06%, 36.89% and 36.17% of NO3−-N were removed at initial NO3−-N concentrations of 60, 90 and 120 mg/kg, respectively. The polysaccharides released by Chroococcus sp. acted as carbon sources for bacterial denitrification and facilitated the reduction of soil salinity, which significantly (p < 0.05) stimulated the growth of denitrifying bacteria (Hyphomicrobium denitrificans and Hyphomicrobium sp.) as well as significantly (p < 0.05) elevated the activities of nitrate reductase and nitrite reductase by 1.07–1.23 and 1.15–1.22 times, respectively. The application of Chroococcus sp. promoted the dominance of Nocardioides maradonensis in soil microbial community, which resulted in elevated phosphatase activity and increased available phosphorus content. The application of Chroococcus sp. positively regulated the growth of soil bacteria belonging to the genera Chitinophaga, Prevotella and Tumebacillus, which may contribute to increased soil fertility through the production of beneficial enzymes such as invertase, urease and catalase. To date, this is the first study verifying the remediation effect of non-nitrogen-fixing cyanobacteria on nitrate-contaminated soil. [ABSTRACT FROM AUTHOR]

Copper plays a critical role in controlling greenhouse gas emissions as it is a key component of the particulate methane monooxygenase and nitrous oxide reductase. Some methanotrophs excrete methanobactin (MB) that has an extremely high copper affinity. As a result, MB may limit the ability of other microbes to gather copper, thereby decreasing their activity as well as impacting microbial community composition. Here, we show using forest soil microcosms that multiple forms of MB; MB from Methylosinus trichosporium OB3b (MB‐OB3b) and MB from Methylocystis sp. strain SB2 (MB‐SB2) increased nitrous oxide (N2O) production as well caused significant shifts in microbial community composition. Such effects, however, were mediated by the amount of copper in the soils, with low‐copper soil microcosms showing the strongest response to MB. Furthermore, MB‐SB2 had a stronger effect, likely due to its higher affinity for copper. The presence of either form of MB also inhibited nitrite reduction and generally increased the presence of genes encoding for the iron‐containing nitrite reductase (nirS) over the copper‐dependent nitrite reductase (nirK). These data indicate the methanotrophic‐mediated production of MB can significantly impact multiple steps of denitrification, as well as have broad effects on microbial community composition of forest soils. [ABSTRACT FROM AUTHOR]

Shewanella oneidensis is a good model for investigating the bactericidal effects of chemical agents. In this study, the effects of tricarbonyldichlororuthenium dimer (CORM-2) on the aerobic and anaerobic growth of S. oneidensis were studied, and its bactericidal mechanisms were elucidated. CORM-2 (5 µM) significantly inhibited aerobic and anaerobic respiration. Growth potential tests showed that mutants Δ katB , Δ oxyR, Δ ccmF, and Δ crp and mutants that deleted each cytochrome c-encoding gene exhibited sensitivity to CORM-2 similar to that of the wild-type strain MR-1. Enzymatic analyses showed that cytochrome oxidase, catalase and cysteine desulfurase were activated by CORM-2, while nitrite reductase, nitrate reductase, sulfite reductase, thiosulfate reductase, peroxidase and NADH dehydrogenase were inhibited by CORM-2, and no significant changes were found in the activities of superoxide dismutase and aconitase. Promoter activity assays showed that cco , cyd , cox , katB , sirA and psrA were repressed by CORM-2. Sulfide alleviated the bactericidal effect of CORM-2 and protected NADH dehydrogenase from CORM-2 inhibition. Thus, oxidative stress and cytochrome oxidase inactivation are not the primary reasons for the bactericidal effect of CORM-2, and NADH dehydrogenase is the main target in S. oneidensis. The bactericidal effect of CORM-2 is caused by the toxicity of Ru2+, not by carbon monoxide. [Display omitted] • The first paper to investigate the effect of CORM-2 on the growth of S. oneidensis. • Cytochrome oxidase, catalase and cysteine desulfurase are activated by CORM-2. • Oxidative stress is not the major bactericidal reason of CORM-2 in S. oneidensis. • NADH dehydrogenase is the main target of CORM-2 in S. oneidensis. • The bactericidal effect of CORM-2 is caused by Ru2+, not by CO. [ABSTRACT FROM AUTHOR]