Symbiotic Nitrogen-fixing Bacteria Research Articles

The Plant Growth-Promoting Ability of Alfalfa Rhizobial Strains Under Nickel Stress.

The growth and nutrient balance of legumes can be disrupted in soils with increased nickel (Ni) concentrations. The inoculation of legumes with rhizobia, symbiotic nitrogen-fixing bacteria, can be used for the alleviation of trace metal stress in plants. This study evaluated the Ni tolerance of alfalfa rhizobia isolates and some plant growth-promoting traits in the presence of Ni: indole-3-acetic acid (IAA) production, Ni biosorption potential, and the effect of rhizobia on alfalfa (Medicago sativa L.) growth. The strains were characterized as Shinorhizobium meliloti, Sinorhizobium medicae, and Rhizobium tibeticum. In total, 70% of the tested strains tolerate up to 0.8 mM Ni, while 15% of the strains tolerate 1.2 mM Ni. The production of IAA was maintained in the presence of Ni until bacterial growth was stopped by raising the Ni concentration. Alfalfa seed germination is significantly reduced in the presence of 0.5 mM Ni, while a significant reduction in 10-day-old seedling length already occurs at a Ni concentration of 0.03 mM. In the plant experiment, when alfalfa was inoculated with rhizobial strains, nodulation was maintained up to 0.05 mM Ni, but a significant reduction in nodule number was detected at 0.01 mM Ni. At the concentration of 0.005 mM Ni, inoculation with 12 particular rhizobial strains significantly improved the number of nodules per plant, plant height, and root length, as well as plant shoot dry weight, compared to non-inoculated plants with Ni addition. However, higher concentrations caused a reduction in all of these plant growth parameters compared to the plants without Ni. The selected rhizobia strains showed a Ni biosorption capacity of 20% in the in vitro assay. The inoculation of alfalfa with effective rhizobial strains improves growth parameters compared to non-inoculated plants in the presence of certain concentrations of Ni.

Backbone and side‑chain 1H, 13C and 15N resonance assignments and secondary structure determination of the rhizobial FixJ.

The symbiotic nitrogen-fixing bacterium Bradyrhizobium japonicum (B.japonicum) enables high soybean yields with little or no nitrogen fertiliser. A two component regulatory system comprising FixL, a histidine kinase with O2-sensing activity, and FixJ, a response regulator, controls the expression of genes involved in nitrogen fixation, such as fixK and nifA. Only under anaerobic conditions, the monophosphate group is transferred from FixL to the N-terminal receiver domain of FixJ (FixJN), which eventually promote the association of the C-terminal effector domain (FixJC) to the promoter regions of the nitrogen-fixation-related genes. Structural biological analyses carried out so far for rhizobial FixJ molecules have proposed a solution structure for FixJ that differs from the crystal structures, in which the two domains are extended. To understand the FixJ activation caused by phosphorylation of the N-terminal domain, which presumably regulates through the interactions between FixJN and FixJC, here we have performed backbone and sidechain resonance assignments of the unphosphorylated state of B. japonicum FixJ.

Effects of nitrogen-fixing bacteria on seabuckthorn growth (Hippophae rhamnoides. L)

Mongolia's fertilizer industry produces 2,000 tons of fertilizer in 10 years, while imports amount to 6-8 tons a year. One of the main biological features of the root system of sea buckthorn is the ability to absorb nitrogen from the air with the help of its root nodules. The main goal of the research is to identify the native nitrogen-absorbing bacteria of sea buckthorn and to increase their activity by preparing bacterial fertilizers and determining their effects on plants. In our study, we obtained 2 types of nitrogen-fixing bacteria using common microbiological methods. Sea buckthorn mongolica subspecies was used in this study. The study of root nodules of sea buckthorn (Hippophae rhamnoides L.) aims to identify symbiotic nitrogen-fixing bacteria. Sea buckthorn root nodules contain Frankia actinorrhizal microorganisms. Sea buckthorn seedlings, including those fertilized with nitrogen-fixing bacterial cultures, showed a positive correlation with plant growth. From June to September, when air temperatures are high and photosynthesis active in the field, the number of bacterial cells and nitrogenase activity were found to elevate in the root nodules of sea buckthorn plants. During this period, the roots extended 1.4 to 2.0 meters in length. The first- and second-order small roots, along with the main root, began forming small nodules filled with microorganisms. These microorganisms play a crucial role in capturing nitrogen in its molecular form from the air and converting it into a form usable by plants. However, studies on the diversity and distribution of Frankia strains have been hindered by challenges in isolating them from field-collected root nodules. In the field, nitrogenase activity in root nodules remained high from May to September, corresponding with the periods of high air temperatures and active photosynthesis.

A Comparison of Rice Root Microbial Dynamics in Organic and Conventional Paddy Fields.

The assembly of plant root microbiomes is a dynamic process. Understanding the roles of root-associated microbiomes in rice development requires dissecting their assembly throughout the rice life cycle under diverse environments and exploring correlations with soil properties and rice physiology. In this study, we performed amplicon sequencing targeting fungal ITS and the bacterial 16S rRNA gene to characterize and compare bacterial and fungal community dynamics of the rice root endosphere and soil in organic and conventional paddy fields. Our analysis revealed that root microbial diversity and composition was significantly influenced by agricultural practices and rice developmental stages (p < 0.05). The root microbiome in the organic paddy field showed greater temporal variability, with typical methane-oxidizing bacteria accumulating during the tillering stage and the amount of symbiotic nitrogen-fixing bacteria increasing dramatically at the early ripening stage. Redundancy analysis identified ammonium nitrogen, iron, and soil organic matter as key drivers of microbial composition. Furthermore, correlation analysis between developmental stage-enriched bacterial biomarkers in rice roots and leaf mineral nutrients showed that highly mobile macronutrient concentrations positively correlated with early-stage biomarkers and negatively correlated with later-stage biomarkers in both paddy fields. Notably, later-stage biomarkers in the conventional paddy field tended to show stronger correlations with low-mobility nutrients. These findings suggest potential strategies for optimizing microbiome management to enhance productivity and sustainability.

Isolation of Rhizobium from Moisture Stress Imposed Groundnut Nodules

Groundnut is an important oil seed crop accounts for a less than half of the major oilseeds produced in the country. Oil content of Groundnut varies from 44 % to 50 % depending upon the varieties and agronomic practices. It is also called as ‘king of oil seeds’ More than 85 % of the crop Is grown under rainfed conditions in low fertile soils. Rhizobium is a well-known symbiotic nitrogen fixing bacteria. Inoculation of Rhizobium improves plant growth, pod kernel and Oil yield. Rhizobium species help in improving root nodulation and nitrogen fixation, enhancing plant growth and yield of leguminous plants including groundnut under moisture stress conditions. Hence the present study is to isolate Rhizobium species from groundnut nodules by following method given by Vincent (1970) after growing them on Yeast Mannitol Agar Media morphological characteristics were studied, which can be further used for improving nodulation efficiency and plant growth promotion under moisture stress conditions.

Changes in the rhizosphere and root-associated bacteria community of white Guinea yam (Dioscorea rotundata Poir.) impacted by genotype and nitrogen fertilization

The bacterial diversity and composition of water yam (Dioscorea alata L. cv. A-19), which can grow without chemical fertilization, have recently been characterized with no significant differences compared with the use of chemical fertilization. However, the diversity and community structure of bacteria associated with the white Guinea yam (Dioscorea rotundata), the most cultivated and economically important yam in West Africa, have not yet been investigated. This study characterized the bacterial diversity and composition associated with bulk soil, rhizosphere, and plant roots in six white Guinea yam genotypes (S004, S020, S032, S042, S058, and S074) in field experiments in Ibadan, Nigeria under N-based chemical fertilizer application. The largest diversity of bacteria was found in the bulk soil, followed by the rhizosphere and roots. Based on the alpha diversity analysis, the bacterial diversity in both S020 and S042 increased with fertilizer application among the bulk soil samples. S058 grown under no-fertilizer conditions had the highest bacterial diversity among the rhizosphere samples. Beta diversity analysis highlighted the significant difference in the composition of bacteria associated with the genotypes and fertilizer treatments, and S032 had a unique bacterial composition compared to the other genotypes. The dominant phylum across all sample types was Proteobacteria. Actinobacteriota was the dominant phylum among bulk soil samples. At the genus level, Bacillus was the most abundant bacterial genus across both the control and treated samples. Pseudomonas was predominant across all rhizosphere samples. Chryseobacterium, Sphingobium, Delftia and Klebsiella associated with the rhizosphere were shown the altered relative abundance between the control and treated samples depending on genotypes. A genus related to symbiotic nitrogen-fixing bacteria, the Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium clade, showed higher relative abundance among all root samples, indicating that it is a core bacterial genus. Furthermore, the field application of chemical fertilizer had a significant impact on the relative abundances of two genera related to symbiotic nitrogen-fixers, Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium clade and Bradyrhizobium in the rhizosphere and root. These results suggest that N-based chemical fertilizers and plant genotypes would influence the compositional arrangement of associated bacterial communities, including symbiotic nitrogen-fixing bacteria.

Comparative assessment of the effectiveness of contact and systemic fungicides for treating soybean seeds in the forest-steppe of the Novosibirsk Region

The study aimed to evaluate the biological and economic effectiveness of fungicidal soybean disinfectants of different mechanisms of action in a tank mixture with inoculants in the forest-steppe of the Novosibirsk region. The studies were carried out in 2019–2022. Generally accepted methods are used in the conditions of the northern forest steppe of the Novosibirsk region. For the studies, we used the systemic protectant Baritone (prothioconazole 37.5 g/l + fluoxastrobin 37.5 g/l) at a rate of 1.5 l/t and contact Maxim (fludioxonil 25 g/l) at a rate of 2.0 l/t t, the inoculant was HiCoat Super Soybean (HCSS) 1.42 l/t together with the nutrient medium HiCoat Super Extender (HCSE) 1.42 l/t. On average, over four years, the development of soybean root rots, according to the predecessor winter wheat, exceeded the harmfulness threshold in the control variant by 1.3–2.7 times over the years; the maximum indicator was noted in the dry year of 2022 when soybean plants experienced double stress - hydrothermal and biotic. F. oxysporum, F. poae, F. equseti, F. sporotrichioides, and F. solani were isolated from the underground soybean organs during the growing season. The pathogenic complex of soybean root rots also included fungi of the genera Pythium and Rhizoctonia. The biological effectiveness of seed treatment against root rot was 40.2–76.4% and was higher when soybean seedlings developed in moist conditions. The economic efficiency of seed treatment was 103–347% over the years, with a maximum in wet years. The best option for pre-sowing seed treatment is the contact disinfectant Maxim, 2.0 l/t in a tank mixture with the inoculant HiCoat Super Soya (HCSS), 1.42 l/t together with the nutrient medium HiCoat Super Extender (HCSE), 1.42 l/ T. Both fungicidal disinfectants showed a bactericidal effect on symbiotic nitrogen-fixing bacteria, reducing the number of nodules to 43.2% and their weight to 38.1%. Treatment and vaccination of soybean seeds positively affected the quality of the resulting crop. The protein content was the highest in the Baritone variant together with the inoculants HCSS + HCSE and amounted to 41.4% versus 36.8% in the control. Dressing agents had a significant positive effect on the quality of soybean seeds of the new crop; the best aftereffect was found in the Maxim variant, 2.0 l/t + inoculants, where the prevalence of all phytopathogens was below the ETH (economic threshold of harmfulness), and germination was maximum.

Legume rhizodeposition promotes nitrogen fixation by soil microbiota under crop diversification

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

Probing the active site of Class 3 L-asparaginase by mutagenesis. I. Tinkering with the zinc coordination site of ReAV.

ReAV, the inducible Class-3 L-asparaginase from the nitrogen-fixing symbiotic bacterium Rhizobium etli, is an interesting candidate for optimizing its enzymatic potential for antileukemic applications. Since it has no structural similarity to known enzymes with this activity, it may offer completely new ways of approach. Also, as an unrelated protein, it would evade the immunological response elicited by other asparaginases. The crystal structure of ReAV revealed a uniquely assembled protein homodimer with a highly specific C135/K138/C189 zinc binding site in each subunit. It was also shown before that the Zn2+ cation at low and optimal concentration boosts the ReAV activity and improves substrate specificity, which indicates its role in substrate recognition. However, the detailed catalytic mechanism of ReAV is still unknown. In this work, we have applied site-directed mutagenesis coupled with enzymatic assays and X-ray structural analysis to elucidate the role of the residues in the zinc coordination sphere in catalysis. Almost all of the seven ReAV muteins created in this campaign lost the ability to hydrolyze L-asparagine, confirming our predictions about the significance of the selected residues in substrate hydrolysis. We were able to crystallize five of the ReAV mutants and solve their crystal structures, revealing some intriguing changes in the active site area as a result of the mutations. With alanine substitutions of Cys135 or Cys189, the zinc coordination site fell apart and the mutants were unable to bind the Zn2+ cation. Moreover, the absence of Lys138 induced atomic shifts and conformational changes of the neighboring residues from two active-site Ser-Lys tandems. Ser48 from one of the tandems, which is hypothesized to be the catalytic nucleophile, usually changes its hydration pattern in response to the mutations. Taken together, the results provide many useful clues about the catalytic mechanism of the enzyme, allowing one to cautiously postulate a possible enzymatic scenario.

Complete genome sequence of Bradyrhizobium ottawaense strain MIAE 01942 isolated from soybean nodules grown in antibiotic-amended soil.

Bradyrhizobium ottawaense MIAE 01942 is a symbiotic nitrogen-fixing bacterium isolated from the root nodules of soybeans grown in agricultural soils amended with veterinary antibiotics. The genome consists of a single 8.45 Mb circular chromosome that harbors genes involved in nitrogen fixation, denitrification, and antibiotic and metal resistance.

Bio-Efficacy of New Herbicide Molecules for Weed Management in Grain Legumes

Grain legumes including pigeon pea, chickpea, peanut, soybean, lentil, cowpea, common bean, faba bean, pea, and horse gram are extensively cultivated globally. Higher protein content, coupled with symbiotic nitrogen-fixing bacteria in root nodules enabling nitrogen fixation, highlights their importance in minimizing fertilizer use for agricultural production systems. Legume cultivation is limited by prolonged weed interference which is managed either through mechanical, cultural, chemical, or biological methods separately or in combinations. Nevertheless, herbicides remain and will persist as a crucial and economical element in global crop cultivation. While first-generation herbicides benefit agriculture, their long-term persistence and off-target toxicity have significant negative consequences, causing harm to both the environment and humans. Moreover, weed resistance and similar chemistry enforce the demand for new modes of action. Therefore, continuous research into new herbicides is important for combating herbicide resistance and ensuring crop output. In recent years, a few herbicides with novel mechanisms of action have occurred. Plants treated with new-generation herbicides resulted in increased WCE (weed control efficiency), decreased weed dry matter, and seed yield. There were no or minimal phytotoxicity symptoms observed on the existing and succeeding crops. This review emphasizes the importance of newly formulated herbicides signifying high selectivity, low toxicity, target specificity, and minimal application rates, contributing to an enhanced understanding of human and environmental health. Furthermore, it emphasizes the significance of economic viability and environmental friendliness in these formulations.

Nitrogen-fixing Bacteria and their Applications in the Environment: A Review

The process of converting nitrogen into ammonia in the form of a compound is referred to as biological nitrogen fixation. This process is accomplished by various types of nitrogen-fixing bacteria. In this process, atmospheric dinitrogen is enzymatically converted into ammonia by nitrogen-fixing microorganisms. These nitrogen-fixing bacteria are broadly classified into two groups: symbiotic nitrogen-fixing bacteria and non-symbiotic nitrogen-fixing bacteria. Within the microbial cells, ammonia is used for the maintenance and development of the bacterial cells. These microorganisms produce several enzymes, proteins, and cofactors that are essential for the functioning of the key enzyme nitrogenase. This enzyme is capable of reducing inert nitrogen molecules to ammonia. The entire process involves the electron transport chain within the bacterial cell. Two of the many diverse genera of rhizobia, Rhizobium and Bradyrhizobium, are α-proteobacterial diazottrophic families that form root nodules through the interaction of symbiotic genes. The nitrogen-fixing symbionts of actinophytes are symbiotic rhizobia of the genera Mesorhizobium, Sinorhizobium and Bradyrhizobium, such as Azorhizobium. The genera Frankia and Discorrhizobium provide drought-resistant forage roots in non-legume actinophytes such as alder and myrica woodlands. Frankia actinophytes have the ability to live as sugar and cellulose decomposers in addition to being symbiotic with actinophytes. Integrating nitrogen-fixing bacteria into integrated disease management can lead to significant plant growth. Research involving the application of biofertilizers in a variety of crops is at an interactive level. Nitrogen-fixing bacteria can fix nitrogen from the air into the root zone under both free and bonded nitrogen fixation. In some cases, co-inoculation of mycorrhizal spores together with nitrogen-fixing microorganisms and Azospirillum strains has shown improvement in plant health. Nitrogen-fixing bacteria can improve the structure and fertility of soils that have been degraded for various reasons. Therefore, nitrogen-fixing bacteria have the potential to be used in environmental remediation processes to treat wastewater, human and animal waste, or overcome other disinfection caused by industrial pollutants. In environmental nitrogen cycles, the application of nitrogen-fixing bacteria can provide opportunities for the accumulation and preservation of organic matter through different particle sizes. However, it is necessary to identify nitrogen-fixing bacteria endemic to different ecosystems and study the potential biochemical cycles of nitrogen in different sized mineral components. In addition, the efficiency rates of chemical remediation should be compared due to potential problems with the development of concentrations of these microorganisms in environmental restoration or bioremediation processes over large areas. There is hope for the positive development of strategies to eliminate harmful metals in soil and restore potential management profits under the green economy policy, with the preferential use of extreme organisms living within soil elements, which will contribute to different strategies for the use of nitrogen fertilizers in agriculture.

Identification of Native Root Nodulating Bacteria from Mucuna (Mucuna pruriens L.)

Background: Mucuna (Mucuna pruriens L.) is an annual herbaceous climber, grown as a medicinal, green manure, cover and smothering crop. The mucuna seeds contains L-DOPA (L-3, 4 dihydroxy phenylalanine), a non-protein amino acid, extensively used for Parkinson and hypertensive drug. Injudicious application of nitrogenous fertilizers leads to deterioration of soil quality which results into loss of crop yield and quality. The application of microbial inoculant containing efficient native rhizobia enhances the nodular properties, N2-fixation and soil quality. Therefore, Rhizobium strain associated with mucuna was isolated, biochemically characterized and identified. The 16SrRNA sequencing revealed that Sinnorhizobium mililoti, a gram negative symbiotic nitrogen fixing bacteria is present in root nodules of mucuna. Methods: Root nodules were extracted from mucuna grown at ICAR- Krishi Vigyan Kendra, Doddaballapura Taluk, Bengaluru Rural District, Karnataka, then cultured, screened and characterized in the laboratory. The 16SrRNA sequencing and phylogenetic analysis was done to identify the native rhizobial strain. Result: Identification of native root nodulating bacteria through 16SrRNA sequencing concluded that Sinnorhizobium mililoti strain associated with the root nodules of Mucuna (Mucuna pruriens L.).

Nodulation pattern in different legumes by Rhizobia isolated from rajma

Rhizobium is an important symbiotic nitrogen fixing bacteria. The bacteria colonize leguminous plant cells within root nodules, where they convert atmospheric nitrogen into ammonia using the enzyme nitrogenase and then provide organic nitrogenous compounds such as glutamine or ureides to the plant. The plant, in turn, provides the bacteria with organic compounds made by photosynthesis. In this study, rhizosphere soil samples and nodules were collected from rajma plants of hilly Paderu region of Andhra Pradesh. Rhizobia were isolated from these samples using Yeast Extract Manitol Agar (YEMA) medium. There were 5 Rhizobium isolates obtained from the rhizosphere soil and nodules of rajma. These isolates were purified and inoculated to different legumes viz, black gram, green gram, red gram, Bengal gram and groundnut through seed treatment, planted in glass jars and maintained in green house. Nodulation pattern was studied 45 days after sowing. Rhizobium isolates 1 and 5 produced nodules in black gram and green gram, and Rhizobium isolate 2 produced nodules in black gram and red gram. Rhizobium isolate 3 produced nodules in black gram, green gram and red gram, and Rhizobium isolate 4 produced nodules in blackgram, greengram and groundnut. This study clearly showed that there is a possibility for Rhizobium isolate obtained from one legume to form nodules in other legumes but with variation in nodulation pattern.

Biological Efficacy of Plant Growth–Promoting Bacteria and Arbuscular Mycorrhizae Fungi: Assessments in Laboratory and Greenhouse Conditions

Utilizing the interactions of microorganisms with plants offers a favorable path to increase crop production and replace the use of synthetic fertilizers. Different bacteria and fungi have been used as biofertilizers to improve agricultural production, yield, and sustainability. Beneficial microorganisms can act as free-living organisms, symbiotes, and endophytes. Soil bacteria called plant growth-promoting bacteria (PGPB) and fungi called arbuscular mycorrhizae fungi (AMF) stimulate the growth and health of plants by direct and indirect mechanisms including nitrogen fixation, phosphorus solubilization, phytohormone production, enzyme production, antibiotic synthesis, and induced systemic resistance. To use these microorganisms as a biofertilizer, it is necessary to assess their efficacy under laboratory and greenhouse conditions. Few reports detail the methods used to develop a test under different environmental conditions, and without these details it is difficult to develop suitable methodologies to evaluate microorganism-plant relationships. We describe four protocols that go from sample preparation to testing in vitro the efficacy of different biofertilizers. Each protocol can be used to test a different biofertilizer microorganism, focusing on bacteria such as Rhizobium sp., Azotobacter sp., Azospirillum sp., Bacillus sp. as well as AMF such as Glomus sp. These protocols can be used in several stages of biofertilizer development, including microorganism selection, microorganism characterization, and in vitro evaluation of efficacy for the registration process. © 2023 Wiley Periodicals LLC. Basic Protocol 1: Evaluating the biological effect of biofertilizer based on PGPB under laboratory conditions Basic Protocol 2: Evaluating the biological effect of biofertilizer based on PGPB under greenhouse conditions Basic Protocol 3: Evaluating the biological effect of biofertilizer based on symbiotic nitrogen-fixing bacteria Basic Protocol 4: Evaluating the biological effect of biofertilizer based on AMF.

Co-inoculation of Bradyrhizobium and Phosphate Solubilizing Microbes on Growth Promotion of Groundnut Under Rain-fed Conditions

Plant growth-promoting bacteria (PGPB) can improve plant development and protect plants from diseases and abiotic stresses. Plant-bacterial interactions in the rhizosphere are important factors in soil fertility and plant health. Symbiotic nitrogen-fixing bacteria include the cyanobacteria of the genera Rhizobium, Bradyrhizobium, Azorhizobium, Allorhizobium, Sinorhizobium and Mesorhizobium. Therefore, to investigate the effect of co-inoculation of Bradyrhizobium and phosphate solubilizing microbes (PSM) on groundnut crop under field conditions using normal soil, divided into eight different study groups i.e., control (T1), Bradyrhizobium isolate -1 (T2), Bradyrhizobium isolate -2 (T3), Bradyrhizobium isolate -3(T4), Phosphate solubilizing microbe (PSM) (T5), T2 + PSM (T6), T3 + PSM (T7), T4 + PSM (T8). The results showed maximum groundnut pod yield (2428 kg ha-1) was obtained in treatment where inoculation with bacterial isolate-2 applied as compared to control. In case of plant height and shoot dry biomass, maximum response was observed in T7 (59.4 cm, 4733 kg ha-1) as compared to control i.e., 40.5 cm, 3156.7 kg ha-1 respectively. It was concluded that this technique might be useful and applicable to cut down the high input cost of phosphate fertilizers for the production of other crops also

Nitrogen-fixing symbiotic bacteria act as a global filter for plant establishment on islands

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.

Rhizobia exopolysaccharides: promising biopolymers for use in the formulation of plant inoculants.

Inoculants with beneficial microorganisms comprise both selected strains and carriers that ensure a favorable microenvironment for cell survival and stability. Formulations of inoculants using synthetic polymers as carriers are common. However, only a few studies are available in the literature regarding the formulation of inoculants using natural biomolecules as carriers. Exopolysaccharides (EPS) are biomolecules produced by a vast array of microbial species, including symbiotic nitrogen-fixing bacteria, commonly known as rhizobia. EPS perform several functions, such as the protection against the deleterious effects of diverse environmental soil stresses. Two Rhizobium tropici strains and one Paraburkholderia strain were selected after semiquantitative analysis by scanning electron microscopy (SEM) of their EPS production in liquid YMA medium. Their EPS were characterized through a series of analytical techniques, aiming at their use in the formulation of plant inoculants. In addition, the effect of the carbon source on EPS yield was evaluated. Multi-stage fragmentation analysis showed the presence of xylose, glucose, galactose, galacturonic acid, and glucuronic acid in EPS chemical composition, which was confirmed by FT-IR spectra and 13C NMR spectroscopy. Thermal stability (thermogravimetric) was close to 270°C and viscosity ranged from 120 to 1053.3mPa.s. Surface morphology (SEM) was rough and irregular, with a cross-linked spongy matrix, which, together with the hydrophilic functional groups, confers water holding capacity. The present study showed that the three EPS have potential as microorganism carriers for formulation of microbial inoculants to be applied in plants.

Novel lineages of single-stranded DNA phages that coevolved with the symbiotic bacteria Rhizobium.

This study describes novel single-stranded DNA phages isolated from common bean agriculture soils by infection of the nitrogen-fixing symbiotic bacteria Rhizobium etli and R. phaseoli. A total of 29 phages analyzed have 4.3–6 kb genomes in size and GC 59–60%. They belong to different clades unrelated to other Microviridae subfamilies. Three-dimensional models of the major capsid protein (MCP) showed a conserved β-barrel structural “jelly-roll” fold. A variable-length loop in the MCPs distinguished three Rhizobium microvirus groups. Microviridae subfamilies were consistent with viral clusters determined by the protein-sharing network. All viral clusters, except for Bullavirinae, included mostly microviruses identified in metagenomes from distinct ecosystems. Two Rhizobium microvirus clusters, chaparroviruses, and chicoviruses, were included within large viral unknown clusters with microvirus genomes identified in diverse metagenomes. A third Rhizobium microvirus cluster belonged to the subfamily Amoyvirinae. Phylogenetic analysis of the MCP confirms the divergence of the Rhizobium microviruses into separate clades. The phylogeny of the bacterial hosts matches the microvirus MCP phylogeny, suggesting a coevolutionary history between the phages and their bacterial host. This study provided essential biological information on cultivated microvirus for understanding the evolution and ecological diversification of the Microviridae family in diverse microbial ecosystems.

CASE STUDY OF SOYBEAN INOCULATION WITH BIOTECHNOLOGICAL PREPARATIONS

Soybean is a powerful biological fixer of molecular nitrogen. Increasing the intensification of nitrogen fixation of the culture is facilitated by inoculation – the settlement of the root zone with effective strains of symbiotic nodule bacteria. Bubble symbiotic bacteria fix molecular nitrogen and transform it into a form available for cultures. Also, nodule bacteria synthesize amino acids and vitamins of group B and other biologically active substances, which in general has a positive effect on the growth and development of soybeans and ensures high crop productivity. Peculiarities of the interaction of leguminous plants and nodule bacteria in field conditions depend on a number of factors, such as the genotype of plants, species composition, the number and activity of nitrogen fixers, the properties of soils, their water and temperature regimes, and the level of agricultural technology.&#x0D; The effectiveness of soybean inoculation with biotechnological preparations based on nitrogen-fixing microorganisms was analyzed. In Ukraine, a number of biotechnological preparations on the basis of nodule bacteria such as Nitragin, Rhizotrophin, Rhizoaktiv, Rhizobophyte, Rhizohumin, Azotophyte, Azorchis have been created and tested. According to the results of the scientific literature analysis and the conducted research, a positive effect of biotechnological preparations use on the formation of nodules on soybean roots and the increase in the intensity of nitrogen fixation was established. Positive changes in the indicators of the crop yield structure under the influence of inoculation were also monitored. It has been confirmed that the productivity of soybeans has increased due to the biotechnological preparations use based on symbiotic nitrogen-fixing bacteria. It has been proven that the inoculation of soybeans with biotechnological preparations is an effective measure that ensures an increase in the productivity of soybeans, an improvement in the quality of the obtained products, contributes to the intensification of the formation of nodules on the roots, and as a result, enhances the fixation of atmospheric nitrogen.