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Biological nitrogen fixation provides fixed nitrogen for microbes living in the oligotrophic open ocean. UCYN-A2, the previously known symbiont of Braarudosphaera bigelowii, now believed to be an early-stage B. bigelowii organelle that exchanges fixed nitrogen for fixed carbon, is globally distributed. Indirect evidence suggested that B. bigelowii might be a mixotrophic (phagotrophic) phototrophic flagellate. The goal of this study was to determine if B. bigelowii can graze on bacteria using several independent approaches. The results showed that B. bigelowii grazed on co-occurring bacteria at a rate of 5-7 cells/h/B. bigelowii and that the overall grazing rate was significantly higher at nighttime than at daytime. Bacterial abundance changes, assessed with 16S rRNA gene amplicon sequencing analysis, may have indicated preferential grazing by B. bigelowii on specific bacterial genotypes. In addition, Lysotracker™ staining of B. bigelowii suggested digestive activity inside B. bigelowii. Carbon and nitrogen fixation measurements revealed that the carbon demand of B. bigelowii could not be fulfilled by photosynthesis alone, implying supplementation by heterotrophy. These independent lines of evidence together revealed that B. bigelowii engages in phagotrophy, which, beyond serving as a supplementary source of carbon and energy, may also facilitate the indirect assimilation of inorganic nutrients.

BackgroundMercury (Hg) is highly toxic and has the potential to cause severe health problems for humans and foraging animals when transported into edible plant parts. Soil rhizobia that form symbiosis with legumes may possess mechanisms to prevent heavy metal translocation from roots to shoots in plants by exporting metals from nodules or compartmentalizing metal ions inside nodules. Horizontal gene transfer has potential to confer immediate de novo adaptations to stress. We used comparative genomics of high quality de novo assemblies to identify structural differences in the genomes of nitrogen-fixing rhizobia that were isolated from a mercury (Hg) mine site that show high variation in their tolerance to Hg.ResultsOur analyses identified multiple structurally conserved merA homologs in the genomes of Sinorhizobium medicae and Rhizobium leguminosarum but only the strains that possessed a Mer operon exhibited 10-fold increased tolerance to Hg. RNAseq analysis revealed nearly all genes in the Mer operon were significantly up-regulated in response to Hg stress in free-living conditions and in nodules. In both free-living and nodule environments, we found the Hg-tolerant strains with a Mer operon exhibited the fewest number of differentially expressed genes (DEGs) in the genome, indicating a rapid and efficient detoxification of Hg from the cells that reduced general stress responses to the Hg-treatment. Expression changes in S. medicae while in bacteroids showed that both rhizobia strain and host-plant tolerance affected the number of DEGs. Aside from Mer operon genes, nif genes which are involved in nitrogenase activity in S. medicae showed significant up-regulation in the most Hg-tolerant strain while inside the most Hg-accumulating host-plant. Transfer of a plasmid containing the Mer operon from the most tolerant strain to low-tolerant strains resulted in an immediate increase in Hg tolerance, indicating that the Mer operon is able to confer hyper tolerance to Hg.ConclusionsMer operons have not been previously reported in nitrogen-fixing rhizobia. This study demonstrates a pivotal role of the Mer operon in effective mercury detoxification and hypertolerance in nitrogen-fixing rhizobia. This finding has major implications not only for soil bioremediation, but also host plants growing in mercury contaminated soils.

We describe the genome of an Eremiobacterota population from tundra soil that contains the minimal set of nif genes needed to fix atmospheric N2. This putative diazotroph population, which we name Candidatus Lamibacter sapmiensis, links for the first time Eremiobacterota and N2 fixation. The integrity of the genome and its nif genes are well supported by both environmental and taxonomic signals. Ca. Lamibacter sapmiensis contains three nifH homologues and the complementary set of nifDKENB genes that are needed to assemble a functional nitrogenase. The putative diazotrophic role of Ca. Lamibacter sapmiensis is supported by the presence of genes that regulate N2 fixation and other genes involved in downstream processes such as ammonia assimilation. Similar to other Eremiobacterota, Ca. Lamibacter sapmiensis encodes the potential for atmospheric chemosynthesis via CO2 fixation coupled with H2 and CO oxidation. Interestingly, the presence of a N2O reductase indicates that this population could play a role as a N2O sink in tundra soils. Due to the lack of activity data, it remains uncertain if Ca. Lamibacter sapmiensis is able to assemble a functional nitrogenase and participate in N2 fixation. Confirmation of this ability would be a testament to the great metabolic versatility of Eremiobacterota, which appears to underlie their ecological success in cold and oligotrophic environments.

Biological nitrogen fixation by free-living bacteria and rhizobial symbiosis with legumes plays a key role in sustainable crop production. Here, we study how different crop combinations influence the interaction between peanut plants and their rhizosphere microbiota via metabolite deposition and functional responses of free-living and symbiotic nitrogen-fixing bacteria. Based on a long-term (8 year) diversified cropping field experiment, we find that peanut co-cultured with maize and oilseed rape lead to specific changes in peanut rhizosphere metabolite profiles and bacterial functions and nodulation. Flavonoids and coumarins accumulate due to the activation of phenylpropanoid biosynthesis pathways in peanuts. These changes enhance the growth and nitrogen fixation activity of free-living bacterial isolates, and root nodulation by symbiotic Bradyrhizobium isolates. Peanut plant root metabolites interact with Bradyrhizobium isolates contributing to initiate nodulation. Our findings demonstrate that tailored intercropping could be used to improve soil nitrogen availability through changes in the rhizosphere microbiome and its functions.

Marine macroalgae produce abundant and diverse polysaccharides, which contribute substantially to the organic matter exported to the deep ocean. Microbial degradation of these polysaccharides plays an important role in the turnover of macroalgal biomass. Various members of the Planctomycetes-Verrucomicrobia-Chlamydia (PVC) superphylum are degraders of polysaccharides in widespread anoxic environments. In this study, we isolated a novel anaerobic bacterial strain NLcol2T from microbial mats on the surface of marine sediments offshore Santa Barbara, CA, USA. Based on 16S ribosomal RNA (rRNA) gene and phylogenomic analyses, strain NLcol2T represents a novel species within the Pontiella genus in the Kiritimatiellota phylum (within the PVC superphylum). Strain NLcol2T is able to utilize various monosaccharides, disaccharides, and macroalgal polysaccharides such as agar and ɩ-carrageenan. A near-complete genome also revealed an extensive metabolic capacity for anaerobic degradation of sulfated polysaccharides, as evidenced by 202 carbohydrate-active enzymes (CAZymes) and 165 sulfatases. Additionally, its ability of nitrogen fixation was confirmed by nitrogenase activity detected during growth on nitrogen-free medium, and the presence of nitrogenases (nifDKH) encoded in the genome. Based on the physiological and genomic analyses, this strain represents a new species of bacteria that may play an important role in the degradation of macroalgal polysaccharides and with relevance to the biogeochemical cycling of carbon, sulfur, and nitrogen in marine environments. Strain NLcol2T (= DSM 113125T = MCCC 1K08672T) is proposed to be the type strain of a novel species in the Pontiella genus, and the name Pontiella agarivorans sp. nov. is proposed.IMPORTANCEGrowth and intentional burial of marine macroalgae is being considered as a carbon dioxide reduction strategy but elicits concerns as to the fate and impacts of this macroalgal carbon in the ocean. Diverse heterotrophic microbial communities in the ocean specialize in these complex polymers such as carrageenan and fucoidan, for example, members of the Kiritimatiellota phylum. However, only four type strains within the phylum have been cultivated and characterized to date, and there is limited knowledge about the metabolic capabilities and functional roles of related organisms in the environment. The new isolate strain NLcol2T expands the known substrate range of this phylum and further reveals the ability to fix nitrogen during anaerobic growth on macroalgal polysaccharides, thereby informing the issue of macroalgal carbon disposal.

UNLABELLED: Diazotrophic bacteria can reduce atmospheric nitrogen into ammonia enabling bioavailability of the essential element. Many diazotrophs closely associate with plant roots increasing nitrogen availability, acting as plant growth promoters. These associations have the potential to reduce the need for costly synthetic fertilizers if they could be engineered for agricultural applications. However, despite the importance of diazotrophic bacteria, genetic tools are poorly developed in a limited number of species, in turn narrowing the crops and root microbiomes that can be targeted. Here, we report optimized protocols and plasmids to manipulate phylogenetically diverse diazotrophs with the goal of enabling synthetic biology and genetic engineering. Three broad-host-range plasmids can be used across multiple diazotrophs, with the identification of one specific plasmid (containing origin of replication RK2 and a kanamycin resistance marker) showing the highest degree of compatibility across bacteria tested. We then demonstrated modular expression by testing seven promoters and eleven ribosomal binding sites using proxy fluorescent proteins. Finally, we tested four small molecule inducible systems to report expression in three diazotrophs and demonstrated genome editing in Klebsiella michiganensis M5al. ONE-SENTENCE SUMMARY: In this study, broad-host plasmids and synthetic genetic parts were leveraged to enable expression tools in a library of diazotrophic bacteria.

Recent findings of NO near Gale Crater on Mars have been explained by two pathways: formation of nitric acid (HNO3) in a warm climate or formation of peroxynitric acid (HO2NO2) in a cool climate. Here, we put forth two hitherto unexplored pathways: (a) deposition of nitric/peroxynitric acid onto ice particles in a cold atmosphere, which settle quickly onto Mars' surface and (b) solar energetic particle‐induced production of nitric/peroxynitric acid. The deposition rates are enhanced and NO production is more efficient under the higher atmospheric pressures typical of Mars' ancient atmosphere. Depending on the unknown rate at which nitric/peroxynitric acid is lost from the surface, the new pathways could result in larger NO‐levels than those detected by the Mars Science Laboratory. We predict a 2:1 ratio of nitrite:nitrate would have deposited in cool surface climates with an icy atmosphere, whereas orders of magnitude more nitrate than nitrite is expected from warm surface climates. Plain Language Summary: The nitrogen oxides discovered in present‐day soil on Mars likely formed in the atmosphere before being deposited on the ground. Two possible mechanisms are deposition of nitric acid (HNO3) when Mars had a warm climate and deposition of peroxynitric acid (HO2NO2) during cold climate. The latter scenario involves processes that have not been considered previously and leads to a much faster deposition rate for nitrogen oxides than was reported in previous studies: solar energetic particles splitting N2 in the middle atmosphere, reactions of nitrogen oxides on the surfaces of ice particles in the atmosphere, and deposition of peroxynitric acid onto the Martian surface when surface pressure was higher. Depending on the unknown rate at which they are lost from the surface due to UV photolysis, the maximum accumulation rate for nitrogen oxides could be much larger than is required to explain the present day measurements. We predict that more nitrite would form than nitrate in a cool climate with an icy atmosphere, whereas in a warm climate much more nitrate than nitrite is expected. So, an investigation of the relative amounts of NO2:NO3 in the soil in the present‐day measurements could reveal the climate state under which the salts formed. Key Points: In a cold climate, heterogeneous reactions with atmospheric ice particles would cause faster deposition of HNOx than dry depositionFormation of HNOx species is faster for earlier Martian climates of larger surface pressureModeled NO accumulates to amounts greater than present‐day measurements, so we propose there may be a loss mechanism that is unidentified [ABSTRACT FROM AUTHOR]

Despite the importance of alkaline seafloor hydrothermal vents in broadening our understanding of deep-sea hydrothermal ecosystems, little is known about the mobility and concentrations of micronutrient transition metals in these environments. Here, we present new analyses of micronutrient transition metal concentrations in vent fluids from the iconic Lost City Hydrothermal Field (LCHF) and report concentrations of Fe = 2.9–18.3 µmol/kg, Zn = 1.30–5.86 µmol/kg, Cu = 0.43–5.06 µmol/kg, Ni = 86.4–556 nmol/kg, Mn = 8.3–274 nmol/kg, V = 25.9–127 nmol/kg, Mo = 24–94 nmol/kg, Co = 8.0–135 nmol/kg, W = 4.8–16 nmol/kg, and Cd = 1.7–4.5 nmol/kg. We additionally present results of a hydrothermal lherzolite alteration experiment conducted at 300 °C, 500 bar. Transition metal concentrations and major chemical parameters of experimental reaction fluids are broadly similar to LCHF vent fluids, indicating that transition metal concentrations in LCHF vent fluids, and alkaline hydrothermal fluids more generally, reflect metal solubility controlled by underlying rock-buffered hydrothermal reactions. Concentrations of Ni and Mo are especially noteworthy because of their recognized importance for biological methanogenesis (Ni) and nitrogen fixation (Mo). When compared with known biological thresholds, our findings indicate that Ni concentrations in LCHF vent fluids are sufficient to support the robust methane-metabolizing microbial communities observed in the immediate vicinity of LCHF vents and suggest that Ni availability influences the spatial distribution of LCHF methanogens. Furthermore, our laboratory hydrothermal experiments demonstrate that Mo concentrations of similar magnitude to those observed in LCHF vent fluids (and also modern seawater) can be obtained by hydrothermal alteration of ultramafic rocks with Mo-free (Na, Ca) Cl aqueous solution. Thus, we conclude that alkaline hydrothermal fluids were likely similarly enriched in Mo prior to oxidation of the Earth's atmosphere and ocean, providing localized Mo-rich geochemical environments capable of supporting Mo-dependent nitrogen fixation at currently recognized threshold concentrations. [ABSTRACT FROM AUTHOR]

Increasing biological nitrogen (N) fixation (BNF) in maize production could reduce the environmental impacts of N fertilizer use, but reactive N in the rhizosphere of maize limits the BNF process. Using non-transgenic methods, we developed gene-edited strains of Klebsiella variicola (Kv137-2253) and Kosakonia sacchari (Ks6-5687) bacteria optimized for root-associated BNF and ammonium excretion in N-rich conditions. The aim of this research was to elucidate the mechanism of action of these strains. We present evidence from in vitro, in planta and field experiments that confirms that our genetic remodeling strategy derepresses BNF activity in N-rich systems and increases ammonium excretion by orders of magnitude above the respective wildtype strains. BNF is demonstrated in controlled environments by the transfer of labeled 15N2 gas from the rhizosphere to the chlorophyll of inoculated maize plants. This was corroborated in several 15N isotope tracer field experiments where inoculation with the formulated, commercial-grade product derived from the gene-edited strains (PIVOT BIO PROVEN® 40) provided on average 21 kg N ha-1 to the plant by the VT-R1 growth stages. Data from small-plot and on-farm trials suggest that this technology can improve crop N status pre-flowering and has potential to mitigate the risk of yield loss associated with a reduction in synthetic N fertilizer inputs. [ABSTRACT FROM AUTHOR]

Silicon (Si) supplementation can enhance symbiotic functions in some legumes (Fabaceae) with their nitrogen‐fixing rhizobia, such as root nodulation and nitrogen fixation. However, it is still poorly understood how Si influences legume–insect interactions. Here, we investigated how a symbiotic legume responds not only to Si supplementation but also to herbivory treatment with varying infestation levels in two events. We conducted a controlled climate chamber experiment by growing Medicago truncatula plants inoculated with rhizobia. For half of the plants, the soil was kept without Si (−Si), whereas the other half was regularly supplemented with Si (+Si). We then infested the plants with caterpillars of Spodoptera littoralis with 0, 1 or 3 larvae and 0, 1 or 1 larva in single herbivory attack and in double herbivory attack, respectively. To understand plant responses to such treatment combinations, we examined 16 functional traits. Nodule number, nodule fresh mass and nodule leghaemoglobin concentrations were not affected in single attack plants. However, increasing levels of herbivory led to decreases in such measured traits in double attack plants. Foliar C to N ratio increased in single attack plants but decreased in double attack plants with increasing levels of herbivory, indicating contrasting resource allocation. Herbivory did not affect the content of foliar Si, which was higher in +Si than −Si plants. Si and herbivory led to reduced foliar phenolics in double attack plants, suggesting a potential trade‐off between silicification and phenolic production. Si and herbivory led to increased trichome densities in single attack plants, but patterns were less clear in double attack plants. Herbivory but not Si reduced plant biomass with increasing levels of herbivory in double attack plants. Relative growth rates of the caterpillars, as proxy for plant resistance, decreased mainly due to herbivory treatment, when fed on single attack plants. Using a trait‐based approach, we provide novel insights to better understand the response of a legume to Si supplementation and different herbivory levels and events. We conclude that herbivory predominantly exerts much stronger effects than Si on various plant traits, pointing to a necessity to respond to herbivory by induced defence strategies. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Sustainable intensification of livestock systems implies greater efficiency in resource utilization resulting in greater output of products and other ecosystem services per unit of resource input. Integrating forage legumes into livestock systems is a viable way to reduce the input of industrial N fertilizer, reducing the use of fossil fuels and helping to mitigate global warming, a major problem during the Anthropocene. Some forage legumes have greater concentrations of secondary compounds, such as condensed tannins, that might reduce the emission of greenhouse gases (GHG) from ruminant eructation and excreta. Furthermore, forage legumes might enhance cattle performance because of greater nutritive value, resulting in greater production per unit of GHG released. Shortening the production cycle and improving cattle reproductive efficiency could have a major impact on reducing the overall carbon footprint of the system. Grazing systems with more diversified plant species are typically more resistant and resilient, adapting to current climate changes during the Anthropocene. Novel technologies might accelerate the development of future grazing systems using forage legumes as a key component. Breeding efforts for the next‐generation legumes must focus on adaptation and potential use for mitigation of negative environmental impacts. There are examples of successful integration of forage legumes into livestock systems in different regions of the world, with a major reduction in off‐farm inputs and maintaining the system productive. These successful examples could be used to increase adoption and improve the efficiency of current livestock systems. [ABSTRACT FROM AUTHOR]

ABSTRACT Extensive foliar shedding in monoculture soybeans post‐anthesis negatively impacts yield, whereas relay strip intercropping prolongs leaf area duration, enhancing productivity. However, little is known about the causes of leaf shedding in monoculture and its impact on physiological functions and plasticity of source and sink organs, we conducted a 4‐year field experiment and leaf‐removal simulations in relay intercropped soybeans. Results revealed that monoculture soybeans experienced severe self‐shading and defoliation, while relay intercropping maintained better light conditions, supporting higher leaf area, nodule numbers, and carbon allocation. Increasing leaf removal initially increased leaf area but eventually reduced it. Extensive leaf‐removal reduced Rubisco and sucrose phosphate synthase (SPS) activity, as well as sucrose, malate, ATP, and energy charge (EC) in nodules, revealing a trade‐off between leaf growth and nodule development. Moderate leaf‐removal (L30), however, balanced compensation and consumption, increasing total non‐structural carbohydrates (TNC) in roots and N and ureide in leaves and pods. Network analysis showed that L30 improved the synergies of functional traits in leaves and nodules, ultimately benefiting overall plant growth and nutrient accumulation in pods. This study elucidates a mechanism of foliar shedding and highlights how relay strip intercropping optimizes source‐sink coordination to enhance photosynthesis and nitrogen fixation. [ABSTRACT FROM AUTHOR]

Iron‐based catalysts play an important role in the ammonia industry. As one of the most abundant iron minerals, Fe3O4 containing FeII and FeIII sites is widely distributed in the earth's crust and even on exoplanets, theoretically giving it both economic and catalytic potentials in ammonia synthesis. However, in the absence of specific active co‐catalyst and harsh conditions, Fe3O4 is impossible to achieve ammonia synthesis alone. Here, we designed to activate the relatively inert FeII and FeIII sites in Fe3O4 with a third FeIII site inlayed in a coordination framework (MIL‐101(Fe)) to achieve the unpresented multi‐site collaborative catalysis. In‐depth mechanism study confirmed the roles of three different Fe sites in N2 activation, H2 activation, and product transfer, respectively. Efficient N2−H2 activation to NH3 on the Fe3O4‐based catalytic system has been achieved at extremely mild conditions. Our research provides a theoretical basis and a new strategy for designing efficient non‐noble metal‐based ammonia synthesis catalyst with minimized energy consumption. [ABSTRACT FROM AUTHOR]

The catalytic system of biological nitrogen fixation in nature primarily relies on the "FeMo cofactor" within nitrogenase enzymes. Inspired by this natural structure, we have designed a bionic inorganic counterpart, iron‐doped MoSe2, for the efficient electroreduction of dinitrogen to ammonia. The introduced Fe dopant significantly enhances nitrogen fixation activity of MoSe2. Furthermore, we constructed a heterostructure catalyst, the Fe‐MoSe2/Mo2C with more versatile Mo valence states. The heterostructured electrocatalyst achieves an ammonia production rate of 3.38 μg cm−2 h−1, and a Faradaic efficiency of 30.8 %, which is ~5 fold higher than that of pristine MoSe2. This study presents a novel approach for designing bionic nitrogen fixation electrocatalysts. [ABSTRACT FROM AUTHOR]

Introduction: Understanding the microbial diversity and potential functional dynamics within the rhizocompartments of Dendrobium huoshanense is crucial for unraveling the plant–microbe interactions that influence its medicinal properties. Methods: This study is the first to characterize the microbiome associated with the rhizocompartments of D. huoshanense , including its cultivation medium, rhizosphere, rhizoplane, and root endosphere, using high-throughput sequencing and subsequent bioinformatic analysis. Results: Bacterial phylogenetic diversity was significantly higher in the endosphere than in the rhizosphere, while fungal α-diversity significantly decreased from the cultivation medium to the endosphere. Both bacterial and fungal niche widths decreased from the cultivation medium to the endosphere. β-Diversity analysis revealed distinct spatial patterns in both bacterial and fungal communities across the rhizocompartments, with the most pronounced differences between the cultivation medium and the endosphere. Taxonomically, Proteobacteria and Ascomycota were predominant in the endosphere for bacterial and fungal communities, respectively. Functional predictions showed significant enrichment of pathways related to xenobiotics biodegradation, lipid metabolism, and nitrogen fixation in the endosphere, while functions associated with plant pathogens and saprotrophs were significantly reduced. Discussion: The results indicate a shift from generalist to specialist microbes from the cultivation medium to the endosphere, suggesting that D. huoshanense exerts strong selective pressure for endophytic fungi. Interestingly, a high proportion of fungi with unknown functions were found in the endosphere, highlighting an area for further research regarding the medicinal efficacy of D. huoshanense. Overall, this study provides foundational data for understanding the adaptive evolution of these microbial communities in response to specific microhabitats. [ABSTRACT FROM AUTHOR]

Diazotrophic cyanobacteria can fix nitrogen gas (N2) but are usually scarce in nitrogen-limited coastal waters, which poses an apparent ecological paradox. One hypothesis is that high salinities (> 10 g/L NaCl) may inhibit cyanobacterial N2 fixation. However, here we show that N2 fixation in a unicellular coastal cyanobacterium exclusively depends on sodium ions and is inhibited at low NaCl concentrations (< 4 g/L). In the absence of Na+, cells of Cyanothece sp. ATCC 51142 (recently reclassified as Crocosphaera subtropica) upregulate the expression of nifHDK genes and synthesise a higher amount of nitrogenase, but do not fix N2 and do not grow. We find that the loss of N2-fixing ability in the absence of Na+ is due to insufficient ATP supply. Additional experiments suggest that N2 fixation in this organism is driven by sodium energetics and mixed-acid fermentation, rather than proton energetics and aerobic respiration, even though cells were cultured aerobically. Further work is needed to clarify the underlying mechanisms and whether our findings are relevant to other coastal cyanobacteria. High salinities are thought to inhibit nitrogen fixation by cyanobacteria in coastal waters. In contrast, Tang et al. show that nitrogen fixation in a coastal cyanobacterium requires sodium ions and is apparently driven by sodium energetics and mixed-acid fermentation. [ABSTRACT FROM AUTHOR]

The Ostwald process, which is producing HNO3 for commercial use, involves the catalytic oxidation of NH3 and a series of chemical reactions conducted under severe operating conditions. Due to their energy‐intensive nature, these activities play a major role in greenhouse gas emissions and global energy consumption. In response to the urgent requirements of the global energy and environmental sectors, there is an increasingly critical need to develop novel, highly efficient, and environmentally sustainable methods. Herein, CoPc/C3N4 electrocatalyst, integrating CoPc nanotubes with C3N4 nanosheets, is shown. The CoPc/C3N4 electrocatalyst demonstrates yield rate of 871.8 µmol h−1 gcat−1 at 2.2 V, with corresponding Faradaic efficiency (FE) of 46.4% at 2.1 V, which notably surpasses that of CoPc. Through a combination of experimental investigations and density functional theory (DFT) calculations, this study shows that CoPc anchored on C3N4 effectively simplifies the adsorption and activation of chemically inactive nitrogen molecules. The improved catalytic activity for composite system may be the reason of re‐distribution of charges over the CoPc, tuning the valence orbital of Co center due to the presence of 2D layer of C3N4. This mechanism significantly lowers the energy barrier required for critical breaking of inert N2, ultimately leading to a significant improvement in N2 oxidation efficiency. [ABSTRACT FROM AUTHOR]

Oxygenic photosynthesis is characterised by the cooperation of two photo-driven complexes, Photosystem II (PSII) and Photosystem I (PSI), sequentially linked through a series of redox-coupled intermediates. Divergent evolution has resulted in photosystems exhibiting complementary redox potentials, spanning the range necessary to oxidise water and reduce CO2 within a single system. Catalysing nature's most oxidising reaction to extract electrons from water is a highly specialised task that limits PSII's metabolic function. In contrast, potential electron donors in PSI span a range of redox potentials, enabling it to accept electrons from various metabolic processes. This metabolic flexibility of PSI underpins the capacity of photosynthetic organisms to balance energy supply with metabolic demands, which is key for adaptation to environmental changes. Here, we review the phenomenon of 'PSII-less photosynthesis' where PSI functions independently of PSII by operating cyclic electron flow using electrons derived from non-photochemical reactions. PSII-less photosynthesis enables supercharged ATP production and is employed, for example, by cyanobacteria's heterocysts to host nitrogen fixation and by bundle sheath cells of C4 plants to boost CO2 assimilation. We discuss the energetic benefits of this arrangement and the prospects of utilising it to improve the productivity and stress resilience of photosynthetic organisms. Oxygenic photosynthesis typically relies on two photo-driven complexes, Photosystem II (PSII) and Photosystem I (PSI). However, PSI can operate independently to boost energy production and amplify nitrogen fixation and CO2 capture in specialised cells. In this review, we propose that 'PSII-less photosynthesis' allows photosynthetic organisms to better balance energy needs and adapt to changing environments. We explore the potential of harnessing this process to improve crop productivity and stress resilience. [ABSTRACT FROM AUTHOR]

Trichoderma species are ubiquitous saprophytic fungi commonly found in soil, with potential as fungal biocontrol agents for plant disease control and growth promotion. This research aimed to assess the attributes of Trichoderma sp. as plant growth promoters, focusing on nitrogen fixation, siderophore production, plant nutrient solubilization and indole-3-acetic acid production. Out of 19 isolates tested, 6 (T05, T19, T25, T27, T28 and T33) showed superior plant growth promotion abilities. These isolates were further evaluated for their capacity to enhance the germination of Khao Dawk Mali 105 rice seeds. Seeds were soaked in a suspension of conidia at a concentration of 1x1012 conidia/mL, and germination rates were measured. The germination rate ranged between 77.67 - 86.67%, statistically significantly higher than the control rate of 33.33%. Among the isolates, T05 exhibited the highest promotion of plant growth, evidenced by root length (7.27 cm), shoot length (8.50 cm), fresh weight (0.54 g) and dry weight (0.27 g), all significantly different from the control. Additionally, the potential of isolates to inhibit the fungal pathogen Colletotrichum sp. MN-3 was assessed using a dual culture method, with T35 showing the highest inhibition percentage (60.90%). Morphological classification and nucleotide sequencing of the ITS1-5.8S-ITS2 region of rDNA gene identified the isolates as T. harzianum, T. reesei, T. asperellum and T. longibrachiatum. These findings underscore the effectiveness of Trichoderma sp. in promoting plant growth and suppressing plant pathogenic fungi. [ABSTRACT FROM AUTHOR]

Cyanobacteria, renowned for their nitrogen‐fixing characteristics, are important for sustainable biomanufacturing and agricultural innovation. This review explores the synergy between cyanobacteria and nitrogen fixation, highlighting their potential to revolutionize biobased compound production and reduce the ecological impact of traditional nitrogen sources. It focuses on genetic enhancements and synthetic biology techniques, which transform these microorganisms into sustainable nitrogen providers. Current applications range from agricultural enhancement to cutting‐edge biotechnology, highlighting the important consequences of cyanobacterial nitrogen fixation. Challenges persist, however, requiring a meticulous analysis of ecological, regulatory, and scalability concerns. The untapped potential of cyanobacteria in nitrogen fixation promises a significant shift in biomanufacturing and environmental stewardship. The aim of this article is to inspire high‐impact research and transformative applications in biotechnology and sustainability. [ABSTRACT FROM AUTHOR]

Nicosulfuron residues in soil can be harmful to the environment. In this study, Klebsiella oxytoca ES5 and Klebsiella grimontii ES8 were isolated to construct the ES58 bacterial complex. The culture medium was optimized using response surface methodology, nicosulfuron degradation by ES58 reached 97.21 % in 96 h. The optimal degradation conditions were: temperature: 25℃, pH 6, initial nicosulfuron concentration: 50 mg L−1 and inoculum volume: 2 %. The two individual strains and the bacterial complex were tested for the ability of nitrogen fixation, phosphorus solubilization, potassium decomposition and iron carrier production. The results revealed that both strains and the bacterial complex had the ability to promote the growth, with bacterial complex being more capable than the two individual bacterial strains. After 28 d of bioremediation of nicosulfuron-contaminated soil by ES58, degradation rate of nicosulfuron was 90.84 % in the unsterilized soil. Furthermore, the remediation process restored the activities of catalase, invertase, dehydrogenase and urease in the soil. The ES5-specific gene budA and ES8-specific gene ldh were detected in the soil at the 28th day. ES58 exhibited different effects on the growth indexes of nicosulfuron-sensitive crops. The study provides a novel strategy for nicosulfuron degradation effective by constructing and utilizing bacterial complex. [Display omitted] • Two strains of nicosulfuron efficient degrading bacteria were isolated and identified. • The degradation characteristics of the complex bacterium ES58 were investigated. • The growth-promoting ability of the composite bacterium ES58 was determined. • Bioremediation of nicosulfuron contaminated soil by the complex bacterium ES58 was studied. [ABSTRACT FROM AUTHOR]

Three strains of Gram‐negative bacterium, Rhizobium, were developed by gamma (γ)‐irradiation random mutagenesis. The developed strains were evaluated for their augmented features for symbiotic association, nitrogen fixation, and crop yield of three leguminous plants—chickpea, field‐pea, and lentil—in agricultural fields of the northern Indian state of Haryana. Crops treated with developed mutants exhibited significant improvement in plant features and the yield of crops when compared to the control‐uninoculated crops and crops grown with indigenous or commercial crop‐specific strains of Rhizobium. This improvement was attributed to generated mutants, MbPrRz1 (on chickpea), MbPrRz2 (on lentil), and MbPrRz3 (on field‐pea). Additionally, the cocultured symbiotic response of MbPrRz1 and MbPrRz2 mutants was found to be more pronounced on all three crops. The statistical analysis using Pearson's correlation coefficients revealed that nodulation and plant biomass were the most related parameters of crop yield. Among the effectiveness of developed mutants, MbPrRz1 yielded the best results for all three tested crops. Moreover, the developed mutants enhanced macro‐ and micronutrients of the experimental fields when compared with fields harboring the indigenous rhizobial community. These developed mutants were further genetically characterized, predominantly expressing nitrogen fixation marker, nifH, and appeared to belong to Mesorhizobium ciceri (MbPrRz1) and Rhizobium leguminosarum (both MbPrRz2 and MbPrRz3). In summary, this study highlights the potential of developed Rhizobium mutants as effective biofertilizers for sustainable agriculture, showcasing their ability to enhance symbiotic relationships, crop yield, and soil fertility. [ABSTRACT FROM AUTHOR]

Nitrogen (N) availability limits plant growth and soil carbon (C) sequestration in N‐limited ecosystems, however, plant and soil C feedback on the free‐living nitrogen fixation (FLNF) process is poorly understood. Moreover, whether this feedback is influenced by initial N availability in leguminous and non‐leguminous forest soils has not been clarified. Here, we found that the addition of plant‐ and microbial‐derived C significantly enhanced soil nitrogenase activity (13∼28%) and that microbial‐derived C had a more positive impact. These positive effects were attributed to the direct C‐energy supply (0.49∼0.84) rather than variations in soil microbial activity (−0.01∼0.21) and substrate resources (−0.45∼0.27). Long‐term N addition did not inhibit FLNF. C addition promoted FLNF in soils of the two forests, but the response rate was higher in the leguminous forest soils. Our study reveals that increased soil C availability can drive FLNF in tropical forests, enhancing our understanding of the soil C‐N coupling mechanism. Plain Language Summary: Explicit consideration of controlling factors for free‐living nitrogen fixation (an important process of nitrogen biogeochemistry), is critical to understanding the response of ecosystems to environmental change. Our study reveals a previously overlooked but important process in which increased soil carbon availability exerts positive feedback on soil nitrogen inputs via free‐living nitrogen fixation. This insight enhances our understanding of soil carbon‐nitrogen coupling mechanisms and highlights an important nitrogen source in tropical forests based on increased vegetation and soil carbon sink conditions under global environmental change scenario. Key Points: Carbon (C) input affected free‐living nitrogen fixation (FLNF) more than nitrogen (N) application in tropical forest soilsBoth plant‐ and microbial‐derived C enhanced FLNF, but microbial‐derived C had a more positive impactC addition promoted FLNF in soils of the two forests, but the response rate was higher in the leguminous forest soils [ABSTRACT FROM AUTHOR]

Introduction: The chickpea (Cicer arietinum L.) is well-known for having climate resilience and atmospheric nitrogen fixation ability. Global demand for nitrogenous fertilizer is predicted to increase by 1.4% annually, and the loss of billions of dollars in farm profit has drawn attention to the need for alternative sources of nitrogen. The ability of chickpea to obtain sufficient nitrogen via its symbiotic relationship with Mesorhizobium ciceri is of critical importance in determining the growth and production of chickpea. Methods: To support findings on nodule formation in chickpea and to map the genomic regions for nodulation, an association panel consisting of 271 genotypes, selected from the global chickpea germplasm including four checks at four locations, was evaluated, and data were recorded for nodulation and 12 yield-related traits. A genome-wide association study (GWAS) was conducted using phenotypic data and genotypic data was extracted from whole-genome resequencing data of chickpea by creating a hap map file consisting of 602,344 single-nucleotide polymorphisms (SNPs) in the working set with best-fit models of association mapping. Results and Discussion: The GWAS panel was found to be structured with sufficient diversity among the genotypes. Linkage disequilibrium (LD) analysis showed an LD decay value of 37.3 MB, indicating that SNPs within this distance behave as inheritance blocks. A total of 450 and 632 stringent marker-trait associations (MTAs) were identified from the BLINK and FarmCPU models, respectively, for all the traits under study. The 75 novel MTAs identified for nodulation traits were found to be stable. SNP annotations of associated markers were found to be related to various genes including a few auxins encoding as well as nod factor transporter genes. The identified significant MTAs, candidate genes, and associated markers have the potential for use in marker-assisted selection for developing high-nodulation cultivars after validation in the breeding populations. [ABSTRACT FROM AUTHOR]

Nitrogen fixation is crucial for plant growth and global agriculture, especially with the projected population growth requiring a significant increase in food production. Traditional nitrogen fixation relies on the Haber-Bosch (H-B) process, which is energy-intensive and environmentally harmful due to greenhouse gas emissions. Emerging technologies, such as cold plasma, offer promising alternatives with lower energy consumption. Cold plasma facilitates reactive nitrogen species generation under ambient conditions, potentially improving the production efficiency of nitrogen oxides (NOx). However, optimizing cold plasma nitrogen fixation requires a synergy between experimental and theoretical approaches. Accurate input data are essential for refining theoretical models, which can then guide the design of more efficient processes. This integrated approach can leverage renewable energy, operate on smaller scales, and minimize environmental impacts, making cold plasma a sustainable solution for future nitrogen fixation needs. [ABSTRACT FROM AUTHOR]

Recurring use of chemical fertilizers (CFs) in agriculture has resulted the remarkable improvement in crop productivity but their ruinous effects on environment have made a serious issue. Biological entities (e.g., several microorganisms) showing fertilizer‐like activities have gained attention in this regard. Several soil resident microorganisms interact strongly with neighboring plants and promote the growth and development of those plants through various means. In exchange of this, microbes utilize different compounds released from plant roots for their own nutrition. This mutualistic mode of interrelation predominantly relies on the transmission of signals from microbes to plants and vice versa. However, climatic factors (e.g., CO2 level, temperature, and water availability) are also important for this association. These bacterial strains are literally known as plant growth promoting rhizobacteria (PGPR) which facilitate plant growth through nitrogen fixation, mineral solubilization, phytostimulation, stress resistance, etc. Responding to the external environmental stimuli, they often modulate the expression of genes responsible for the transport of nutrients. Reduction of the use of CFs through the application of PGPR strains in the cultivation of some economically important plants has been reported by several authors. Significant yield improvement compared to the control groups was found in all experimental studies. Commercial development of the PGPR inoculants with remarkable biostimulating activities and their successive application should be expanded through collaborative association with different sectors after the removal of existing lacunae. Reading more than 100 articles on various aspects of rhizobacteria, the plan of writing this article has been executed. In this review, we have discussed about the colonization and potency of PGPR strains and how their well‐planned application in agriculture could evidently reinforce the global economy. The main structure of this text is designed as an outline from the development of interrelation between plants and PGPR to the commercialization of PGPR based on their potential role in the field of agriculture. [ABSTRACT FROM AUTHOR]

Biological nitrogen fixation is a fundamental part of ecosystem functioning. Anthropogenic nitrogen deposition and climate change may, however, limit the competitive advantage of nitrogen-fixing plants, leading to reduced relative diversity of nitrogen-fixing plants. Yet, assessments of changes of nitrogen-fixing plant long-term community diversity are rare. Here, we examine temporal trends in the diversity of nitrogen-fixing plants and their relationships with anthropogenic nitrogen deposition while accounting for changes in temperature and aridity. We used forest-floor vegetation resurveys of temperate forests in Europe and the United States spanning multiple decades. Nitrogen-fixer richness declined as nitrogen deposition increased over time but did not respond to changes in climate. Phylogenetic diversity also declined, as distinct lineages of N-fixers were lost between surveys, but the "winners" and "losers" among nitrogen-fixing lineages varied among study sites, suggesting that losses are context dependent. Anthropogenic nitrogen deposition reduces nitrogen-fixing plant diversity in ways that may strongly affect natural nitrogen fixation. [ABSTRACT FROM AUTHOR]

Molybdoenzymes are essential in global nitrogen, carbon, and sulfur cycling. To date, the only known bioavailable source of molybdenum (Mo) is molybdate. However, in the sulfidic and anoxic (euxinic) habitats that predominate in modern subsurface environments and that were pervasive prior to Earth's widespread oxygenation, Mo occurs as soluble tetrathiomolybdate ion and molybdenite mineral that is not known to be bioavailable. This presents a paradox for how organisms obtain Mo to support molybdoenzymes in these environments. Here, we show that tetrathiomolybdate and molybdenite sustain the high Mo demand of a model anaerobic methanogen, Methanococcus maripaludis, grown via Mo-dependent formate dehydrogenase, formylmethanofuran dehydrogenase, and nitrogenase. Cells grown with tetrathiomolybdate and molybdenite have similar growth kinetics, Mo content, and transcript levels of proteins involved in Mo transport and cofactor biosynthesis when compared to those grown with molybdate, implying similar mechanisms of transport and cofactor biosynthesis. These results help to reconcile the paradox of how Mo is acquired in modern and ancient anaerobes and provide new insight into how molybdoenzymes could have evolved prior to Earth's oxygenation. The nitrogen-fixing anaerobic methanogen, Methanococcus maripaludis, can utilize tetrathiomolybdate and molybdenite, previously considered non-bioavailable, as sources of molybdenum for enzymes involved in nitrogen fixation and anaerobic metabolism. [ABSTRACT FROM AUTHOR]

Plasmon-induced photocatalysis showed great potential to improve the photocatalytic nitrogen fixation efficiency, due to the localized surface plasmon resonance effect. The performances of the photocatalytic nitrogen fixation were evaluated by ammonia production rate, apparent quantum efficiency, solar-to-ammonia efficiency, and turnover frequency. The ammonia production rate was compared with three kinds of catalyst, i.e. nano-metals, nano-metal modified semiconductors and highly doped semiconductors. The outstanding contributions of hot electron injection effect, near-field enhancement effect, photothermal effect to nitrogen fixation efficiency were described. The creation of active sites, construct vacancies, and doping regulation were effective methods to prepare high performance catalysts for photocatalytic nitrogen fixation. • Nano-metal-modified semiconductor catalysts achieve ammonia production rate of 785 μmol g−1 h−1. • Highiy doped semiconductors re-define the landscape of photocatalytic NH 3 generation. • The ammonia production rate, apparent quantum efficiency and Solar-to-Ammonia can be used to evaluate the performance ofphotocatalyst. • Hot electron injection effect as a guide for the synthesis of plasma-induced photocatalysts. [ABSTRACT FROM AUTHOR]

The major crop, soybean, forms root nodules with symbiotic rhizobia, providing energy and carbon to the bacteria in exchange for bioavailable nitrogen. The relationship is host-specific and highly host-regulated to maximize energy efficiency. Symbiotic nitrogen fixation (SNF) is greener than synthetic fertilizer for replenishing soil fertility, contributing to yield increase. Nodulation Outer Protein P (NopP) and NopI of the type 3 secretion system (T3SS) of the rhizobium determine host specificity. Sinorhizobium fredii CCBAU25509 (R2) and CCBAU45436 (R4) have different NopP and NopI variants, affecting their respective symbiotic compatibilities with the cultivated soybean C08 and the wild soybean W05. Swapping the NopP variants between R2 and R4 has been shown to switch their compatibility with C08 with the rj2/Rfg1 genotype. To understand the effects of Nops on host compatibility, analyses on the transcriptomic data of W05 roots and nodules inoculated with S. fredii strains containing Nop variants uncovered many differentially expressed genes related to nodulation and nodule functions, providing important information on the effects of Nops on hosts and nodules. [ABSTRACT FROM AUTHOR]

Symbiotic nitrogen fixation (SNF) in legume-rhizobia serves as a sustainable source of nitrogen (N) in agriculture. However, the addition of inorganic N fertilizers significantly inhibits SNF, and the underlying mechanisms remain not-well understood. Here, we report that inorganic N disrupts iron (Fe) homeostasis in soybean nodules, leading to a decrease in SNF efficiency. This disruption is attributed to the inhibition of the Fe transporter genes Natural Resistance-Associated Macrophage Protein 2a and 2b (GmNRAMP2a&2b) by inorganic N. GmNRAMP2a&2b are predominantly localized at the tonoplast of uninfected nodule tissues, affecting Fe transfer to infected cells and consequently, modulating SNF efficiency. In addition, we identified a pair of N-signal regulators, nitrogen-regulated GARP-type transcription factors 1a and 1b (GmNIGT1a&1b), that negatively regulate the expression of GmNRAMP2a&2b, which establishes a link between N signaling and Fe homeostasis in nodules. Our findings reveal a plausible mechanism by which soybean adjusts SNF efficiency through Fe allocation in response to fluctuating inorganic N conditions, offering valuable insights for optimizing N and Fe management in legume-based agricultural systems. Symbiotic nitrogen fixation is a tightly regulated process serving as a sustainable source of nitrogen (N) in agriculture. Here it is shown that external N sources precisely regulate N fixation efficiency by modulating iron transport in nodules of legumes. [ABSTRACT FROM AUTHOR]

The activation of N₂ under mild conditions remains a significant challenge in chemistry. Understanding how the composition of ligands modulates the reactivity of metal centers is pivotal for the rational design of efficient catalysts for nitrogen fixation. Herein, the reactions between polynuclear niobium oxynitride anions Nb4N5‐xOx− (x=0–5) and N2 were investigated by employing mass spectrometry, photoelectron imaging spectroscopy, and theoretical calculations. The rate constants of Nb4N5‐xOx−/N2 gradually decrease for x=0 to x=4, and then increase again for x=5. The sharp increase of the rate constants of Nb4O5−/N2 corresponds to a decrease in the electron detachment energy of the Nb4O5− cluster in the photoelectron spectroscopic experiments. Theoretical calculations suggest that the low‐coordinated Nb−Nb sites in Nb4N5‐xOx− (x=0–5) behaves as the active centers to bind N2 in the side‐on/end‐on manner. Mechanistic analysis reveals that reducing the N/O ratio leads to higher electron densities on the active Nb−Nb centers and decreased positive charge on the metal atoms, which hinders the approach of N2 to the clusters. This finding discloses fundamental insights into the impact of N/O ratio in fine‐tuning the reactivity of metal centers toward N2 adsorption in related catalytic processes. [ABSTRACT FROM AUTHOR]

Soil salinization is currently one of the main abiotic stresses that restrict plant growth. Plant endophytic bacteria can alleviate abiotic stress. The aim of the current study was to isolate, characterize, and assess the plant growth-promoting and saline and alkaline stress-alleviating traits of Peribacillus simplex M1 (P. simplex M1) isolates from maize. One endophytic bacterial isolate, named P. simplex M1, was selected from the roots of maize grown in saline–alkali soil. The P. simplex M1 genome sequence analysis of the bacteria with a length of 5.8 Mbp includes about 700 genes that promote growth and 16 antioxidant activity genes that alleviate saline and alkaline stress. P. simplex M1 can grow below 400 mM NaHCO3 on the LB culture medium; The isolate displayed multiple plant growth-stimulating features, such as nitrogen fixation, produced indole-3-acetic acid (IAA), and siderophore production. This isolate had a positive effect on the resistance to salt of maize in addition to the growth. P. simplex M1 significantly promoted seed germination by enhancing seed vigor in maize whether under normal growth or NaHCO3 stress conditions. The seeds with NaHCO3 treatment exhibited higher reactive oxygen species (ROS) levels than the maize in P. simplex M1 inoculant on maize. P. simplex M1 can colonize the roots of maize. The P. simplex M1 inoculant plant increased chlorophyll in leaves, stimulated root and leaf growth, increased the number of lateral roots and root dry weight, increased the length and width of the blades, and dry weight of the blades. The application of inoculants can significantly reduce the content of malondialdehyde (MDA) and increase the activity of plant antioxidant enzymes (Catalase (CAT), Superoxide Dismutase (SOD), and Peroxidase (POD)), which may thereby improve maize resistance to saline and alkaline stress. Conclusion: P. simplex M1 isolate belongs to plant growth-promoting bacteria by having high nitrogen concentration, indoleacetic acid (IAA), and siderophore, and reducing the content of ROS through the antioxidant system to alleviate salt alkali stress. This study presents the potential application of P. simplex M1 as a biological inoculant to promote plant growth and mitigate the saline and alkaline effects of maize and other crops. [ABSTRACT FROM AUTHOR]

Tillandsia recurvata is an epiphytic plant commonly found in tropical regions and colonizes tree trunks, fences, and power wires. This plant plays an important role in interacting with trees, sharing microorganisms, and performing specific functions in the process of tree colonization. The objective of this study was to evaluate and compare the microbiomes of T. recurvata collected from two different locations (trees and fences) and two plant tissues (leaves and roots). The hypothesis of this study was that the microbiome of T. recurvata is composed of microorganisms that would provide nutritional support to compensate for the lack of nutrients in a particular growth support. The results showed significant differences in microbial diversity between trees and fences, with trees exhibiting higher richness and more complex microbial networks. Proteobacteria was the most prevalent bacterial phylum, with Actinobacteria and Sphingomonas also playing key roles in nitrogen fixation and plant growth. Fungal communities were similar across locations, with Ascomycota and Basidiomycota being predominant, but Paraconiothyrium and Nigrospora showed significant differences in abundance between trees and fences. Functional analysis indicated similar metabolic profiles across leaf and root samples, with key functions for T. recurvata including carbohydrate and amino acid metabolism, stress control, and biofertilization. [ABSTRACT FROM AUTHOR]

Wheat represents a fundamental component of the diet that contributes to ensuring global food security. However, its cultivation faces various abiotic and biotic constraints that result in fluctuating yields. The use of plant growth promoting rhizobacteria (PGPR) with the ability to solubilize phosphate presents itself as an environmentally friendly solution aimed to at enhancing sustainable agriculture practices. The objective of the present study is to assess the potential of PGPR in augmenting both yield and phosphorus (P) levels in wheat plants (Triticum durum L). under semi-controlled environmental conditions. Initially, the strains under investigation were screened for their capacity to dissolve different forms of mineral complex P, along with other plant growth promoting attributes such as iron chelation, Indole acetic acid (IAA) production, nitrogen fixation, and production of exopolysaccharides. Plant response to inoculation with PGPR was studied through an experiment conducted in a greenhouse involving four distinct treatments: (1) Control plants without any inoculation, (2) Inoculation with the PGP27 strain (Rahnella aquatilis), (3) Inoculation with the PGP25 strain (Erwinia persicina), and (4) Inoculation with the PGP374 strain (Raoultella terrigena). Results demonstrated that the studied strains exhibited significant promoting activities, including the solubilization of complex phosphate, the production of exopolysaccharides, IAA, siderophores, and atmospheric nitrogen fixation. Furthermore, the inoculation of plants with PGPR led to an increase in both biomass and plant phosphate concentrations, surpassing those observed in the control group. In conclusion, the findings propose that species like Raoultella and Erwinia have the potential to offer agronomic advantages as rhizobacteria that promote plant growth. [ABSTRACT FROM AUTHOR]

A novel bimetallic CoMoB-coupled carbon nitride with dual moiety defects (CN-TH 3/3) Schottky junction photocatalyst (CoMoB/CN-TH 3/3) was designed for photocatalytic nitrogen fixation. [Display omitted] • A novel CoMoB/(CN-TH 3/3) Schottky junction photocatalyst was designed for photocatalytic NRR. • Both of the intralayer exciton characteristics and the visible light adsorption capacity were altered. • The synergistic effect of CoMoB and CN-TH 3/3 accelerated charge transfer and enhanced the N 2 adsorption and activation. • The photocatalytic NRR performance of optimum CoMoB/CN-TH 3/3 is 6.2 times higher than CN. The sustainable generation of ammonia by photocatalytic nitrogen fixation under mild conditions is fascinating compared to conventional industrial processes. Nevertheless, owing to the low charge transfer efficiency, the insufficient light absorption capacity and limited active sites of the photocatalyst cause the difficult adsorption and activation of N 2 molecules, thereby resulting in a low photocatalytic conversion efficiency. Herein, a novel bimetallic CoMoB nanosheets (CoMoB) co-catalyst modified carbon nitride with dual moiety defects (CN-TH 3/3) Schottky junction photocatalyst is designed for photocatalytic nitrogen reduction reaction (NRR). The photocatalytic nitrogen reduction rate of the optimized CoMoB/CN-TH 3/3 photocatalyst is 4.81 mM·g−1·h−1, which is 6.2 and 2.2 times higher than carbon nitride (CN) (0.78 mM·g−1·h−1) and CN-TH 3/3 (2.21 mM·g−1·h−1), respectively. The excellent photocatalytic NRR performance is ascribed not only to the introduction of dual moiety defects (cyano and cyanamide groups) that extends the visible light absorption range and promotes exciton polarization dissociation, but also to the formation of interfacial electric field between CoMoB and CN-TH 3/3 , which effectively facilitates the interfacial charge transfer. Thus, the synergistic interaction between CN-TH 3/3 and CoMoB further increases the electron numble of CoMoB active sites, which effectively strengthens the adsorption and activation of N 2 and weakens the N N triple bond, thereby enhancing the photocatalytic NRR activity. This work highlights the introduced dual moiety defects and bimetallic CoMoB co-catalyst to synergistically enhance the photocatalytic nitrogen reduction performance. [ABSTRACT FROM AUTHOR]

Land use changes soil microbial and chemical properties, but the mechanism of biological nitrogen fixation under different land use patterns is rarely reported, so we used four types of soil: Natural forest soil (NS), healthy banana soil (HS), diseased banana soil (DS) and paddy soil (PS). Treatments included the control (CK), addition of glucose (G), addition of glucose and ammonium nitrate (GN), addition of banana straw (BS), addition of banana straw and ammonium nitrate (BSN), addition of banana root (BR), and addition of banana root and ammonium nitrate (BRN). The study found that the change of soil utilization types, glucose addition increased carbon dioxide emissions (Compared with the control, increased by 963.11%, 508.39%, 794.77% and 511.34%, respectively) and enhanced the ability of soil microbial nitrogen fixation. Importantly, natural forest soil microorganisms have a higher biological nitrogen fixation capacity compared to other types of soils. Glucose addition caused the accumulation of ammonium nitrogen (Compared with the control, increased by 426.08%, 934.21%, 420% and 1065.95%, respectively), indicating that microorganisms had higher utilization efficiency of soluble carbon and enhanced the biological nitrogen fixation capacity, and nitrogen addition caused the accumulation of ammonium nitrogen, thereby weakening the biological nitrogen fixation capacity. At the same time, glucose significantly increased the Fimicutes phylum (83.73%, 66.38%, 67.18% and 70.36%) and lowered the level of other bacterial phylums, thereby reducing the bacterial network structure, and the stability of the soil environment has decreased. Forest analysis showed that CO2 was an important factor in predicting the bacterial community structure of different soil types, an increase in CO2 content can predict drastic changes in the bacterial community. Bacteria at the Fimicutes phylum level preferred glucose, which may also have a negative effect on bacteria at the level of other phylums. [ABSTRACT FROM AUTHOR]

In this study, the effectiveness of an inoculant containing a nitrogen (N)-fixing microorganism (Methylobacterium symbioticum) was evaluated on maize (Zea mays L.) grown both in the field (silage maize) and in pots over two years (2021 and 2022). The field trial included the following two treatments: with (Yes) and without (No) the inoculant. The pot experiment was designed as a factorial arrangement with two factors: the application of the inoculant (Yes and No) and N applied to the soil (0, 0.4, 0.8, and 1.6 g pot−1). In the field, total dry matter yield (DMY) did not differ significantly between treatments, although the average DMY was higher in the inoculant treatment. In pots, the total DMY varied significantly across all N rates but was only significantly affected by the inoculant application in 2022. N fixation estimates in the field were 58.8 and 14.5 kg ha−1 for 2021 and 2022, respectively, representing 23.7% and 9.1% of the N recovered in the aboveground plant parts. In pots, the estimated fixed N values were −49.2 and 199.2 mg pot−1 in 2021 and 2022, respectively, which corresponded to −5.2% and 18.5% of the N found in the aboveground plant parts. Considering the average values obtained across the four cultivation conditions, there was a positive outcome for the treated plants. However, these values cannot be considered significant when compared to nitrogen removal in maize crops. A commercial product should provide an unequivocal and quantitatively relevant contribution to plant nutrition, which did not appear to be the case. Thus, for this inoculant to provide reliable guarantees of positive outcomes for farmers and become a useful tool in promoting more sustainable agriculture, further studies appear necessary. These studies should aim to determine in which crops and under what cultivation conditions the application of the inoculant is truly effective in enhancing N fixation and improving crop productivity. [ABSTRACT FROM AUTHOR]

Vicia sativa L., commonly known as the common vetch, is an annual, self-pollinating legume used primarily as fodder both by livestock and wildlife. Additionally, it contributes to environmental balance through nitrogen fixation and the improvement of soil properties. The phenotypic, genetic, and metabolite variability among four advanced lines (BK45, BK29, BK23, BK27) and two commercial varieties (M-6900, BI-65) of V. sativa were evaluated in order to be used for future breeding programs aimed at producing genetically improved varieties. BK45 was the most promising line due to its high genetic polymorphism, but also because it exhibited a significant amount of seed production and high seed quality based on its metabolomics profile. A stepwise multiple regression analysis (MRA) revealed a relationship between SCoT alleles, seed, and biomass yield. Additionally, several statistically significant marker bands linked to metabolites were found using the SCoT marker analysis. Hence, data assessed via MRA may be helpful in marker-assisted breeding programs. Finally, the two commercial varieties can be further exploited in breeding programs due to their high genetic diversity. [ABSTRACT FROM AUTHOR]

A nitrogen-fixing strain designated SG130T was isolated from paddy soil in Fujian Province, China. Strain SG130T was Gram-staining-negative, rod-shaped, and strictly anaerobic. Strain SG130T showed the highest 16S rRNA gene sequence similarities with the type strains Dendrosporobacter quercicolus DSM 1736T (91.7%), Anaeroarcus burkinensis DSM 6283T (91.0%) and Anaerospora hongkongensis HKU 15T (90.9%). Furthermore, the phylogenetic and phylogenomic analysis also suggested strain SG130T clustered with members of the family Sporomusaceae and was distinguished from other genera within this family. Growth of strain SG130T was observed at 25–45 °C (optimum 30 °C), pH 6.0–9.5 (optimum 7.0) and 0–1% (w/v) NaCl (optimum 0.1%). The quinones were Q-8 and Q-9. The polar lipids were phosphatidylserine (PS), phosphatidylethanolamine (PE), glycolipid (GL), phospholipid (PL) and an unidentified lipid (UL). The major fatty acids (> 10%) were iso-C13:0 3OH (26.6%), iso-C17:1 (15.6%) and iso-C15:1 F (11.4%). The genomic DNA G + C content was 50.7%. The average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values between strain SG130T and the most closely related type strain D. quercicolus DSM 1736T (ANI 68.0% and dDDH 20.3%) were both below the cut-off level for species delineation. The average amino acid identity (AAI) between strain SG130T and the most closely related type strain D. quercicolus DSM 1736T was 63.2%, which was below the cut-off value for bacterial genus delineation (65%). Strain SG130T possessed core genes (nifHDK) involved in nitrogen fixation, and nitrogenase activity (106.38 μmol C2H4 g−1 protein h−1) was examined using the acetylene reduction assay. Based on the above results, strain SG130T is confirmed to represent a novel genus of the family Sporomusaceae, for which the name Azotosporobacter soli gen. nov., sp. nov. is proposed. The type strain is SG130T (= GDMCC 1.3312T = JCM 35641T). [ABSTRACT FROM AUTHOR]

The chemical behaviors of alkali and alkaline earth metal hydrides including LiH, KH, MgH2, CaH2, and BaH2 under nitrogen plasma differ significantly from one another, exhibiting an ammonia production trend that contrasts with that observed under thermal conditions. A prominent feature of KH is its ability to facilitate plasma-assisted N2 fixation without generating H2 byproduct, showing high atomic economy in utilization of hydride ions for N2 reduction. [ABSTRACT FROM AUTHOR]

Photocatalytic nitrogen reduction presents a promising technology for environmentally friendly ammonia synthesis under mild conditions. However, the performance of photocatalysts is often hindered by high charge carrier recombination and insufficient adsorption and activation of nitrogen molecules. A novel Bi 12 O 17 Cl 2 /BiOCOOH/Bi 2 MoO 6 heterojunction photocatalyst was successful synthesis through surface ion-exchange technique by potassium chloride. The introduction of Bi-rich Bi 12 O 17 Cl 2 on BiOCOOH/Bi 2 MoO 6 heterojunction not only improves electron transfer efficiency due to the dual type-II heterojunction effect but also facilitates on-site N 2 adsorption and activation for solar ammonia production by promoting oxygen vacancies. The high photocatalytic nitrogen fixation activity of the Bi 12 O 17 Cl 2 /BiOCOOH/Bi 2 MoO 6 was 107.78 μmol g−1 h−1 without any sacrificial agent. DFT calculations indicate that oxygen vacancies serve as the active site for adsorbed N 2 , the hydrogenation process preferentially forms on the distal N 2 atom with a lower activation energy about 0.6 eV. Therefore, the combination of oxygen vacancies and band engineering accelerates the production of ammonia. This endeavor holds the potential to unleash the capabilities of engineering for Bi-rich heterojunctions materials with oxygen vacancies, thereby achieving high-efficiency solar-driven N 2 -to-NH 3 conversion in aqueous environments. [Display omitted] • A novel Bi 12 O 17 Cl 2 /BiOCOOH/Bi 2 MoO 6 heterojunction photocatalyst through surface ion-exchange technique by potassium chloride. • The high photocatalytic nitrogen fixation activity of the Bi 12 O 17 Cl 2 /BiOCOOH/Bi 2 MoO 6 was 107.78 μmol g−1 h−1 without any sacrificial agent. • The built-in double type-II heterojunction promotes the on-site N 2 adsorption and activation of vacancy oxygen. [ABSTRACT FROM AUTHOR]

Introduction: Understanding the microbial diversity and potential functional dynamics within the rhizocompartments of Dendrobium huoshanense is crucial for unraveling the plant--microbe interactions that influence its medicinal properties. Methods: This study is the first to characterize the microbiome associated with the rhizocompartments of D. huoshanense, including its cultivation medium, rhizosphere, rhizoplane, and root endosphere, using high-throughput sequencing and subsequent bioinformatic analysis. Results: Bacterial phylogenetic diversity was significantly higher in the endosphere than in the rhizosphere, while fungal α-diversity significantly decreased from the cultivation medium to the endosphere. Both bacterial and fungal niche widths decreased from the cultivation medium to the endosphere. β-Diversity analysis revealed distinct spatial patterns in both bacterial and fungal communities across the rhizocompartments, with the most pronounced differences between the cultivation medium and the endosphere. Taxonomically, Proteobacteria and Ascomycota were predominant in the endosphere for bacterial and fungal communities, respectively. Functional predictions showed significant enrichment of pathways related to xenobiotics biodegradation, lipid metabolism, and nitrogen fixation in the endosphere, while functions associated with plant pathogens and saprotrophs were significantly reduced. Discussion: The results indicate a shift from generalist to specialist microbes from the cultivation medium to the endosphere, suggesting that D. huoshanense exerts strong selective pressure for endophytic fungi. Interestingly, a high proportion of fungi with unknown functions were found in the endosphere, highlighting an area for further research regarding the medicinal efficacy of D. huoshanense. Overall, this study provides foundational data for understanding the adaptive evolution of these microbial communities in response to specific microhabitats. [ABSTRACT FROM AUTHOR]

In this study, hydrolysis precipitation was employed to quickly and efficiently synthesize Cu2+ doped BiOCl nanosheets. The doping of Cu2+promoted the generation of oxygen vacancies on the surface of BiOCl and the separation of photogenerated electron hole pairs. Oxygen vacancies, as electron donor centers and reactive sites, can effectively enhance the catalytic performance of BiOCl. According to performance testing, the nitrogen fixation ability of 3 wt % Cu/BiOCl (259 μmol L–1 h–1) is 1.7 times that of BiOCl (156 μmol L–1 h–1). This synthesis technique provides a novel approach for the inexpensive, effective, and high-yield production of photocatalysts. [ABSTRACT FROM AUTHOR]

Endophytic fungi inhabit various plant tissues and organs without inducing evident disease symptoms. They can contribute positively to the growth of plants, bolster plants resilience to environmental and biological stresses, and facilitate the accumulation of secondary metabolites. These microbial resources possess significant developmental and utilization value in various applications. Hence, this study focused on exploring the plant growth-promoting (PGP) traits of 14 endophytic fungi from Ligusticum chuanxiong Hort (CX) and elucidating the effects and mechanisms that facilitate plant growth. According to PGP activity evaluation, the majority of strains demonstrated the capacity to produce IAA (78.57%), siderophores (50.00%), ammonia (35.71%), potassium solubilization (21.43%), nitrogen fixation (57.14%), and phosphate solubilization (42.86%). Further investigations indicated that the levels of IAA ranged from 13.05 to 301.43 μg/mL, whereas the soluble phosphorus levels ranged from 47.32 to 125.95 μg/mL. In cocultivation assays, it was indicated that Fusarium sp. YMY5, Colletotrichum sp. YMY6, Alternaria sp. ZZ10 and Fusarium sp. ZZ13 had a certain promoting effect on lateral root number and fresh weight of tobacco. Furthermore, ZZ10 and ZZ13 significantly enhanced the germination potential, germination index, and vigor index of tobacco seeds. The subsequent potted trials demonstrated that the four endophytic fungi exhibited an enhancement to growth parameters of tobacco to a certain extent. ZZ10 and ZZ13 treatment had the best promotion effect. Inoculation with YMY5 increased the chlorophyll a and total chlorophyll content. ZZ10 and ZZ13 treatment remarkably increased the net photosynthetic rate, soluble sugars and soluble protein content, catalase and peroxidase activities, and lowered malondialdehyde content in tobacco leaves. In addition, YMY5 remarkably elevated superoxide dismutase activities. ZZ13 upregulated the expression of growth-related gene. Among them, ZZ13 had a better growth-promoting effect. In conclusion, these endophytic fungi possessing multi-trait characteristics and the capacity to enhance plant growth exhibit promising potential as biofertilizers or plant growth regulators. [ABSTRACT FROM AUTHOR]

Forest cover is deteriorating rapidly due to anthropogenic causes, making its restoration urgent. Plant growth-promoting bacteria (PGPB) could offer a viable solution to ensure successful reforestation efforts. This study aimed to select bacterial strains with mechanisms that promote plant growth and enhance seedling development. The bacterial strains used in this study were isolated from the rhizosphere and endophyte regions of Pinus montezumae Lamb. and Pinus patula Schl. et Cham., two Mexican conifer species commonly used for reforestation purposes. Sixteen bacterial strains were selected for their ability to produce auxins, chitinase, and siderophores, perform nitrogen fixation, and solubilize inorganic phosphates; they also harbored genes encoding antimicrobial production and ACC deaminase. The adhesion to seeds, germination rate, and seedling response of P. montezumae and P. patula were performed following inoculation with 10 bacterial strains exhibiting high plant growth-promoting potential. Some strains demonstrated the capacity to enhance seedling growth. The selected strains were taxonomically characterized and belonged to the genus Serratia, Buttiauxella, and Bacillus. These strains exhibited at least two mechanisms of action, including the production of indole-3-acetic acid, biological nitrogen fixation, and phosphate solubilization, and could serve as potential alternatives for the reforestation of affected areas. [ABSTRACT FROM AUTHOR]

Biological N2 fixation (BNF) is traced to the Archean. The nitrogen isotopic fractionation composition (δ15N) of sedimentary rocks is commonly used to reconstruct the presence of ancient diazotrophic ecosystems. While δ15N has been validated mostly using organisms grown under present-day conditions; it has not under the pre-Cambrian conditions, when atmospheric pO2 was lower and pCO2 was higher. Here, we explore δ15N signatures under three atmospheres with (i) elevated CO2 and no O2 (Archean), (ii) present-day CO2, and O2 and (iii) future elevated CO2, in marine and freshwater, heterocytous cyanobacteria. Additionally, we augment our data set from literature for more generalized dependencies of δ15N and the associated fractionation factor epsilon (ε = δ15Nbiomass &#8211; δ15NN2) during BNF in Archaea and Bacteria, including cyanobacteria, and habitats. The ε ranges between 3.70&#8240; and &#8722;4.96&#8240; with a mean ε value of &#8722;1.38 ± 0.95&#8240;, for all bacteria, including cyanobacteria, across all tested conditions. The expanded data set revealed correlations of isotopic fractionation of BNF with CO2 concentrations, toxin production, and light, although within 1&#8240;. Moreover, correlation showed significant dependency of ε to species type, C/N ratios and toxin production in cyanobacteria, albeit it within a small range (&#8722;1.44 ± 0.89&#8240;). We therefore conclude that δ15N is likely robust when applied to the pre-Cambrian-like atmosphere, stressing the strong cyanobacterial bias. Interestingly, the increased fractionation (lower ε) observed in the toxin-producing Nodularia and Nostoc spp. suggests a heretofore unknown role of toxins in modulating nitrogen isotopic signals that warrants further investigation. IMPORTANCE Nitrogen is an essential element of life on Earth; however, despite its abundance, it is not biologically accessible. Biological nitrogen fixation is an essential process whereby microbes fix N2 into biologically usable NH3. During this process, the enzyme nitrogenase preferentially uses light 14N, resulting in 15N depleted biomass. This signature can be traced back in time in sediments on Earth, and possibly other planets. In this paper, we explore the influence of pO2 and pCO2 on this fractionation signal. We find the signal is stable, especially for the primary producers, cyanobacteria, with correlations to CO2, light, and toxin-producing status, within a small range. Unexpectedly, we identified higher fractionation signals in toxin-producing Nodularia and Nostoc species that offer insight into why some organisms produce these N-rich toxic secondary metabolites. [ABSTRACT FROM AUTHOR]

Symbiotic nitrogen fixation within nitrogen-fixing clade (NFC) plants is thought to have arisen from a single gain followed by massive losses in the genomes of ancestral non-nodulating plants. However, molecular evidence supporting this model is limited. Here, we confirm through bioinformatic analysis that NODULES WITH ACTIVATED DEFENSE1 (NAD1) is present only in NFC plants and is thus an NFC-specific gene. Moreover, NAD1 was specifically expressed in nodules. We identified three conserved nodulation-associated cis-regulatory elements (NACE1–3) in the promoter of LjNAD1 from Lotus japonicus that are required for its nodule specific expression. A survey of NFC plants revealed that NACE1 and NACE2 are specific to the Fabales and Papilionoideae, respectively, while NACE3 is present in all NFC plants. Moreover, we found that nodule inception (NIN) directly binds to all three NACEs to activate NAD1 expression. Mutation of L. japonicus LjNAD1 resulted in the formation of abnormal symbiosomes with enlarged symbiosome space and frequent breakdown of bacteroids in nodules, resembling phenotypes reported for Medicago truncatula Mtnad1 and Mtnin mutants. These data point to NIN–NAD1 as an important module regulating rhizobial accommodation in nodules. The regulation of NAD1 by NIN in the NFC ancestor represent an important evolutionary adaptation for nodulation. NODULE INCEPTION directly binds the promoter of the nitrogen-fixing clade-specific gene NODULES WITH ACTIVATED DEFENSE1 to regulate rhizobial intracellular accommodation in nodules. [ABSTRACT FROM AUTHOR]

Green ammonia is assumed to be an important part of the European hydrogen economy and one of the most important substrates of chemical industry. The future development of its manufacturing processes can be related to the electrocatalytic studies yielding in the development of the catalytic materials that would effectively break the nitrogen-nitrogen bond to successfully drive the N2RR—a process of molecular nitrogen electroreduction to ammonia. Molecular nitrogen is characterized with strong triple bond energies (942 kJ/mol) which leading into large dissociation energy of N2 (9,76 eV) and also large energy barrier of the first step of triple bond dissociation 410 kJ/mol (4,25 eV). Those large energies makes reduction to ammonia an extremely difficult task. Metal nitrides of d and f block became in interest due to their activity in ammonia production from molecular nitrogen and hydrogen. Practically all the transition elements occurs in one of the four types of crystalline structures: regular, regular face cantered, hexagonal and hexagonal close packed. The reactions of these metals with nitrogen (or ammonia) typically yields in nitride compounds of an identical type of crystalline structure as the initial metal. Dealing with single metal systems, their ternary counterparts and metal–metal nitride heterostructures, the presented review shows that nitrides are promising groups of electrocatalytic materials. Being property-prone to their internal structural features such as non-stoichiometry and correlated concentration of nitrogen vacancies, metal nitrides are a good candidate for joined investigations spanned between electrochemistry, inorganic chemistry and material engineering. [ABSTRACT FROM AUTHOR]

Context: Alpine pastures are seminatural grasslands which play a crucial role in biodiversity conservation, service provisioning, and mountain livestock systems. The soil microbial communities of pasture are fundamental in ecosystem nutrient cycles, but they are relatively underexplored in European Alpine pastures. Aims: We explored the many soil microbial genes encoding key functions in the nitrogen cycle in three historical alpine pastures grazed by dairy cattle, considering different soils, temporal dynamics, and exclusion of cattle grazing for one summer. Methods: 216 samples were collected across four sampling times. The abundance of genetic determinants involved in nitrogen fixation (nifH), nitrification (amoA bacterial and archaeal), and denitrification (nirK and nosZ) were quantified using real-time polymerase chain reaction. Key results: The terminal denitrification nosZ gene was the most sensitive indicator and responded significantly to soil chemical composition and animal grazing. Sampling time affected nitrogen fixation nifH and intermediate denitrification nirK in relation to rainfall cumulation dynamics. The amoA nitrification genes showed high variability but no significant effects from the tested factors. Conclusions: In spite of a general homeostatic trend occurring in these habitats and of the short term analysis, some genes acted as sensitive reporters of soil compositional differences, intraseasonal climatic variations, and grazing disturbance. Implications: A stocking rate of >0.6 livestock units per hectare can be recommended, to combine animal production with conditions that favour complete denitrification, thus potentially reducing the nitrous oxide greenhouse gas emissions. Higher livestock grazing intensity can be withstood by the ecosystem without denitrification-related drawbacks when the preceding 10 days display a cumulated rainfall lower than 22 mm. Soil microbial communities are fundamental for ecosystem nutrient cycles, but they are relatively underexplored in alpine pastures – seminatural grasslands important for mountain livestock systems. We investigated microbial functions related to the nitrogen cycle in three historical alpine pastures for one summer. Microbial nitrogen functions showed a general inertia in respect to soil variation and grazing disturbance. This has ramifications for future improvement of pasture management in mountain livestock systems. [ABSTRACT FROM AUTHOR]