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Santalum album is a commercially important tree for its aromatic heart wood and oil. Establishing S. album seedlings in field is difficult due to its semi parasitic nature. It requires a host to thrive and survive. In this study the C. equisetifolia was selected as host along with nitrogen fixing actinobacteria Frankia for S. album in nursery to understand their relationship. Both S. album and C. equisetifolia seedlings were propagated in nursery and the cultured Frankia in P agar medium was inoculated in C. equisetifolia seedlings. The S. album seedlings were grown in soil along with C. equisetifolia (+/- Frankia). After 120 days, the seedling of S. album was harvested and found improvement in growth and nutrient uptake. S. album seedlings with the host of C. equisetifolia along with Frankia showed significantly improved root length (38.3 cm seedling-1), shoot length (45.2 cm seedling-1), root collar diameter (3.2 cm seedling-1), 14.2 haustorial attachment seedling-1, shoot biomass (1.96 g seedling-1), root biomass (0.72 g seedling-1) and showed lowest root/shoot ratio (0.36). The nutrient contents particularly N was significantly found in S. album seedlings associated with C. equisetifolia + Frankia. The result showed that essential nutrient nitrogen transfer was mediated through the nitrogen fixing bacteria to C. equisetifolia and absorbed by S. album. In conclusion, the combination of C. equisetifolia + Frankia provided suitable host for the growth and biomass improvement in S. album seedlings. [ABSTRACT FROM AUTHOR]

Phosphate-solubilizing and nitrogen-fixing bacteria are crucial in increasing soil fertility and restoring soil properties damaged by salinity and other abiotic environmental factors. The presented study aims to explore and identify the morphological characteristics of phosphate-solubilizing and nitrogen-fixing bacteria in saline soil. This study took place from August until November 2022 in the field and laboratory of the Faculty of Agriculture, Universitas Muhammadiyah Sumatera Utara, Medan, Indonesia. Isolation of potential microbes proceeded to characterize phosphate-solubilizing and nitrogen-fixing bacteria. Sampling began with the soil planted with rice and palm oil at the sampling location. Morphological parameters observed were color, form, margin, surface, and elevation of pure colonies. The result showed that exploring various species in saline soil revealed 19 colonies and 14 cells of phosphate-solubilizing bacteria and 16 colonies and 14 cells of nitrogen-fixing bacteria. The pure colonies of the phosphate-solubilizing and nitrogen-fixing bacteria showed differences in the morphological characteristics, i.e., color, form, margin, surface, and elevation. The potential microbes obtained sought to increase soil fertility and crop production. [ABSTRACT FROM AUTHOR]

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Tropical cloud forests are characterized by abundant and biodiverse mosses which grow epiphytically as well as on the ground. Nitrogen (N)-fixing cyanobacteria live in association with most mosses, and contribute greatly to the N pool via biological nitrogen fixation (BNF). However, the availability of nutrients, especially N and phosphorus (P), can influence BNF rates drastically. To evaluate the effects of increased N and P availability on BNF in mosses, we conducted a laboratory experiment where we added N and P, in isolation and combined, to three mosses (Campylopus sp., Dicranum sp. and Thuidium peruvianum) collected from a cloud forest in Peru. Our results show that N addition almost completely inhibited BNF within a day, whereas P addition caused variable results across moss species. Low N2 fixation rates were observed in Campylopus sp. across the experiment. BNF in Dicranum sp. was decreased by all nutrients, while P additions seemed to promote BNF in T. peruvianum. Hence, each of the three mosses contributes distinctively to the ecosystem N pool depending on nutrient availability. Moreover, increased N input will likely significantly decrease BNF associated with mosses also in tropical cloud forests, thereby limiting N input to these ecosystems via the moss-cyanobacteria pathway. [ABSTRACT FROM AUTHOR]

Seagrass is a significant primary producer of coastal ecosystems; however, the continued degradation of seagrass beds is a serious problem that has attracted widespread attention from researchers. Rhizosphere microorganisms affect seagrass and participate in many life activities of seagrass. This study explored the relationship between the composition of microbes in the rhizosphere and the surrounding environment of Ruppia sinensis by using High-throughput sequencing methods. The dominant bacterial groups in the rhizosphere surface sediments of R. sinensis and the surrounding environment are Proteobacteria, Bacteroidota, and Firmicutes. Moreover, the dominant fungal groups are Ascomycota, Basidiomycota, and Chytridiomycota. Significant differences (p < 0.05) were identified in microbial communities among different groups (rhizosphere, bulk sediment, and surrounding seawater). Seventy-four ASVs (For bacteria) and 48 ASVs (For fungal) were shared among seagrass rhizosphere, surrounding sediment, and seawater. The rhizosphere was enriched in sulfate-reducing bacteria and nitrogen-fixing bacteria. In general, we obtained the rhizosphere microbial community of R. sinensis, which provided extensive evidence of the relative contribution of the seagrass rhizosphere and the surrounding environment. [ABSTRACT FROM AUTHOR]

Azospirillium species are widely used as Biofertilizer to increase crop yield and are free-living nitrogen-fixing bacteria, one of the best-studied plant growth-promoting Rhizobacteria. It is commonly found along with the roots of many different plant species. The present study included the isolation of Azospirillium species from roots and soils in Rhizospheric regions. 50 isolates were isolated from fields in different districts of Saurashtra region in Gujarat against NFB Medium. Significant isolates were isolated from the root surface and root internal tissues. These 50 were morphologically identified and biochemically characterized isolates included the techniques documented in Bergey's Textbook of Identified Bacteria 9th edition (TSI-Triple Sugar Iron, GPB-Glucose Phosphate Broth, MR-Methyl Red VP-Voges Proskauer, TRP-Tryptophan, PNB-Peptone Nitrate Broth, Carbohydrate) out of which fifteen isolates were biochemically positive and were also capable of producing IAA (Indole Acetic Acid), and were also capable of producing IAA. [ABSTRACT FROM AUTHOR]

This study is aimed at adding different types of mature compost and sulfur powder, as additives into food waste composting to investigate the effect on nitrogen loss and compost maturity. The composting experiment used the in-vessel composting method and was conducted continuously for 15 days. High-throughput sequencing was used to analyze the bacterial community during composting. Results showed that the secondary fermentation mature compost mixed with sulfur powder group had the most reduction of ammonia emission (56%) and the primary fermentation mature compost amendments were the most effective for nitrous oxide emission reduction (37%). The temperature, pH, and nitrogen forms of transformation of the pile significantly affect the nitrogen loss during composting. Firmicutes helped to promote the rapid warming of the pile, and Actinobacteria and Proteobacteria played an important role in decomposition of organic matter. Thermobifida and Ureibacillus had a main contribution to the rapid degradation of organic matter in the process of composting. The relative abundance of nitrogen-fixing bacteria was higher, and the relative abundance of predominantly ammonifying and denitrifying bacteria was lower than the control group, with the addition of different additives. [ABSTRACT FROM AUTHOR]

Background: Root-knot nematodes (RKN) are among the most important root-damaging plant-parasitic nematodes, causing severe crop losses worldwide. The plant rhizosphere and root endosphere contain rich and diverse bacterial communities. However, little is known about how RKN and root bacteria interact to impact parasitism and plant health. Determining the keystone microbial taxa and their functional contributions to plant health and RKN development is important for understanding RKN parasitism and developing efficient biological control strategies in agriculture. Results: The analyses of rhizosphere and root endosphere microbiota of plants with and without RKN showed that host species, developmental stage, ecological niche, and nematode parasitism, as well as most of their interactions, contributed significantly to variations in root-associated microbiota. Compared with healthy tomato plants at different developmental stages, significant enrichments of bacteria belonging to Rhizobiales, Betaproteobacteriales, and Rhodobacterales were observed in the endophytic microbiota of nematode-parasitized root samples. Functional pathways related to bacterial pathogenesis and biological nitrogen fixation were significantly enriched in nematode-parasitized plants. In addition, we observed significant enrichments of the nifH gene and NifH protein, the key gene/enzyme involved in biological nitrogen fixation, within nematode-parasitized roots, consistent with a potential functional contribution of nitrogen-fixing bacteria to nematode parasitism. Data from a further assay showed that soil nitrogen amendment could reduce both endophytic nitrogen-fixing bacteria and RKN prevalence and galling in tomato plants. Conclusions: Results demonstrated that (1) community variation and assembly of root endophytic microbiota were significantly affected by RKN parasitism; (2) a taxonomic and functional association was found for endophytic nitrogen-fixing bacteria and nematode parasitism; and (3) the change of nitrogen-fixing bacterial communities through the addition of nitrogen fertilizers could affect the occurrence of RKN. Our results provide new insights into interactions among endophytic microbiota, RKN, and plants, contributing to the potential development of novel management strategies against RKN. -jDL8NUj-q41CTzHNcAR Video Abstract [ABSTRACT FROM AUTHOR]

Host-controlled intracellular accommodation of nitrogen-fixing bacteria is essential for the establishment of a functional Root Nodule Symbiosis (RNS). In many host plants, this occurs via transcellular tubular structures (infection threads - ITs) that extend across cell layers via polar tipgrowth. Comparative phylogenomic studies have identified RPG (RHIZOBIUM-DIRECTED POLAR GROWTH) among the critical genetic determinants for bacterial infection. In Medicago truncatula, RPG is required for effective IT progression within root hairs but the cellular and molecular function of the encoded protein remains elusive. Here, we show that RPG resides in the protein complex formed by the core endosymbiotic components VAPYRIN (VPY) and LUMPY INFECTION (LIN) required for IT polar growth, co-localizes with both VPY and LIN in IT tip- and perinuclear-associated puncta of M. truncatula root hairs undergoing infection and is necessary for VPY recruitment into these structures. Fluorescence Lifetime Imaging Microscopy (FLIM) of phosphoinositide species during bacterial infection revealed that functional RPG is required to sustain strong membrane polarization at the advancing tip of the IT. In addition, loss of RPG functionality alters the cytoskeletonmediated connectivity between the IT tip and the nucleus and affects the polar secretion of the cell wall modifying enzyme NODULE PECTATE LYASE (NPL). Our results integrate RPG into a core host machinery required to support symbiont accommodation, suggesting that its occurrence in plant host genomes is essential to co-opt a multimeric protein module committed to endosymbiosis to sustain IT-mediated bacterial infection. [ABSTRACT FROM AUTHOR]

In the boreal forests, feather mosses such as Hylocomium splendens and Pleurozium schreberi are colonized by cyanobacteria, which provide large amounts of nitrogen to forest ecosystems through nitrogen fixation. Although these feather mosses are also ubiquitous in subalpine forests of East Asia, little is known regarding their associated cyanobacteria and their ability to fix nitrogen. In this study, we investigated (1) whether cyanobacteria co-exist and fix nitrogen in the two species of feather mosses that cover the ground surface in a subalpine forest of Mt. Fuji, (2) whether cyanobacteria belonging to a common cluster with boreal forests are found in feather mosses in Mt. Fuji, and (3) whether moss-associated nitrogen fixation rates differed among moss growing substrates, canopy openness, and moss nitrogen concentrations in the same forest area. Our results showed that cyanobacteria colonized feather mosses in the subalpine forests of Mt. Fuji and acetylene reduction rates as an index of nitrogen fixation tended to be higher in H. splendens than in P. schreberi. Based on analysis of the nifH gene, 43 bacterial operational taxonomic units (OTUs) were identified, 28 of which represented cyanobacteria. Among the five clusters of cyanobacteria classified based on their nifH gene and identified in northern Europe, four (Nostoc cluster I, Nostoc cluster II, Stigonema cluster, and nifH2 cluster) were also found at Mt. Fuji. The acetylene reduction rate differed depending on the moss growing substrate and the total nitrogen concentration of moss shoots, and a strong negative correlation was observed with the total nitrogen concentration. [ABSTRACT FROM AUTHOR]

Farmers usually apply more chemical fertilizers to enhance the yield of strawberries in soilless culture. Humic substances and biofertilizers are now considered essential nutrient sources in sustainable agriculture. The objective of the greenhouse experiment was to observe the effect of humic and fulvic acid (humic substances), and biofertilizer on root growth, nitrogen (N) and phosphor (P) of the growing media, populations of N-fixing and P-solubilizing bacteria in the root zone, and yield of strawberry grown in the cocopeat-based substrate. The experiment was set up in a randomized block design consisting of seven treatments and four replications. The treatments included humic acid, fulvic acid, and biofertilizer in single or combined applications. All data were subjected to analysis of variance and followed by Duncan's Multiple Range Test with p

Bioremediation technology, another strategy known for restoring degraded environments, utilizes beneficial microorganisms, including arbuscular mycorrhizal fungi (AMF) and nitrogen-fixing bacteria (NFB). Despite its potential, the biological processes of these microorganisms in contaminated sites remain poorly understood, hindering effective pollutant toxicity reduction. Establishing a connection between plant root systems and these microorganisms is crucial for enabling plant survival in heavy metal-contaminated soils. Narra (Pterocarpus indicus Willd.), a leguminous plant, typically associates with symbiotic nitrogen-fixing bacteria, forming nodules in the roots. Additionally, Narra forms a symbiotic relationship with AMF, phosphorus-fixing microbes, making it an ideal tree species for rehabilitating mined-out areas. In this study, five microbial biofertilizers, namely: MYKORICH®, MYKOVAM®, newMYC, newNFB, and combined newMYC+newNFB, plus a control were used to test their root colonization potential on Narra seedlings grown in nickel (Ni) and gold (Au) mined-out soils collected from Taganito Mining Corporation (TMC) and Manila Mining Corporation (MMC) in Claver and Placer, Surigao del Norte, Philippines, respectively. The results showed that newMYC had the highest root colonization in Ni mined-out soil, while MYKORICH® excelled in Au mined-out soil. The AMF spore count was highest in MYKORICH® for Ni mined-out soil and newMYC in Au mined-out soil. NFB colonization was highest in newMYC-treated seedlings for Ni mined-out soil and combined newMYC+newNFB for Au mined-out soil. The microbial biofertilizers utilized in this research, such as MY-KORICH®, MYKOVAM, newMYC, newNFB, and combined newNFB and newMYC, naturally occur in the environment and can be easily extracted. This cost-effective characteristic provides an advantage for mining companies seeking treatments for soil amelioration to rehabilitate mined-out areas.

Endophytic bacteria, especially those that participate in nitrogen fixation, play critical roles in supplying essential nutrients for legume plant growth. Despite that there have been numerous investigations targeting bacterial microbiomes in legume roots and nodules, little is known about embryonic bacteria that facilitate plant nutrient utilization after seed germination. Here, we collected and investigated endophytic bacterial microbiome in edible pea (Pisum sativum) embryos using five representative cultivars and a pea sprout (shoot of pea [SHP]) control. Twenty-six nitrogen-fixing bacteria (NFB) were isolated from pea embryos, with three strains found in fresh grain pea (FGP) and snow pea (SP) exhibiting the strongest nitrogenase activity of above 85 nmol C2H4/mL/h. Some NFB isolates are also potassium-solubilizing bacteria (KSB) or phosphorus-solubilizing bacteria (PSB) utilizing inorganic and/or organic phosphorus. All 26 NFB showed variable levels (0.41 to 7.10 μg/mL) of indole-3-acetic acid (IAA) secretion. The nutrient-solubilizing NFB identified in our research are potential targets for biofertilizer development. They could be useful in converting nitrogen, potassium, and/or phosphorus into usable forms for the plants. At the microbiome level, high-throughput 16S ribosomal RNA (rRNA) sequencing of 40 bacterial collections from pea embryos generated 4234 operational taxonomic units (OTUs) using 97% identity as the threshold for clustering high-quality effective reads (valid tags). Analysis of OTU annotation results revealed similar species community structures, abundance, and diversity in most samples. Our embryo-derived endophytic bacterial pool provides a microbiome platform for seed dormancy and germination research of edible peas, as well as for digging new biofertilizer resources in general.

Improved agricultural practices and rapid industrialization have led to huge waste generation, and the management of this waste is becoming a global concern. The process of vermicomposting has emerged as a method of choice for converting waste into useful manure, with evidence of increase in crop productivity. During vermicomposting, the collective activities of decomposing microorganisms and earthworms lead to the humification of organic/inorganic waste, thereby generating the final product called vermicompost. Different types of industrial wastes such as waste from paper industries, tanneries, sugar mills, and pulp and textile industries have been effectively converted to vermicompost and successfully used to improve plant growth. The vermicompost thus formed was also demonstrated to increase the production of pharmaceutically important plant secondary metabolites such as withanolides and polyunsaturated fatty acids. Microbial amendment with different bacterial and fungal strains during vermicomposting further proves to be beneficial by increasing nitrogen content, decomposing organic waste, providing aeration, and stabilizing the vermicompost. These microorganisms after passing through the earthworm’s intestine increase in numbers in the vermicast, thus becoming enriched in vermicompost, which is particularly important for their use as biofertilizers. The precise role of different microbial pretreatments in improving the quality of vermicompost generated from industrial and agricultural waste is, however, not completely understood. To fill this gap in knowledge, the present article aims to review published literature to highlight the potential of microbial amendment during vermicomposting for bioremediation of industrial and agricultural waste. Microbial pre-composting followed by vermicomposting emerges as an ecofriendly and economical approach for managing agricultural and industrial waste.

Nitrogen is an important factor affecting crop yield, but excessive use of chemical nitrogen fertilizer has caused decline in nitrogen utilization and soil and water pollution. Reducing the utilization of chemical nitrogen fertilizers by biological nitrogen fixation (BNF) is feasible for green production of crops. However, there are few reports on how to have more ammonium produced by nitrogen-fixing bacteria (NFB) flow outside the cell. In the present study, the amtB gene encoding an ammonium transporter (AmtB) in the genome of NFB strain Kosakonia radicincitans GXGL-4A was deleted and the △amtB mutant was characterized. The results showed that deletion of the amtB gene had no influence on the growth of bacterial cells. The extracellular ammonium nitrogen (NH4+) content of the △amtB mutant under nitrogen-free culture conditions was significantly higher than that of the wild-type strain GXGL-4A (WT-GXGL-4A), suggesting disruption of NH4+ transport. Meanwhile, the plant growth-promoting effect in cucumber seedlings was visualized after fertilization using cells of the △amtB mutant. NFB fertilization continuously increased the cucumber rhizosphere soil pH. The nitrate nitrogen (NO3−) content in soil in the △amtB treatment group was significantly higher than that in the WT-GXGL-4A treatment group in the short term but there was no difference in soil NH4+ contents between groups. Soil enzymatic activities varied during a 45-day assessment period, indicating that △amtB fertilization influenced soil nitrogen cycling in the cucumber rhizosphere. The results will provide a solid foundation for developing the NFB GXGL-4A into an efficient biofertilizer agent. [ABSTRACT FROM AUTHOR]

Background: Azotobacter vinellandii is a soil bacterium which fixes atmospheric nitrogen and provides growth hormones to plant. Locally isolated species can be utilized and efficient bio fertilizers can be prepared. Methods: A nitrogen fixing bacteria was isolated and it was biochemically identified as Azotobacter vinellandii and named as Azotobacter vinellandii SINAz1. The 16s rRNA was isolated and the sequence was submitted to NCBI data base and got the Accession number as MN135308.1. The presence of nif D, nif K and nif H gene was studied by PCR amplification. The nitrogen fixing efficiency of these bacteria was studied in laboratory by acetylene reduction assay (ARA) and also by pot culture experiments. The plant growth promoting (PGP) activities also studied by isolating and estimating the secretion of hormones like IAA, GA3, ABA and zeatin. These bacteria also provide salinity stress (200 mM NaCl) tolerance to rice plant for 15 days as compared with the control. Result: The phenotypic growth and yield of rice crop by the application of these bacteria was studied which found to be significantly better than the control. This novel bacterium can be used as a substitute for the chemically synthesized nitrogen fertilizer for better productivity under normal as well as salinity stress condition. [ABSTRACT FROM AUTHOR]

This study determined the influence of varying soil amendments containing bamboo biochar (BB) with or without biofertilizers on the populations of arbuscular mycorrhizal fungi (AMF) and nitrogen-fixing bacteria (NFB), on plant growth, and soil parameters in acidic soil under nursery conditions. Cacao var. UF18 were sown in polypropylene bags filled with a 200-g ovensterilized soil-sand mixture. After a month, cacao seedlings were transferred to a mixture of unsterilized acidic soil (4.65 pH) and vermicompost (3:1, w/w) and amended with BB (w/w) at varying concentrations (0, 15, and 30%). Inoculation with available formulated AMF inoculants (AMF1 and AMF2) and NFB, singly and in combination, was also done during this stage by adding the recommended rates directly beneath the roots. The results showed that regardless of biochar concentration and the type of AMF inoculum used, there was a significant decrease in AMF spore count and root colonization when AMF and NFB were combined. Root colonization in cacao by AMF1 or AMF2 showed no significant difference from each other. In general, the amendment of BB could have resulted in better soil properties such as increased pH, nitrogen (N), and phosphorus (P), which provided a condition where microorganisms can optimally grow. However, co-inoculation of AMF and NFB resulted in a decrease in both spore count and root colonization, suggesting possible adverse interaction between the microorganisms. Co-amendment of 15% BB and biofertilizer (NFB or AMF1 alone) resulted in heavier (140 and 130 g plant-1) plant biomass compared with single inoculation of BB or biofertilizer (50-90 g plant-1). Moreover, the highest N uptake (2257 mg plant-1) was observed in cacao plants inoculated with NFB grown in 15% BB-amended soil. Cacao seedlings inoculated with NFB and AMF1 and amended with 15% BB soil resulted in the highest uptake of P (537 and 539 mg plant-1, respectively). The results clearly showed the beneficial effects of combining biofertilizer and BB at 15% concentration as compared to 0 and 30%. It is recommended that the same treatments be done in a field study to verify the results obtained in the nursery experiments. [ABSTRACT FROM AUTHOR]

Background: Sugarcane growth and yield are complex biological processes influenced by endophytic nitrogen-fixing bacteria, for which the molecular mechanisms involved are largely unknown. In this study, integrated metabolomic and RNA-seq were conducted to investigate the interaction between an endophytic bacterial strain, Burkholderia GXS16, and sugarcane tissue culture seedlings. Results: During treatment, the colonization of GXS16 in sugarcane roots were determined, along with the enhanced activities of various antioxidant enzymes. Accordingly, 161, 113, and 37 differentially accumulated metabolites (DAMs) were found in the pairwise comparisons of adjacent stages. In addition, transcriptomic analyses obtained 1,371 (IN-vs-CN), 1,457 (KN-vs-IN), and 365 (LN-vs-KN) differentially expressed genes (DEGs), which were mainly involved in the pathways of glutathione metabolism and carbon metabolism. We then assessed the pattern of metabolite accumulation and gene expression in sugarcane during GXS16 colonization. The results showed that both DAMs and DGEs in the upregulated expression profiles were involved in the flavonoid biosynthesis pathway. Overall, p-coumaroyl-CoA in sugarcane roots transferred into homoeriodictyol chalcone and 5-deoxyleucopelargonidin due to the upregulation of the expression of genes shikimate O-hydroxycinnamoyltransferase (HCT), chalcone synthase (CHS), and phlorizin synthase (PGT1). Conclusions: This study provides insights into the gene regulatory mechanisms involved in the interaction between GXS16 and sugarcane roots, which will facilitate future applications of endophytic nitrogen-fixing bacteria to promote crop growth. [ABSTRACT FROM AUTHOR]

Understanding the composition and activation of multicomponent receptor complexes is a challenge in biology. To address this, we developed a synthetic approach based on nanobodies to drive assembly and activation of cell surface receptors and apply the concept by manipulating receptors that govern plant symbiosis with nitrogen-fixing bacteria. We show that the Lotus japonicus Nod factor receptors NFR1 and NFR5 constitute the core receptor complex initiating the cortical root nodule organogenesis program as well as the epidermal program controlling infection. We find that organogenesis signaling is mediated by the intracellular kinase domains whereas infection requires functional ectodomains. Finally, we identify evolutionarily distant barley receptors that activate root nodule organogenesis, which could enable engineering of biological nitrogen-fixation into cereals. [ABSTRACT FROM AUTHOR]

Our knowledge of microbial biogeography has advanced in recent years, yet we lack knowledge of the global diversity of some important functional groups. Here, we used environmental DNA from 327 globally collected soil samples to investigate the biodiversity patterns of nitrogen-fixing bacteria by focusing on the nifH gene but also amplifying the general prokaryotic 16S SSU region. Globally, N-fixing prokaryotic communities are driven mainly by climatic conditions, with most groups being positively correlated with stable hot or seasonally humid climates. Among soil parameters, pH, but also soil N content were most often shown to correlate with the diversity of N-fixer groups. However, specific groups of N-fixing prokaryotes show contrasting responses to the same variables, notably in Cyanobacteria that were negatively correlated with stable hot climates, and showed a U-shaped correlation with soil pH, contrary to other N-fixers. Also, the non-N-fixing prokaryotic community composition was differentially correlated with the diversity and abundance of N-fixer groups, showing the often-neglected impact of biotic interactions among bacteria. [ABSTRACT FROM AUTHOR]

Nitrogen–fixing bacteria execute biological nitrogen fixation through nitrogenase, converting inert dinitrogen (N2) in the atmosphere into bioavailable nitrogen. Elaborating the molecular mechanisms of orderly and efficient biological nitrogen fixation and applying them to agricultural production can alleviate the "nitrogen problem". Azotobacter vinelandii is a well–established model bacterium for studying nitrogen fixation, utilizing nitrogenase encoded by the nif gene cluster to fix nitrogen. In Azotobacter vinelandii, the NifA–NifL system fine–tunes the nif gene cluster transcription by sensing the redox signals and energy status, then modulating nitrogen fixation. In this manuscript, we investigate the transcriptional regulation mechanism of the nif gene in autogenous nitrogen–fixing bacteria. We discuss how autogenous nitrogen fixation can better be integrated into agriculture, providing preliminary comprehensive data for the study of autogenous nitrogen–fixing regulation. [ABSTRACT FROM AUTHOR]

Pot experiments were conducted to explore the effects of different rice straw returning soil on the community structure and function of bacteria in rice root, rhizosphere, leaf and phyllosphere under 7 conditions of rice straw combined with different fertilizers respectively. The results showed that: rice straw returning in different ways increased the content of soil pH and K, and reduced the accumulation of N, P and organic matter in soil, and different rice straw returning ways had different effects; rice straw returning reduced dry weight of rice grain, 2% of rice straw returning reduced rice grain greater than that of 1% rice straw returning; The reduction of NP combined fertilization is greater than that of NK combined fertilization and NPK combined fertilization. Except for the decrease of chao_1 index in rice root at maturity, rice straw returning significantly improved the abundance, diversity and evenness of bacteria in rice root, rhizosphere, leaf and phyllosphere. Rice straw returning increased the content of REEs in rice, and 2% of rice straw returning soil increased rare earth element (REE) content in rice grain greater than that of 1% rice straw returning soil. Different ways of rice straw returning soil reduced the abundance of Bacillus, while the abundance of Exiguobacterium in rice leaves was hundreds of times higher than that of the control group, and the genus in leaves was dozens of times higher than that of the control group, 2% of rice straw returning soil increased the abundance of harmful bacteria and pathogens of Acidovorax, Clostridium sensu stricto, Citrobacter, Curtobacterium, and 1% of rice straw returning soil promoted the abundance of nitrogen fixing bacteria, plant growth-promoting bacteria, stress resistant bacteria such as Lactobacillus, Azospira, Acinetobacter, Bradyrhizobium and Acidocella; Environmental factors such as available P, organic matter, total nitrogen, nitrate nitrogen, rare earth element content in rice roots, available K and soil moisture are important factors affecting the community structure of bacteria in rice roots, rhizosphere, leaf and phyllosphere at tillering stage of the rice. pH, REE content in rice roots, shoots, organic matter, total nitrogen, nitrate nitrogen and soil moisture content are the main environmental factors affecting the community structure of bacteria in rice roots, rhizosphere, leaf and phyllosphere at maturity stage of rice. 2% rice straw returning soil promoted the formation of harmful bacteria, which may be an important reason for its significant reduction in the dry weight of rice grains. [ABSTRACT FROM AUTHOR]

Chemical nitrogen fixation by the Haber-Bosch method permitted industrial-scale fertilizer production that supported global population growth, but simultaneously released reactive nitrogen into the environment. This minireview highlights the potential for bacterial nitrogen fixation and mitigation of greenhouse gas (GHG) emissions from soybean and rice fields. Nitrous oxide (N2O), a GHG, is mainly emitted from agricultural use of nitrogen fertilizer and symbiotic nitrogen fixation. Some rhizobia have a denitrifying enzyme system that includes an N2O reductase and are able to mitigate N2O emission from the rhizosphere of leguminous plants. Type II methane (CH4)-oxidizing bacteria (methanotrophs) are endophytes in paddy rice roots and fix N 2 using CH4 (a GHG) as an energy source, mitigating the emission of CH4 and reducing nitrogen fertilizer usage. Thus, symbiotic nitrogen fixation shows potential for GHG mitigation in soybean and rice fields while simultaneously supporting sustainable agriculture. [ABSTRACT FROM AUTHOR]

Biosurfactants are metabolites produced by microorganisms during their growth and reproduction. They are amphiphilic molecules capable of modifying surface and interfacial tension. A petrophilic, nitrogen-fixing, phosphorus-solubilizing, and biosurfactant-producing bacterial strain was isolated and characterized. The isolated strain was cultivated in Kim medium with a C:N ratio of 2:1, from which its growth kinetics was determined. Samples of the culture broth were taken at different times and the collapsed drop, oil dispersion and emulsification index tests were performed. Maximum culture growth occurred at 72 h. The biosurfactant was extracted from the crude cell-free broth using a mixture of solvents and a yield of 2.21 g/L was obtained. Thin-layer chromatography and FT-IR analyzes revealed the presence of a lipopeptide biosurfactant. Tensiometry tests showed that the biosurfactant was able to lower the surface tension of water from 72 mN/m to 40 mN/m and the critical micelle concentration was 0.058 (w/w). Probit analysis for toxicity determination showed that there was no weight loss in Eisenia foetida specimens in a range between 10000 and 50000 ppm. [ABSTRACT FROM AUTHOR]

Ammonia is an important chemical that is widely used in fertilizer applications as well as in the steel, chemical, textile, and pharmaceutical industries, which has attracted attention as a potential fuel. Thus, approaches to achieve sustainable ammonia production have attracted considerable attention. In particular, biological approaches are important for achieving a sustainable society because they can produce ammonia under mild conditions with minimal environmental impact compared with chemical methods. For example, nitrogen fixation by nitrogenase in heterogeneous hosts and ammonia production from food waste using microorganisms have been developed. In addition, crop production using nitrogen-fixing bacteria has been considered as a potential approach to achieving a sustainable ammonia economy. This review describes previous research on biological ammonia production and provides insights into achieving a sustainable society. [ABSTRACT FROM AUTHOR]

During the course of plant evolution, leguminous and a few plants species have established root nodule symbiosis (RNS), one of the nitrogen nutrient acquisition strategies based on mutual interaction between plants and nitrogen-fixing bacteria. In addition to its useful agronomic trait, RNS comprises a unique form of plant lateral organogenesis; dedifferentiation and activation of cortical cells in the root are induced upon bacterial infection during nodule development. In the past few years, the elucidations of the significance of NODULE INCEPTION transcription factor as a potentially key innovative factor of RNS, the details of its function, and the successive discoveries of its target genes have advanced our understanding underlying molecular mechanisms of nodule organogenesis. In addition, a recent elucidation of the role of legume SHORTROOT-SCARECROW module has provided the insights into the unique properties of legume cortical cells. Here, I summarize such latest findings on the neofunctionalized key players of nodule organogenesis, which may provide clue to understand an evolutionary basis of RNS. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Northwest A & F University - Natural Science Edition is the property of Editorial Department of Journal of Northwest A&F University (Natural Science Edition) 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.)

Background and aims: Straw amendment can increase nitrogen fixation in paddy field, however, the efficiency of carbon sources with different biochemical properties to enhance N2 fixation and nitrogen fixation activity is still unclear. Methods: A 15N2-labelling system was used in the field environment to determine biological nitrogen fixation (BNF) under the addition of three kinds of straw. The nifH gene (DNA) and nifH RNA gene (cDNA) of soil were amplified by real-time fluorescent quantitative PCR. The diversity and community composition of nitrogen fixing microorganisms were studied by high-throughput sequencing. The study is expected to reveal how different carbon sources impact biological nitrogen fixation and its mechanism in the paddy field system. Results: Results showed that the absolute abundance diazotrophs in the treatment of mature stage wheat straw (MWS) was 4.88 times as high as that in the CK treatment, but jointing stage wheat straw (JWS) and poplar branch (PB) did not induce any significant changes. Straw amendment had no impact on cyanobacteria abundance. The proportion of N2 fixation increased by MWS was 2.07 times, but which was much lower than the increase proportion of the heterotrophic diazotrophs, leading to a decrease of diazotrophic nitrogen fixation activity. Conclusions: Mature wheat straw addition increased biologically fixed nitrogen in paddy field by increasing the number of heterotrophic nitrogen fixing bacteria. The results indicated that to increase biological N2 fixation in paddy system, straws with low nitrogen content and high C/N ratio were recommended. [ABSTRACT FROM AUTHOR]

Microorganisms are essential parts of soil and play an important role in mediating many processes and influencing plant health. Arbuscular mycorrhizal fungi (AMF) and nitrogen-fixing bacteria (NFB), the most common of such microorganisms, can benefit plants by enhancing the nutrient-absorbing ability of roots through bio-inoculation, also called biofertilization. Different methods have been tested and proven to be effective in the enhancement of soil nutrient availability. However, the effects of increased application of biological methods with minimal chemical fertilizers are still inconsistent. In this 2-year of fixed-point greenhouse test, we aimed to evaluate the impact of AMF (Rhizophagus irregularis) and/or NFB (Azotobacter) on growth, quality, and yield of eggplants under different N levels. Data showed that biofertilizer application with reduced chemical fertilizer had the highest impact on eggplant performance and yield. Indeed, low chemical fertilizers combined with adequate amounts of biofertilizers produced a higher plant height, length and width of leaves, dry matter, number of fruits per plant with better morphology, total yield per plant, and total soluble solids (TSS), suggesting that the use of Azotobacter and R. irregularis as biofertilizers could substantially reduce the use of chemical fertilizers without impairing the quality and yield of eggplant. [ABSTRACT FROM AUTHOR]

Recent studies have described active nitrogen fixation in high‐latitude waters, but the ecological controls on the occurrence or activity of nitrogen‐fixing organisms (diazotrophs) in such systems remain unknown. Turnover rates and top‐down controls are also general knowledge gaps for marine diazotrophs. We detected abundant UCYN‐A (endosymbiotic nitrogen‐fixing cyanobacteria) in the Gulf of Anadyr, western Bering Sea, which correlated with high dissolved iron to dissolved inorganic nitrogen ratios (Fe : DIN) due to riverine input. Growth and grazing mortality of UCYN‐A sublineages were almost balanced with higher biomass‐turnover rates compared to the whole phytoplankton community, indicating selective grazing of UCYN‐A in nitrogen‐depleted waters. Grazing rates on UCYN‐A1 (small cells) were higher than for UCYN‐A2/3/4 (large cells), consistent with the general size dependence of phytoplankton growth and grazing mortality. We found that Fe : DIN is a major determinant of UCYN‐A abundances in high‐latitude waters, where UCYN‐A could make substantial contributions to plankton food‐web cycling. [ABSTRACT FROM AUTHOR]

Background: Molecular identification of a wide range of organisms capable of carrying out biological nitrogen fixation (BNF) are diverse in nature and significantly improves plant growth. Biological N2 fixation reflects the activity of a phylogenetically diverse list of microorganisms. Molecular characterization provides efficient means to identify organisms with the potential of N2 fixation. Applying these techniques in an array of environments has considerably broadened our understanding of the suite of organisms that can carry out BNF. Methods: Thirty-four strains of free living N2 fixing bacterial strains were isolated from diverse plants cultivated in North Gujarat, including wheat, cotton, castor and pearl millet, using a nitrogen-free selective medium. Acetylene reduction assay was used to check the ability of all bacteria to fix nitrogen. Hybridization with nifH probe derived from Azotobacter vinelandii with isolated freeliving nitrogen-fixing bacteria showed a positive result. The selected strains were characterized by molecular analysis like; ARDRA and 16S rDNA sequencing. Result: Based on molecular characterization 17 strains to known groups of nitrogen-fixing bacteria, including organisms from the genus Azotobacter, Pseudomonas, Enterobacter, Arthrobacter, Bacillus, Variovorax, Nocardiodies, Rhodococcus, Mycobacterium, Planococcus, Microbacterium have been identified. One of the strains was identified as unknown bacteria. The potential strains were identified by 16 srDNA analysis and also corroborated by morphological and biochemical characterization. [ABSTRACT FROM AUTHOR]

【Objective】The study aimed to evaluate and identify the agronomic traits and nitrogen-fixing ability of Saccharum spontaneum L. germplasm resources, and to screen out special germplasm resources of nitrogen-fixing and acid-tolerant characteristics, so as to provide reference for innovation and breeding of S. spontaneum L. germplasm resources in China.【Method】Taking 33 samples of S. spontaneum L. as test materials, correlation analysis, cluster analysis, genome cloning and other methods were used to determine and analyze the plant height, stalk number, brix, dry matter rate and nitrogenase activity. Their endophytic nitrogen-fixing bacteria nifH gene was cloned to analyze its nitrogenase activity, root weight and root activity under acid stress, etc. Nitrogen-fixing S. spontaneum L. material with excellent comprehensive traits was screened and nitrogen-fixing and acid-tolerant S. spontaneum L. germplasms were identified.【Result】Genetic diversity of S. spontaneum L. germplasm was high. The average coefficients of variation of plant height, stalks number, brix, dry matter rate and nitrogenase activity were 31.73%,37.22%,40.69%,6.77% and 59.22%,respectively. Nitrogenase activity had the largest variation, indicating that some of the S. spontaneum L. germplasms varied greatly in nitrogen-fixing ability. The results of correlation analysis showed that there was a significant positive correlation between dry matter rate and brix, nitrogenase activity and stalk number（P<0.05,the same as below） and dry matter rate and stalk number were negatively correlated. Cluster analysis showed that the 33 samples of S. spontaneum L. could be divided into 4 groups at the Euclidean distance of 8.51,and the clustering results were consistent with the characteristics of the germplasm itself. Among them, 6 samples of S. spontaneum L. in the fourth group were of strongly high nitrogen-fixing multiple stalks, and 4 samples of S. spontaneum L. germplasms in the third group all had the characteristics of short and low dry matter rate. S. spontaneum L. could not be clearly clustered according to the geographical origin, but the germplasms with many similar traits could be clustered together, indicating that the phenotype and nitrogen-fixing ability of the germplasms of these S. spontaneum L. had changed significantly during the long-term evolution and natural selection. A large number of nitrogen-fixing bacteria with nitrogen-fixing gene nifH were cloned in germplasm GSM177 and GSM03,which further confirmed that GSM177 and GSM03 had nitrogen fixation ability. The results of acid resistance screening showed that the tolerance of GSM177 and GSM03 to acid soil was significantly different: GSM177 was more tolerant to acidity, while GSM03 was a typical acid-sensitive germplasm.【Conclusion】GSM177 has excellent performance for both nitrogen fixation and acid tolerance, which is valuable for genetic improvement for the two traits. [ABSTRACT FROM AUTHOR]

Since Inceptisols, in general, contain low soil organic matter and major plant nutrients, inorganic fertilizers are commonly added during corn cultivation. In order to maintain long-term soil health and fertility, bioferilizer and organic ameliorant application are suggested. The addition of nitrogen (N)-fixing bacteria (NFB) can benefit plant growth through the supply of available nitrogen for plant uptake. Organic ameliorants can enhance soil chemical and biological properties. A field trial had been performed to observe the effect of biofertilizer and organic ameliorant on corn growth, N status in soil and plant, and the yield and wasteof corn. The experiment was designed in a Completely Randomized Block Design that consisted of four treatments and six replications. The treatments were 1.2 kg/ha N-fixing mixed biofertilizer, 2 t/ha organic ameliorant, and mixtures of biofertilizer and ameliorant. Control plants received neither biofertilizer nor ameliorant. The experiment results found that N-fixing biofertilizer and ameliorant increased plant height, fully-developed leaves number, soil reaction and N uptake of corn compared to the control. The total-N content was slightly increased after NFB inoculation with and without amelioration over other treatments. Plots treated with biofertilizer and ameliorant produced a higher grain weight compared to the control treatment. Corn wastes such as empty corn cob and husk weight were increased in plants treated with biofertilizer, ameliorant and a combination of both. This study suggested that the combined application of biofertilizer and ameliorant produced 66% more grain yield and 84 % more cob and husk waste compared to untreated plants.

Although the anaerobic reduction of azo dyes is ecofriendly, high ammonia consumption remains a significant challenge. This work enriched a mixed nitrogen-fixing bacteria consortium (NFBC) using n-Fe 3 O 4 to promote the anaerobic reduction of methyl orange (MO) without exogenous nitrogen. The enriched NFBC was dominated by Klebsiella (80.77 %) and Clostridium (17.16 %), and achieved a 92.7 % reduction of MO with an initial concentration of 25 mg·L−1. Compared with the control, the consortium increased the reduction efficiency of MO, cytochrome c content, and electron transport system (ETS) activity by 11.86 %, 89.86 %, and 58.49 %, respectively. When using 2.5 g·L−1 n-Fe 3 O 4 , the extracellular polymeric substances (EPS) of NFBC were present in a concentration of 85.35 mg·g−1. The specific reduction rates of MO by NFBC were 2.26 and 3.30 times faster than those of Fe(II) and Fe(III), respectively, while the enrichment factor of the ribosome pathway in NFBC exceeded 0.75. Transcriptome, carbon consumption, and EPS analyses suggested that n-Fe 3 O 4 stimulated carbon metabolism and secreted protein synthesized by the mixed culture. The latter occurred due to the increased activity of consortium and the content of redox substances. These findings demonstrate that n-Fe 3 O 4 promoted the efficiency of mixed nitrogen-fixing bacteria for removing azo dyes from wastewater. This innovative approach highlights the potential of integrating nanomaterials with biological systems to effectively address complex pollution challenges. [Display omitted] • N 2 gas was the only source of N needed for the bioreduction of methyl orange. • The enriched consortium XL1, dominated by Klebsiella and Clostridium had a high reduction rate for methyl orange. • n-Fe 3 O 4 accelerated the release of redox-active substances by the mixed nitrogen-fixing bacteria. [ABSTRACT FROM AUTHOR]

Biological nitrogen fixation is a major important source of nitrogen for low-nutrient surface oceanic waters. Nitrogen-fixing (diazotrophic) cyanobacteria are believed to be the primary contributors to this process, but the contribution of non-cyanobacterial diazotrophic organisms in oxygenated surface water, while hypothesized to be important, has yet to be demonstrated. In this study, we used simultaneous 15N-dinitrogen and 13C-bicarbonate incubations combined with nanoscale secondary ion mass spectrometry analysis to screen tens of thousands of mostly particle-associated, cell-like regions of interest collected from the North Pacific Subtropical Gyre. These dual isotope incubations allow us to distinguish between non-cyanobacterial and cyanobacterial nitrogen-fixing microorganisms and to measure putative cell-specific nitrogen fixation rates. With this approach, we detect nitrogen fixation by putative non-cyanobacterial diazotrophs in the oxygenated surface ocean, which are associated with organic-rich particles (<210 µm size fraction) at two out of seven locations sampled. When present, up to 4.1% of the analyzed particles contain at least one active putative non-cyanobacterial diazotroph. The putative non-cyanobacterial diazotroph nitrogen fixation rates (0.76 ± 1.60 fmol N cell−1 d−1) suggest that these organisms are capable of fixing dinitrogen in oxygenated surface water, at least when attached to particles, and may contribute to oceanic nitrogen fixation. Nitrogen-fixing (diazotrophic) cyanobacteria provide a critical nutrient input to the ocean. Non-cyanobacterial diazotrophs are also thought to contribute, but they have not been observed to fix nitrogen. Using dual isotope labeling combined with nanoscale secondary ion mass spectrometry, this study demonstrates that putative non-cyanobacterial diazotrophs attached to particles can fix nitrogen. [ABSTRACT FROM AUTHOR]

Island biogeography has classically focused on abiotic drivers of species distributions. However, recent work has highlighted the importance of mutualistic biotic interactions in structuring island floras. The limited occurrence of specialist pollinators and mycorrhizal fungi have been found to restrict plant colonization on oceanic islands. Another important mutualistic association occurs between nearly 15,000 plant species and nitrogen-fixing (N-fixing) bacteria. Here, we look for evidence that N-fixing bacteria limit establishment of plants that associate with them. Globally, we find that plants associating with N-fixing bacteria are disproportionately underrepresented on islands, with a 22% decline. Further, the probability of N-fixing plants occurring on islands decreases with island isolation and, where present, the proportion of N-fixing plant species decreases with distance for large, but not small islands. These findings suggest that N-fixing bacteria serve as a filter to plant establishment on islands, altering global plant biogeography, with implications for ecosystem development and introduction risks. Plants associated with nitrogen-fixing bacterial symbionts are disproportionately underrepresented on islands, suggesting that these bacteria might play a limiting role in island plant biogeography. [ABSTRACT FROM AUTHOR]

Copyright of Revista Mexicana de Ciencias Agrícolas is the property of Instituto Nacional de Investigaciones Forestales, Agricolas y Pecuarias 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.)

Endophytic nitrogen-fixing bacteria are versatile and widely distributed in plants. Numerous strains of endophytic nitrogen-fixing bacteria are used as biofertilizers to minimize the utilization of chemical fertilizers, improve nutrient use efficiency, increase crop productivity, and reduce environmental pollution. However, the mechanism underlying the interaction between nitrogen-fixing bacteria and plants is still unclear. So, the present study was planned to assess the effects of endophytic nitrogenfixing bacteria on sugarcane by analyzing the changes in physiological and biochemical activities. In the current study, Klebsiella variicola DX120E, an endophytic nitrogen-fixing bacterium, was inoculated on sugarcane varieties B8 and ROC22 to evaluate the effects on nitrogen and carbon metabolism-related enzymatic activity and biomass. Results showed that DX120E inoculation improved the enzymatic activities related to gluconeogenesis and nitrogen metabolism increased the sugarcane plant's height, cane juice Brix, biomass, chlorophyll, and soluble sugar content in sugarcane. Metabolomics analysis revealed that the metabolome modules were highly enriched in carbon and nitrogen metabolic pathways of strain-affected sugarcane than uninoculated control. The identified carbohydrates were associated with the glycolysis or gluconeogenesis and tricarboxylic acid (TCA) cycle in plants. Metabolomic profiling in the present investigation showed that carbohydrate metabolism is coordinated with nitrogen metabolism to provide carbon skeletons and energy to amino acid synthesis, and amino acid degradation results in several metabolites used by the citric acid cycle as an energy source. Moreover, differentially expressed metabolites of non-proteinogenic amino acids have a further complementary role to the action of endophytic nitrogen-fixing bacteria. Meanwhile, a significant difference in metabolites and metabolic pathways present in stems and leaves of B8 and ROC22 varieties was found. This study discovered the potential benefits of DX120E in sugarcane and suggested candidate regulatory elements to enhance interactions between nitrogenfixing microbes and sugarcane. [ABSTRACT FROM AUTHOR]

The Sundarbans mangrove is a transitional zone between terrestrial land and sea, a unique location in our global geography. This study identifies the richness and population dynamics of bacterial populations along different seasons in the rooted and unrooted regions of soil sediments in Sundarbans, West Bengal. Throughout the year, bacterial populations were higher in the rooted sediment zone, than the unrooted area. The rooted zone contains more silt and clay but the unrooted zone harbours more silty, sandy soil. Salinity is lower in the unrooted zone. The heterotrophic bacterial populations were higher than other types of bacteria in both regions irrespective of seasonal variation. The results revealed that the most varied seasons were the monsoon season in the rooted and unrooted sediment region. The changes identified in this study were most likely due to variances in the microhabitat associated with mangrove root, physicochemical parameters and seasonal fluctuations. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Irrigation & Drainage is the property of Journal of Irrigation & Drainage 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.)

Many plants associate with arbuscular mycorrhizal fungi for nutrient acquisition, while legumes also associate with nitrogen-fixing rhizobial bacteria. Both associations rely on symbiosis signaling and here we show that cereals can perceive lipochitooligosaccharides (LCOs) for activation of symbiosis signaling, surprisingly including Nod factors produced by nitrogen-fixing bacteria. However, legumes show stringent perception of specifically decorated LCOs, that is absent in cereals. LCO perception in plants is activated by nutrient starvation, through transcriptional regulation of Nodulation Signaling Pathway (NSP)1 and NSP2. These transcription factors induce expression of an LCO receptor and act through the control of strigolactone biosynthesis and the karrikin-like receptor DWARF14-LIKE. We conclude that LCO production and perception is coordinately regulated by nutrient starvation to promote engagement with mycorrhizal fungi. Our work has implications for the use of both mycorrhizal and rhizobial associations for sustainable productivity in cereals. Lipochitooligosaccharide (LCO) perception by legumes is required to establish symbiotic relationships with nitrogen fixing bacteria. Here the authors show that nutrient starvation can activate LCO perception in cereals to promote symbiotic association with arbuscular mycorrhizal fungi. [ABSTRACT FROM AUTHOR]

Dioecious plant species have a high genetic variation that is important for coping with or adapting to environmental stress through natural selection. Intensive studies have reported dimorphism morphism in morphology, physiology, as well as biotic and abiotic stress responses in dioecious plants. Here, we demonstrated the dimorphism of metabolic profile and the preference of some microorganisms in the roots and rhizosphere soils of male and female papaya. The metabolic composition of roots were significantly different between the males and females. Some sex hormones occurred in the differential metabolites in roots and rhizosphere soils. For example, testosterone was up-regulated in male papaya roots and rhizosphere soils, whereas norgestrel was up-regulated in the female papaya roots, indicating a possible balance in papaya roots to control the sexual differentiation. Plant hormones such as BRs, JAs, SA and GAs were also detected among the differential metabolites in the roots and rhizosphere soils of dioecious papaya. In addition, some metabolites that have medicinal values, such as ecliptasaponin A, crocin, berberine and sapindoside A were also expressed differentially between the two sexes. Numerous differential metabolites from the papaya roots were secreted in the soil, resulting in the differences in microbial community structure in the roots and rhizosphere soils. Some nitrogen-fixing bacteria such as Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium, Brevundimonas and Microvirga were enriched in the male papaya roots or rhizosphere soils. While Candidatus Solibacter and Tumebacillus, which utilize organic matters, were enriched in the roots or rhizosphere soils of the female papaya. Some differences in the fungi abundance were also observed in both male and female papaya roots. These findings uncovered the effect of sex types on the metabolic and microbiota differences in roots and rhizosphere soils in papaya and will lead to investigations of underlining genomic and molecular mechanisms. [ABSTRACT FROM AUTHOR]

Background: Straw return may affect the soil nitrogen (N) balance by changing soil carbon (C) and N components and contents. To understand how straw return affects the soil N fixation capacity, the relationship between biological N fixation and changes in soil C and N contents at different depths need to be examined. Methods: Soil samples were collected at 20-cm intervals from 0 to 100 cm after five years of a rice-rape rotation system with straw return (ST) and without (CK). Organic C and inorganic N contents, potential N fixation rate, and abundance and population composition of N-fixing bacteria were analyzed at different soil depths. Results: Compared with CK, ST increased soil organic C (SOC), particulate organic C (POC), mineral-associated organic C (MOC), and total N (TN) but decreased nitrate–N (NO3−-N). Straw return also increased the abundance of N-fixing bacteria from 2.9- to 18-fold at depths from 0 to 40 cm and increased the potential N fixation rate at 0–20 cm by 25%. The annual biological N fixation rates at 0–60 cm by soil N-fixing bacteria were estimated to be approximately 0.13–2.70 and 0.12–2.16 kg·ha−1 in ST and CK, respectively. Long-term ST significantly affected the composition of N-fixing bacteria at depths from 0 to 40 cm. Conclusions: Long-term straw return can increase the abundance of the N-fixing bacteria and effectively alter the structure of the N-fixing bacterial community. SOC, POC, TN, and NO3−-N were the main environmental factors driving changes in abundance, activity, and population composition of soil N-fixing bacteria under ST. [ABSTRACT FROM AUTHOR]

Root endophytes are considered to be one of the potent environment-friendly substitutes for chemical fertilizers, as they possess an ability to induce crosstalk inside the hosts for growth promotion, nitrogen fixation, phosphate solubilization and iron sequestration. This study aimed to explore and evaluate the key root endophytic bacterial consortia of two widely cultivated varieties of rice (Oryza sativa L.), cv. 'Saraswati' (OS01) and cv. 'Kunti' (OS04). Detailed comparative metagenome data were generated for endophytes of OS01 and OS04 and the species richness was calculated. OS01 showed higher endophyte species richness than OS04, with alpha diversity values of 3.10 and 2.40, respectively. Bacillus, Magnetospirillum, Methanocystis, Desulfomicrobium and Pantoea were identified as common endophyte members for both cultivars. Solibacillus, Paenibacillus, Candidatus, and Melospira were unique members of OS01, and Herbaspirillum, Pandoraea, Anabaenopsis for OS04. Considerable occurrence of nitrogen fixing bacteria and methanogenic bacteria in the cultivars confirmed biological nitrogen fixation, which can contribute to plant development. Core homeotic pathways of amino acid biosynthesis and carbon metabolism were also reflected in endophytes from both cultivars, indicating a supportive environment for microorganisms. Sulfur metabolism pathways were likewise predicted to be active in the niche under study, which may be attributed as a response to arsenic stress. Furthermore, the most abundant genera identified may potentially serve as crucial consortium candidates for host plant development and contribute to better yield in a sustainable manner. [ABSTRACT FROM AUTHOR]

As the number of people on earth increases, so does the need for food. Providing the population with environmentally friendly agricultural food is one of the urgent problems of our time. Currently, the main direction of modern organic farming is the use of biofertilizers. Bacterial preparations are capable of influencing the physiological processes of plants in small quantities, leading to increase in plant productivity. The objective of this work was to study rhizobacteria associated with wheat roots. For this purpose, we took more than 100 isolates of rhizobacteria from the rhizosphere and root surface of wheat plants grown in irrigated fields of Tashkent, Syrdarya, Andijan, Kashkadarya regions. Rhizobacteria were grown on nutrient media of Döbereiner, Ashby, Pikovsky, and Zack, and 25 isolates of associative rhizobacteria were selected based on the characteristics of absorption of molecular nitrogen, mobilization of phosphorus and potassium. They actively dissolved Сa3(PO4)2 and KAlSiO4 for 3 days. They were found to produce organic acids. In organic farming, nitrogen-fixing, phosphorus- and potassium-mobilizing rhizobacteria are of great practical importance, while our experiments on obtaining biological products are considered as an environmentally friendly and cost-effective way to increase crop yields. From the surface of wheat roots grown in different zones of Uzbekistan, when screening for nitrogen fixation, we selected 3 isolates with acetylene reductase activity of 79–91 nmol C2H4/flacon/24h. We determined that bacteria completely mobilized phosphate, forming 100% acid when grown in a medium containing Ca3(PO4)2 for 5 days. The ability of the bacteria to mobilize potassium was studied on a nutrient KAlSiO4-containing medium. The bacteria were observed to mobilize potassium, forming 90–100% acid within 15 days. Based on the study of the 16S rRNA gene of bacteria, we identified rhizobacteria UT3, UT4, and UT9 as Rahnella aquatilis. [ABSTRACT FROM AUTHOR]

Considering the fact that the world's population shows an upward trajectory from one year to another, the need to ensure security at the global level by supplementing the production of agricultural crops has become a primary objective. Thus, in order to ensure the intake of proteins necessary for human consumption but also to meet the needs of the large paint-producing industries as well as livestock farms, soybean culture represents the conventional option for this demand, which is why in recent years this plant has become one of the most cultivated worldwide, due to the multiple properties it possesses, such as: symbiotic fixation of atmospheric nitrogen, it is an oleaginous plant and the protein content of the seeds is very high. Therefore, due to the desire to achieve quantitatively higher yields, the amount of chemical fertilizers applied either on the soil or incorporated at the time of sowing has increased, this causes soil pollution over time, which is why the decision was made to carry out this retrospective study in order to highlight in what proportions the distribution of chemical fertilizers influences the symbiotic fixation of atmospheric nitrogen by means of nitrogen-fixing bacteria and how it is possible that by cultivating this plant we can provide the preceding crop with the necessary amount of Nitrogen without carry out an additional application of chemical fertilizers, thus ensuring a healthier and more profitable crop but also a less polluted soil. [ABSTRACT FROM AUTHOR]

Understanding how Nature accomplishes the reduction of inert nitrogen gas to form metabolically tractable ammonia at ambient temperature and pressure has challenged scientists for more than a century. Such an understanding is a key aspect toward accomplishing the transfer of the genetic determinants of biological nitrogen fixation to crop plants as well as for the development of improved synthetic catalysts based on the biological mechanism. Over the past 30 years, the free-living nitrogen-fixing bacterium Azotobacter vinelandii emerged as a preferred model organism for mechanistic, structural, genetic, and physiological studies aimed at understanding biological nitrogen fixation. This review provides a contemporary overview of these studies and places them within the context of their historical development. [ABSTRACT FROM AUTHOR]

Drought stress is one of the most fatal environmental phenomena that affect plant growth and productivity worldwide. In the present study, an attempt was made to screen and characterize nitrogen fixing bacteria for drought tolerance by inoculation in trypticase soy broth with different concentrations of PEG 6000. The strains were further evaluated for induction of drought tolerance and growth promotion in tomato. It was found that inoculation improved the plant physiological parameters of tomato seedlings. Furthermore, plants inoculated with nitrogen fixers viz., Microbacterium, Cellulosimicrobium and Paenibacillus showed better growth in terms of plant height, number of leaves, stem girth, root length, fresh and dry weight of plants and yield compared to uninoculated control plants under normal and reduced irrigation. The study demonstrates nitrogen fixers with plant growth promoting traits and drought tolerance can be a useful approach for the development of bioinoculants for drought stress management in crops. [ABSTRACT FROM AUTHOR]