Nitrogen-fixing Soil Bacteria Research Articles

Enacting partner specificity in legume–rhizobia symbioses

AbstractLegumes, such as peas, beans, and alfalfa, have evolved a remarkable ability to establish root nodule symbioses with nitrogen-fixing soil bacteria to fulfill their nitrogen needs. This partnership is characterized by a high degree of specificity, occurring both within and between host and bacterial species. Consequently, nodulation capacity and nitrogen-fixing efficiency vary significantly among different plant–bacteria pairs. The genetic and molecular mechanisms regulating symbiotic specificity are diverse, involving a wide array of host and bacterial genes and signals with various modes of action. Understanding the genetic basis of symbiotic specificity could enable the development of strategies to enhance nodulation capacity and nitrogen fixation efficiency. This knowledge will also help overcome the host range barrier, which is a critical step toward extending root nodule symbiosis to non-leguminous plants. In this review, we provide an update on our current understanding of the genetics and evolution of recognition specificity in root nodule symbioses, providing more comprehensive insights into the molecular signaling in plant–bacterial interactions.

Nitrogen Addition Increased the Greenhouse Gas Emissions of Permafrost Peatland Due to the Abundance of Soil Microbial Functional Genes Increasing in the Great Khingan Mountains, Northeast China

Permafrost peatlands are sensitive to changes in nitrogen levels because they are largely nitrogen-limited ecosystems. However, the microbial mechanisms by which the addition of nitrogen increases the emission of greenhouse gasses from permafrost peatlands remain unclear. This study was conducted to decipher the relationship between greenhouse gas emissions and soil microorganisms under nitrogen addition. Here, we performed a 154-day experimental investigation in order to assess the release of greenhouse gasses such as CO2, CH4, and N2O from the soils. Additionally, we examined the correlation between the rates of these gas emissions and the presence of crucial microbial functional genes in the soil. The results showed that the addition of low (0.01 g kg−1), medium (0.02 g kg−1), and high (0.04 g kg−1) levels of nitrogen increased the cumulative CO2 emissions by 2.35%–90.42%, respectively. The cumulative emissions of CH4 increased by 17.29%, 25.55% and 21.77%, respectively. The cumulative emissions of N2O increased 2.97, 7.49 and 7.72-fold. The addition of nitrogen increased the abundance of functional genes in the bacteria, fungi, methanogens, denitrifying bacteria, and nitrogen-fixing bacteria in soil by modifying abiotic soil variables and providing sufficient substrates for microorganisms. The results indicated that the addition of nitrogen can significantly promote the emission of greenhouse gasses by increasing the abundance of functional microbial genes in the soil of permafrost peatlands. These findings highlight the importance of considering nitrogen deposition and the nitrogen released from thawing permafrost when predicting the future greenhouse gasses emitted from permafrost peatlands.

Influence of Bacterial Fertilizers on the Structure of the Rhizospheric Fungal Community of Cereals South of Western Siberia

The general lack of knowledge on the conditions of Western Siberia (Omsk region) and the taxonomic diversity of zonal soils determines the relevance of these studies. The research was carried out in order to study the effect of complex biologics on the taxonomic diversity of the fungal component of the microbiome of the rhizosphere of cereals and the phytosanitary condition of crops in the southern forest-steppe (meadow-chernozem soil) and subtaiga (gray forest soil) zones of the Omsk Irtysh region (Western Siberia). This work was carried out in 2022–2023, using laboratory studies in combination with field experiments and metagenomic and statistical analyses. The objects of research were varieties of cereals and grain forage crops of Omsk selection: soil microorganisms. The scheme of the experiment involved the study of the following options: varieties of cereals (factor A): spring soft wheat—Omsk 42, Omsk 44, Tarskaya 12; durum wheat—Omsk coral; barley—Omsk 101; oats—Siberian hercules; bacterial preparation for seed inoculation (factor B) without the drug—Mizorin and Flavobacterin. The sampling of the plant rhizosphere for metagenomic analysis was carried out during the earing phase (July). For the first time, the taxonomic composition of the fungal community was determined based on the analysis of amplicon libraries of fragments of ribosomal operons of ITS2 fungi during colonization of crop roots by nitrogen-fixing bacteria in various soil and climatic zones of the Omsk region. The fungal component of the microbiome was analyzed in two zones of the Omsk region (southern forest-steppe and subtaiga). The five dominant phyla of soil fungi were located in the following decreasing series: Ascomycota (about 70%) > Mortierellomycota (about 7%) > Basidiomycota (about 5%) > Mucoromycota (3%) > Chytridiomycota (1%). The five main genera of fungi inhabiting the rhizosphere of cereals are located in a decreasing row: Giberella (6.9%) > Mortierella (6.6%) > Chaetomium (4.8%) > Cladosporium (3.8%) > Rhizopus (3.3%). The predominantly positive effect of biologics of associative nitrogen fixation on the fungal community of the soil (rhizosphere) of experimental sites located in different soil and climatic zones has been established. During seed bacterization, the growth of saprotrophic fungal genera was noted in relation to the control variants Pseudogymnoascus, Chloridium, Clonostachys, Trihoderma, etc., and the fungicidal properties of bacterial strains introduced into the soil were actively manifested relative to phytopathogenic fungi of the genera Alternaria, Blumeria, Fusarium, etc. According to the results of determining the number of infectious structures of Rhizoctonia solani, it was found that the population of the soil with viable cells of this pathogen was 1–3 pcs/g (below the threshold of harmfulness, PV 20 pcs/g of soil), which indicates a favorable phytosanitary situation with respect to the pathogen. The fungicidal effect of the applied bacterial fertilizers on Rhizoctonia solani could not be detected. The number of Bipolaris sorokiniana varied depending on the drug used. In the conditions of the southern forest-steppe zone of the Omsk region (meadow-chernozem soil), the greatest fungicidal effect was noted in Flavobacterin application variants on wheat of the Omsk 42 variety, durum wheat of the Omsk coral variety, and barley; the decrease in conidia relative to the control was 73, 35, and 29%, respectively. In the subtaiga zone of the Omsk Irtysh region (gray forest soil), as in the southern forest-steppe zone, pre-sowing bacterization of seeds with Flavobacterin led to a decrease in Bipolaris sorokiniana in the rhizosphere of wheat of the Omsk 42 variety by 18%, and oats by 27%, to control. The use of the drug Mizorin in some variants of the experiment led to an insignificant decrease in the harmful fungus or had no effect at all.

Spatial distribution of nitrogen content and nitrogen fixing bacteria in soil of Damietta Governorate centers

Spatial distribution of nitrogen content and nitrogen fixing bacteria in soil of Damietta Governorate centers

Epigenetic control during root development and symbiosis.

The roots of plants play multiple functions that are essential for growth and development, including anchoring to the soil as well as water and nutrient acquisition. These underground organs exhibit the plasticity to modify their root system architecture in response to environmental cues, allowing adaptation to change in water and nutrient availability. In addition, roots enter in mutualistic interactions with soil microorganisms, for example, the root nodule symbiosis (RNS) established between a limited group of plants and nitrogen-fixing soil bacteria and the arbuscular mycorrhiza symbiosis involving most land plants and fungi of the Glomeromycetes phylum. In the past 20 years, genetic approaches allowed the identification and functional characterization of genes required for the specific programs of root development, root nodule, and arbuscular mycorrhiza symbioses. These genetic studies provided evidence that the program of the RNS recruited components of the arbuscular mycorrhiza symbiosis and the root developmental programs. The execution of these programs is strongly influenced by epigenetic changes-DNA methylation and histone post-translational modifications-that alter chromatin conformation modifying the expression of key genes. In this review, we summarize recent advances that highlight how DNA methylation and histone post-translational modifications, as well as chromatin remodeling factors and long noncoding RNAs, shape the root system architecture and allow the successful establishment of both root nodule and arbuscular mycorrhiza symbioses. We anticipate that the analysis of dynamic epigenetic changes and chromatin 3D structure in specific single cells or tissue types of root organs will illuminate our understanding of how root developmental and symbiotic programs are orchestrated, opening exciting questions and new perspectives to modulate agronomical and ecological traits linked to nutrient acquisition.

Identification and Characterization of a Bacterial Periplasmic Solute Binding Protein That Binds l-Amino Acid Amides.

Periplasmic solute-binding proteins (SBPs) are key ligand recognition components of bacterial ATP-binding cassette (ABC) transporters that allow bacteria to import nutrients and metabolic precursors from the environment. Periplasmic SBPs comprise a large and diverse family of proteins, of which only a small number have been empirically characterized. In this work, we identify a set of 610 unique uncharacterized proteins within the SBP_bac_5 family that are found in conserved operons comprising genes encoding (i) ABC transport systems and (ii) putative amidases from the FmdA_AmdA family. From these uncharacterized SBP_bac_5 proteins, we characterize a representative periplasmic SBP from Mesorhizobium sp. A09 (MeAmi_SBP) and show that MeAmi_SBP binds l-amino acid amides but not the corresponding l-amino acids. An X-ray crystal structure of MeAmi_SBP bound to l-serinamide highlights the residues that impart distinct specificity for l-amino acid amides and reveals a structural Ca2+ binding site within one of the lobes of the protein. We show that the residues involved in ligand and Ca2+ binding are conserved among the 610 SBPs from experimentally uncharacterized FmdA_AmdA amidase-associated ABC transporter systems, suggesting these homologous systems are also likely to be involved in the sensing, uptake, and metabolism of l-amino acid amides across many Gram-negative nitrogen-fixing soil bacteria. We propose that MeAmi_SBP is involved in the uptake of such solutes to supplement pathways such as the citric acid cycle and the glutamine synthetase-glutamate synthase pathway. This work expands our currently limited understanding of microbial interactions with l-amino acid amides and bacterial nitrogen utilization.

Effects of root-applied biochar on soil nitrogen transformation and root nitrogen metabolism of cucumber seedlings in facility continuous cropping soils.

The problem of soil barrier caused by excessive accumulation of nitrogen is common in continuous cropping soil of facility agriculture. To investigate the modulating effects of biochar amendment on soil nitrogen transformation in greenhouse continuous cropping systems, we conducted a pot experiment with two treatments, no biochar addition (CK) and 5% biochar addition (mass ratio). We analyzed the effects of biochar addition on soil microbial community structure, abundances of genes functioning in nitrogen cycling, root growth and nitrogen metabolism-related genes expressions of cucumber seedlings. The results showed that biochar addition significantly increased plant height, root dry mass, total root length, root surface area, and root volume of cucumber seedlings. Rhizosphere environment was improved, which enhanced root nitrogen absorption by inducing the up-regulation of genes expressions related to plant nitrogen metabolism. Biochar addition significantly increased soil microbial biomass nitrogen, nitrate nitrogen, and nitrite nitrogen contents. The abundances of bacteria that involved in nitrogen metabolism, including Proteobacteria, Cyanobacteria, and Rhizobiales (soil nitrogen-fixing bacteria), were also significantly improved in the soil. The abundances of genes functioning in soil nitrification and nitrogen assimilation reduction, and the activities of enzymes involved in nitrogen metabolisms such as hydroxylamine dehydrogenase, nitronate monooxygenase, carbonic anhydrase were increased. In summary, biochar addition improved soil physicochemical properties and microbial community, and affected soil nitrogen cycling through promoting nitrification and nitrogen assimilation. Finally, nitrogen adsorption capacity and growth of cucumber plant was increased.

Effect of cover crop on soil fertility and bacterial diversity in a banana plantation in southwestern China

A cover crop can be an effective strategy to mitigate soil degradation in crops, such as banana. In this study, soil bacterial diversity, chemical properties, enzymatic activities, and bacterial nutrient-related functional genes were examined in the intercropping area of a banana plantation from 2018 to 2020 that had conventional tillage with bare soil (CT), natural weed cover (WC), which was primarily goosegrass (Eleusine indica (L.) Gaerth), or a cover crop of cultivated Siratro (Macroptilium atropurpureum (DC.) Urb.) (SC). By 2020, SC followed by WC and CT treatments were higher in soil organic matter, available nitrogen, total nitrogen and total phosphorus content as well as increased phosphatase, catalase, invertase and urease activities. Compared to CT and WC treatments, the co-occurrence network of SC treatment had higher modularity index indicating a more stable bacterial community. The composition of community was significantly different between the CT and SC treatments in 2019 and 2020, and the WC treatment in 2020. The relative abundance of fatty acids and lipid biosynthesis genes in the soil bacterial microbiome were significantly higher with SC compared to CT and WC in 2019 and 2020, as well as for carbon and nitrogen functional genes in 2020. However, the relative abundance of nucleoside and nucleoside biosynthesis genes were significantly lower with SC compared to CT and WC in 2020. SC treatment increased the relative abundance of Bradyrhizobium and MND1 related to nitrogen cycle and utilization compared to CT in 2019 and 2020. In general, the major benefits of a Siratro cover crop was increased soil organic matter, nitrogen content, and nitrogen fixing bacteria, as well as a more stable soil bacterial community, indicating that it provided multiple potential benefits to the soil of banana.

ВЛИЯНИЕ ЛЕКТИНА Paenibacillus polymyxa 1460 (ЛII) НА ЛИПИДНЫЙ СПЕКТР КРОВИ САМЦОВ КРЫС ПРИ АНТИБИОТИКО-АССОЦИИРОВАННОМ ДИСБАКТЕРИОЗЕ

Paenibacillus polymyxa 1460 lectin (LII) isolated from the surface of soil nitrogen-fixing bacteria were shown to, contributes to the optimization of lipid metabolism in the organism of male albino rats with antibiotic-associated dysbacteriosis leading to the normal are important biochemical parameters in blood such as total cholesterol (TC), high density lipoproteins (HDL-C), low density lipoprotein (TC-LDL), lipoprotein very low density (XC-VLDL). The study of the effect of Paenibacillus polymyxa 1460 (LII) lectin on animal metabolism is important for understanding the mechanisms underlying the metabolic activity of these substances, and reveals the possibilities of its application in the practice of biomedical research with the prospect of its use as biologically active substances.

Draft Genome Sequence of the Commercial Strain Rhizobium ruizarguesonis bv. viciae RCAM1022

Legume plants enter a symbiosis with soil nitrogen-fixing bacteria (rhizobia), thereby gaining access to assimilable atmospheric nitrogen. Since this symbiosis is important for agriculture, biofertilizers with effective strains of rhizobia are created for crop legumes to increase their yield and minimize the amounts of mineral fertilizers required. In this work, we sequenced and characterized the genome of Rhizobium ruizarguesonis bv. viciae strain RCAM1022, a component of the ‘Rhizotorfin’ biofertilizer produced in Russia and used for pea (Pisum sativum L.).

Metagenomic Profile of Endophytic Bacteria in Acacia mearnsii.

Acacia mearnsii is one of the invasive plants belonging to the Mimosaceae family. The family is known to be able to symbiosis with some endophytic nitrogen-fixing soil bacteria. Such ability will significantly contribute to plant growth and development by influencing nutrient uptake and stress tolerance and thus to improve soil conditions for a better and more fertile. Comprehensive identification of bacterial population dynamic in that zone should elucidate symbiosis mechanism that in turn can be used for soil improvement. Metagenomic-based profiling are now commonly used in studying whole total microbial communities in nature. Sampling of the root was collected from A. mearnsii young trees grown in Alahan Panjang at 60 and 120 days after transplanting, sterilized and stored at -80°C in a falcon tube before being subjected to metagenome analysis. The dynamics of growth and diversity of endophytic microbes were checked through amplicon sequence of the 16S rRNA gene in the V3-V4 region using Next Generation Sequencing (NGS) platform. Data analysis was performed using the QIIME2 application. The metagenomics analysis of endophytic bacteria on root A. mearnsii elucidates that the Proteobacteria is a dominant phyla in A. mearnsii root and analysis at the genera level shows that most of the Proteobacteria is dominated by the Bradyrhizobium which increase significantly during early growth phase.

EXPLORATION AND MORPHOLOGICAL CHARACTERIZATION OF PHOSPHATE-SOLUBILIZING AND NITROGEN-FIXING BACTERIA IN SALINE SOIL

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.

The common garden environment and genetic differentiation jointly influence the diversity and community structure of nitrogen-fixing bacteria in the rhizosphere soil of three <i>Caragana</i> species

The common garden environment and genetic differentiation jointly influence the diversity and community structure of nitrogen-fixing bacteria in the rhizosphere soil of three <i>Caragana</i> species

Diazotrophic bacterium Azotobacter vinelandii as a mutualistic growth promoter of an aquatic plant: Lemna minor

Lemnaceae plants, commonly referred to as duckweeds, are small planktonic terrestrial freshwater plants that live in symbiosis with various microbial communities. Azotobacter vinelandii are typical free-living nitrogen fixing soil bacteria that indirectly benefit plants by providing nitrogen compounds. In this study, Lemna minor RDSC 5512 and A. vinelandii ATCC 12837 = NBRC 13581 were co-cultured under gnotobiotic conditions. The growth of L. minor colonized by A. vinelandii was accelerated in both nitrogen-containing and nitrogen-free water conditions. The growth promotion effect is attributed to several plant growth promotion factors produced by the bacterium as well as biological nitrogen fixation in nitrogen-free condition. Moreover, L. minor elevated the nitrogen fixing activity of A. vinelandii and the cell number of A. vinelandii on L. minor increased continuously over 30 d. These observations indicated that L. minor provides a favorable environment for A. vinelandii colonization, allowing them to mutually benefit and flourish through syntrophism.

Engineered Nanoparticles, Natural Nanoclay and Biochar, as Carriers of Plant-Growth Promoting Bacteria.

The potential of biochar and nanoparticles to serve as effective delivery agents for beneficial bacteria to crops was investigated. Application of nanoparticles and biochar as carriers for beneficial bacteria improved not only the amount of nitrogen-fixing and phosphorus-solubilizing bacteria in soil, but also improved chlorophyll content (1.2-1.3 times), cell viability (1.1-1.5 times), and antioxidative properties (1.1-1.4 times) compared to control plants. Treatments also improved content of phosphorus (P) (1.1-1.6 times) and nitrogen (N) (1.1-1.4 times higher) in both tomato and watermelon plants. However, the effect of biochars and nanoparticles were species-specific. For example, chitosan-coated mesoporous silica nanoparticles with adsorbed bacteria increased the phosphorus content in tomato by 1.2 times compared to a 1.1-fold increase when nanoclay with adsorbed bacteria was applied. In watermelon, the situation was reversed: 1.1-fold increase in the case of chitosan-coated mesoporous silica nanoparticles and 1.2 times in case of nanoclay with adsorbed bacteria. Our findings demonstrate that use of nanoparticles and biochar as carriers for beneficial bacteria significantly improved plant growth and health. These findings are useful for design and synthesis of novel and sustainable biofertilizer formulations.

Provenance of rhizobial symbionts is similar for invasive and noninvasive acacias introduced to California.

Plant-soil interactions can be important drivers of biological invasions. In particular, the symbiotic relationship between legumes and nitrogen-fixing soil bacteria (i.e. rhizobia) may be influential in invasion success. Legumes, including Australian acacias, have been introduced into novel ranges around the world. Our goal was to examine the acacia-rhizobia symbiosis to determine whether cointroduction of non-native mutualists plays a role in invasiveness of introduced legumes. To determine whether acacias were introduced abroad concurrently with native symbionts, we selected four species introduced to California (two invasive and two noninvasive in the region) and identified rhizobial strains associating with each species in their native and novel ranges. We amplified three genes to examine phylogenetic placement (16S rRNA) and provenance (nifD and nodC) of rhizobia associating with acacias in California and Australia. We found that all Acacia species, regardless of invasive status, are associating with rhizobia of Australian origin in their introduced ranges, indicating that concurrent acacia-rhizobia introductions have occurred for all species tested. Our results suggest that cointroduction of rhizobial symbionts may be involved in the establishment of non-native acacias in their introduced ranges, but do not contribute to the differential invasiveness of Acacia species introduced abroad.

Impact assessment of cement industry activities on soil nitrogen-fixing bacteria

Impact assessment of cement industry activities on soil nitrogen-fixing bacteria

Small-volume additions of forest topsoil improve root symbiont colonization and seedling growth in mine reclamation

Beneficial soil microbes, such as mycorrhizal fungi and nitrogen-fixing bacteria, can improve plant nutrient acquisition and increase plant resilience to stressors. Yet, the waste materials left behind following major disturbances, such as mining, have negligible biological activity and fresh topsoil availability for reclamation is often limited. We tested if small-volume additions of native forest topsoil can improve early seedling survival and growth, and promote colonization of beneficial root symbionts. In a greenhouse experiment, we grew seedlings representing different functional groups in tailings and glacial-till overburden from the Mount Polley Mine, Canada. We applied 5 % (38 mL) and 25 % (188 mL) forest-soil additions for comparison with tailings/overburden controls and reference forest soil. The experiment was replicated with sterilized soil to isolate the biological effects of the forest soil from the physical and chemical effects. Willow (Salix scouleriana) and spruce (Picea engelmannii x glauca) seedling survival and growth increased with proportion of forest soil, which corresponded with increased ectomycorrhizal fungal colonization. Forest soil additions benefited seedlings grown in both overburden and tailings, with ~200 mL (25 %) forest soil additions generally supporting initial seedling growth comparable to seedlings grown in reference forest soil. Alder (Alnus viridis) showed minimal benefit from forest soil additions, likely due to a lack of nitrogen-fixing bacteria in the forest soil, highlighting the importance of matching the plant and microbial communities of the soil donor site with the target plant species. Differential results among plant species in sterilized soil indicated that plants exhibiting greater dependence on microbial symbionts (spruce and alder), benefited from the biological component of the inoculum, while willow, an early successional species with low mycorrhizal dependence, benefited from the physical and chemical properties of the forest soil. This research showed that targeted additions of small volumes of topsoil from native ecosystems can improve initial seedling survival and growth, and promote recovery of limiting soil microbial communities, making it a promising approach for mine reclamation when topsoil availability is limited.

Degradation reduces the diversity of nitrogen-fixing bacteria in the alpine wetland on the Qinghai-Tibet Plateau.

Biological nitrogen fixation is a key process in the nitrogen cycle and the main source of soil available nitrogen. The number and diversity of nitrogen-fixing bacteria directly reflect the efficiency of soil nitrogen fixation. The alpine wetland on the Qinghai-Tibet Plateau (QTP) is degrading increasingly, with a succession toward alpine meadows. Significant changes in soil physicochemical properties accompany this process. However, it is unclear how does the soil nitrogen-fixing bacteria change during the degradation processes, and what is the relationship between these changes and soil physicochemical properties. In this study, the nifH gene was used as a molecular marker to further investigate the diversity of nitrogen-fixing bacteria at different stages of degradation (none, light, and severe degeneration) in the alpine wetland. The results showed that wetland degradation significantly reduced the diversity, altered the community composition of nitrogen-fixing bacteria, decreased the relative abundance of Proteobacteria, and increased the relative abundance of Actinobacteria. In addition to the dominant phylum, the class, order, family, and genus of nitrogen-fixing bacteria had significant changes in relative abundance. Analysis of Mantel test showed that most soil factors (such as pH, soil water content (SWC), the organic carbon (TOC), total nitrogen (TN), and soil C:P ratio) and abundance had a significant positive correlation. TOC, TN, total phosphorus (TP), soil C:P ratio and Shannon had a significant positive correlation with each other. The RDA ranking further revealed that TOC, SWC, and TN were the main environmental factors influencing the community composition of nitrogen-fixing bacteria. It is found that the degradation of the alpine wetland inhibited the growth of nitrogen-fixing bacteria to a certain extent, leading to the decline of their nitrogen-fixing function.

Obtaining Osmo-resistant Mutants in Nitrogen-Fixing Bacteria Isolated from Saline Soils.

Annually, about, more than 7% of the Earth's land area becomes inappropriate for agriculture subsequently of salinization and desertification. Biofertilizers based on halophilic nitrogen-fixing bacteria can restore saline soils and stimulate plant growth, having a positive effect on germination, development of stems and roots, and fruiting. The aim of this work was to obtain osmo-resistant (Osm-r) nitrogen-fixing mutants isolated from saline soils of Armenia and selection of the best ones. To achieve this goal, we have obtained a collection of Osm-r strains based on soil nitrogen-fixing bacteria without the use of genetically modified technologies, which is an innovation in sphere of soil microbiology, and, especially, in nitrogen-fixing microorganisms. These mutants were obtained on the basis of Agrobacterium sp. Y-2 and Agrobacterium sp. M-1 nitrogen-fixing strains, both spontaneously and induced. Four strains with the higher nitrogen-fixing ability, which kept their vital activity in an environment with a high concentration of salts, were selected from collection of mutants. Selected strains in the future can become the basis for creating a new, effective, environmentally friendly biofertilizer for saline soils because they are plasmidless and have the highest priority for intensive use in agriculture.