Rhizobium Research Articles

Development, characterization and evaluation of in vitro safety and in vivo efficacy of repellent gel formulations

Contagious diseases caused by mosquito bites are responsible for epidemic outbreaks around the world. Applying mosquito repellents is the main and most cost-effective prophylactic measure to reduce the transmission risk of arboviruses. In this study, two topical gel Formulations were developed as mosquito repellents which use two different systems to release 20 % Icaridin. The first, Formulation 1b uses Pluronic F127®, and the second, Formulation 2b uses a biopolymer produced by bacteria from the Rhizobium tropici species. The repellent Formulations developed showed non-Newtonian behavior. For Formulation 1b the viscosity increased after adding Icaridin. However, for Formulation 2b, there was no increase in viscosity after adding the active substance. The thixotropy analysis showed that the Formulations have good recovery of their structure and adhesion. Adding of Icaridin led to an increase in gel strength in Formulation 1b and did not change the gel strength for Formulation 2b. The Formulations presented very similar occlusion capacities which were all higher than free Icaridin. The Formulations were not cytotoxic in the concentration range between 0.04 % and 0.3 %. In addition, at the 0.62 % concentration, they showed a slight reduction in cell viability, although the LD50 value was not reached. The mean protection time was longer for Formulation 2b compared to Formulation 1b. Both Formulations had a longer mean protection time than free Icaridin against Aedes aegypti. The combination of Icaridin with Pluronic F127® and the biopolymer is an innovation in the pharmaceutical area.

Characterization of Plant Growth Promoting Rhizobacteria and Their Benefits on Soybean Growth

Background: Soybean is the most important legume in the world and its seeds contains 40% protein and 20% oil. In recent years, more attention has been paid to the use of plant growth-promoting (PGP) rhizobacteria as a biofertilizer alternative to chemical fertilizers, which may pose risks to the environment. The rhizobia inoculation of soybean is a sustainable practice to induce atmospheric nitrogen fixation and subsequently improve crop productivity and soil fertility. Methods: In this study, 19 indigenous rhizobia isolated from soybean were tested in vitro for their plant growth-promoting properties (PGPR), while genotypic characterization included sequencing of the 16S rRNA gene. Result: Morphological characterisation has shown that all of the isolates were rod-shaped gram negative bacteria. The sequencing has shown that 12 out of 19 isolates belong to the genus Pseudomonas, four of which belong to P. fluorescens species. Isolates which belong to the Pseudomonas genus have shown the highest ability of indole-3-acetic acid synthesis, phosphorous solubilization and along with isolates SGN6, SGN7 and SGS4 (Sphingomonas sanguinis) potassium solubilisation too. All the isolates from Pseudomonas genus as well as those belonging to B. japonicum species have shown the protease synthesis abilities while amylase synthesis abilities was observed only in the isolate SAK2 (P. chlororaphis). The most efficient strains in in vitro biological nitrogen fixation assay belong to Pseudomonas and Rhizobium genera. Most of the isolates were positive to the organic acid production while all of them have shown the ability of the exopolysaccharide production.

Phylogenetic diversity of Rhizobium species recovered from nodules of common beans (Phaseolus vulgaris L.) in fields in Uganda: R. phaseoli, R. etli, and R. hidalgonense.

A total of 75 bacterial isolates were obtained from nodules of beans cultivated across 10 sites in six agro-ecological zones in Uganda. Using recA gene sequence analysis, 66 isolates were identified as members of the genus Rhizobium, while nine were related to Agrobacterium species. In the recA gene tree, most Rhizobium strains were classified into five recognized species. Phylogenetic analysis based on six concatenated sequences (recA-rpoB-dnaK-glnII-gyrB-atpD) placed 32 representative strains into five distinct Rhizobium species, consistent with the species groups observed in the recA gene tree: R. phaseoli, R. etli, R. hidalgonense, R. ecuadorense, and R. sophoriradicis, with the first three being the predominant. The rhizobial strains grouped into three nodC subclades within the symbiovar phaseoli clade, encompassing strains from distinct phylogenetic groups. This pattern reflects the conservation of symbiotic genes, likely acquired through horizontal gene transfer among diverse rhizobial species. The 32 representative strains formed symbiotic relationships with host beans, while the Agrobacterium strains did not form nodules and lacked symbiotic genes. Multivariate analysis revealed that species distribution was influenced by the environmental factors of the sampling sites, emphasizing the need to consider these factors in future effectiveness studies to identify effective nitrogen-fixing strains for specific locations.

Rhizobium etli CFN42 and Sinorhizobium meliloti 1021 bioinformatic transcriptional regulatory networks from culture and symbiosis.

Rhizobium etli CFN42 proteome-transcriptome mixed data of exponential growth and nitrogen-fixing bacteroids, as well as Sinorhizobium meliloti 1021 transcriptome data of growth and nitrogen-fixing bacteroids, were integrated into transcriptional regulatory networks (TRNs). The one-step construction network consisted of a matrix-clustering analysis of matrices of the gene profile and all matrices of the transcription factors (TFs) of their genome. The networks were constructed with the prediction of regulatory network application of the RhizoBindingSites database (http://rhizobindingsites.ccg.unam.mx/). The deduced free-living Rhizobium etli network contained 1,146 genes, including 380TFs and 12 sigma factors. In addition, the bacteroid R. etli CFN42 network contained 884 genes, where 364 were TFs, and 12 were sigma factors, whereas the deduced free-living Sinorhizobium meliloti 1021 network contained 643 genes, where 259 were TFs and seven were sigma factors, and the bacteroid Sinorhizobium meliloti 1021 network contained 357 genes, where 210 were TFs and six were sigma factors. The similarity of these deduced condition-dependent networks and the biological E. coli and B. subtilis independent condition networks segregates from the random Erdös-Rényi networks. Deduced networks showed a low average clustering coefficient. They were not scale-free, showing a gradually diminishing hierarchy of TFs in contrast to the hierarchy role of the sigma factor rpoD in the E. coli K12 network. For rhizobia networks, partitioning the genome in the chromosome, chromids, and plasmids, where essential genes are distributed, and the symbiotic ability that is mostly coded in plasmids, may alter the structure of these deduced condition-dependent networks. It provides potential TF gen-target relationship data for constructing regulons, which are the basic units of a TRN.

O-Methylated Isoflavones Induce nod Genes of Mesorhizobium ciceri and Pratensein Promotes Nodulation in Chickpea.

Legume plants form symbiotic relationships with rhizobia, which allow plants to utilize atmospheric nitrogen as a nutrient. This symbiosis is initiated by secretion of specific signaling metabolites from the roots, which induce the expression of nod genes in rhizobia. These metabolites are called nod gene inducers (NGIs), and various flavonoids have been found to act as NGIs. However, NGIs of chickpea, the second major pulse crop, remain elusive. We conducted untargeted metabolome analysis of chickpea root exudates to explore metabolites with increased secretion under nitrogen deficiency. Principal component (PC) analysis showed a clear difference between nitrogen deficiency and control, with PC1 alone accounting for 37.5% of the variance. The intensity of two features with the highest PC1 loading values significantly increased under nitrogen deficiency; two prominent peaks were identified as O-methylated isoflavones, pratensein and biochanin A. RNA-seq analysis showed that they induce nodABC gene expression in the Mesorhizobium ciceri symbiont, suggesting that pratensein and biochanin A are chickpea NGIs. Pratensein applied concurrently with M. ciceri at sowing promoted chickpea nodulation. These results demonstrate that pratensein and biochanin A are chickpea NGIs, and pratensein can be useful for increasing nodulation efficiency in chickpea production.

Unearthing Optimal Symbiotic Rhizobia Partners from the Main Production Area of Phaseolus vulgaris in Yunnan.

Phaseolus vulgaris is a globally important legume cash crop, which can carry out symbiotic nitrogen fixation with rhizobia. The presence of suitable rhizobia in cultivating soils is crucial for legume cropping, especially in areas beyond the plant-host native range, where soils may lack efficient symbiotic partners. We analyzed the distribution patterns and traits of native rhizobia associated with P. vulgaris in soils of Yunnan, where the common bean experienced a recent expansion. A total of 608 rhizobial isolates were tracked from soils of fifteen sampling sites using two local varieties of P. vulgaris. The isolates were discriminated into 43 genotypes as defined by IGS PCR-RFLP. Multiple locus sequence analysis based on recA, atpD and rpoB of representative strains placed them into 11 rhizobial species of Rhizobium involving Rhizobium sophorae, Rhizobium acidisoli, Rhizobium ecuadorense, Rhizobium hidalgonense, Rhizobium vallis, Rhizobium sophoriradicis, Rhizobium croatiense, Rhizobium anhuiense, Rhizobium phaseoli, Rhizobium chutanense and Rhizobium etli, and five unknown Rhizobium species; Rhizobium genosp. I~V. R. phaseoli and R. anhuiense were the dominant species (28.0% and 28.8%) most widely distributed, followed by R. croatiense (14.8%). The other rhizobial species were less numerous or site-specific. Phylogenies of nodC and nifH markers, were divided into two specific symbiovars, sv. phaseoli regardless of the species affiliation and sv. viciae associated with R. vallis. Through symbiotic effect assessment, all the tested strains nodulated both P. vulgaris varieties, often resulting with a significant greenness index (91-98%). However, about half of them exhibited better plant biomass performance, at least on one common bean variety, and two isolates (CYAH-6 and BLYH-15) showed a better symbiotic efficiency score. Representative strains revealed diverse abiotic stress tolerance to NaCl, acidity, alkalinity, temperature, drought and glyphosate. One strain efficient on both varieties and exhibiting stress abiotic tolerance (BLYH-15) belonged to R. genosp. IV sv. phaseoli, a species first found as a legume symbiont.

Diverse bacterial consortia: key drivers of rhizosoil fertility modulating microbiome functions, plant physiology, nutrition, and soybean grain yield

Soybean cultivation in tropical regions relies on symbioses with nitrogen-fixing Bradyrhizobium and plant growth-promoting bacteria (PGPBs), reducing environmental impacts of N fertilizers and pesticides. We evaluate the effects of soybean inoculation with different bacterial consortia combined with PGPBs or microbial secondary metabolites (MSMs) on rhizosoil chemistry, plant physiology, plant nutrition, grain yield, and rhizosphere microbial functions under field conditions over three growing seasons with four treatments: standard inoculation of Bradyrhizobium japonicum and Bradyrhizobium diazoefficiens consortium (SI); SI plus foliar spraying with Bacillus subtilis (SI + Bs); SI plus foliar spraying with Azospirillum brasilense (SI + Az); and SI plus seed application of MSMs enriched in lipo-chitooligosaccharides extracted from B. diazoefficiens and Rhizobium tropici (SI + MSM). Rhizosphere microbial composition, diversity, and function was assessed by metagenomics. The relationships between rhizosoil chemistry, plant nutrition, grain yield, and the abundance of microbial taxa and functions were determined by generalized joint attribute modeling. The bacterial consortia had the most significant impact on rhizosphere soil fertility, which in turn affected the bacterial community, plant physiology, nutrient availability, and production. Cluster analysis identified microbial groups and functions correlated with shifts in rhizosoil chemistry and plant nutrition. Bacterial consortia positively modulated specific genera and functional pathways involved in biosynthesis of plant secondary metabolites, amino acids, lipopolysaccharides, photosynthesis, bacterial secretion systems, and sulfur metabolism. The effects of the bacterial consortia on the soybean holobiont, particularly the rhizomicrobiome and rhizosoil fertility, highlight the importance of selecting appropriate consortia for desired outcomes. These findings have implications for microbial-based agricultural practices that enhance crop productivity, quality, and sustainability.Graphical

Bacterial genera associated with nitrogen cycle in microbial communities of chernozems

BACKGROUND: Reactions associated with the geochemical nitrogen cycle occurring in the soil have a decisive effect on the level of nitrogen availability for green plants. Microorganisms that catalyze them are of interest from the point of view of developing mechanisms for managing soil fertility. In this paper, we focused on bacterial genera associated with nitrogen cycle processes in chernozem soils of the Belgorod Region of Russia. AIM: To determine the list and quantitative ratios of bacterial genera whose representatives are able to participate in the fixation of atmospheric nitrogen, nitrification and denitrification in the chernozems of the forest-steppe zone of the European part of Russia. MATERIALS AND METHODS: Samples of arable and non-arable chernozems of three subtypes were collected in June and August 2022. Microbiological profiling based on high-throughput sequencing of amplicons of V3 and V4 region of the 16S rRNA gene with subsequent computational processing of the results was used in the work. RESULTS: 6 genera of nitrogen-fixing bacteria were found, as well as a group undifferentiated by means of the method used, including genus Rhizobium. 8 genera involved in the first and 5 genera involved in the second stage of nitrification were also found. 7 genera have been found whose representatives are capable of denitrification, without taking into account nitrogen-fixing bacteria, which are also capable of carrying out this process. CONCLUSIONS: Among the bacteria capable of fixing atmospheric nitrogen in the chernozems of the Belgorod region, the genus Bradyrhizobium dominates. Among the nitrifiers performing the first stage of nitrification, Ellin6067 and MND1 from the family Nitrosomonadaceae predominate. The second stage of nitrification is carried out mainly by bacteria of the genus Nitrospira. Of the potential denitrifies, along with nitrogen-fixing genera possessing this ability, representatives of the genera Rubrobacter and Pseudomonas are the most numerous. The study does not claim to give a complete list of organisms that carry out key chemical transformations of nitrogen compounds in chernozems, however, it allows us to name their important participants.

Exopolysaccharides from Rhizobium Tropici mitigate aluminum bioaccumulation and toxicity in earthworm Lumbricus Terrestris

Aluminum is one of the most abundant elements in earth’s crust and soils. Global soil acidification has occurred with industrialization and enhances Al solubility in acidic soils, resulting in Al phytoxicity and reducing crop production. Earthworms play an important role in nutrient recycling in soils and maintaining soil health. Rhizosphere microorganism excretes exopolysaccharides (EPS) into the rhizosphere. The objectives of this study is to examine effects of EPS from Rhizobium Tropici on aluminum uptake and ecotoxicity to earthworms in soils and litters. Overall this study provides the scientific understanding of the EPS in alleviation of Al toxicity to earthworms in soils. Results showed the clear mitigation of EPS in reducing earthworm mortality rate and increasing its reproductivity under Al stress. EPS significantly decreased Al uptake from soil and litters, and decreased Al in subcellular distribution (cell membrane, cytosol and organelle fractions) in earthworms from soils. Al in purges was found to be mainly present in the residual fraction, while EPS slightly increased Al in water soluble and exchangeable fractions in purges. Overall water soluble and organic matter bound Al in soils were correlated well with Al in earthworms, but Al in earthworms were controlled by total Al in purges. The current study concluded that earthworm Lumbricus Terrestre may be a potential bio-indicator of Al ecotoxicity in soils and EPS from Rhizobium Tropici effectively mitigated Al ecotoxicity in soils.

Diversity and Phylogeny of Symbiotic Bacteria Nodulating Common Bean (Phaseolus vulgaris L.) in Côte d’Ivoire

Phaseolus vulgaris L. (common bean) is an agriculturally important legume that benefits from a symbiosis with bacteria belonging to the genus Rhizobium. Growing interest in the use of rhizobia as biofertilizers has led to the identification of a large number of rhizobia strains and studies of their diversity. Although much research has been carried out on rhizobia, there is little data on the diversity of rhizobia associated with common bean in Côte d'Ivoire. This study assessed the species diversity of common bean nodulating bacteria in ivorian soils. This diversity was assessed based on 16S rRNA gene sequencing. Ten high-performance bacterial isolates extracted from common bean nodules were used for genetic analysis. The 16S rRNA gene sequences of the native isolates were closely affiliated with members of the genera Rhizobium, Bradyrhizobium, Allorhizobium and Sinorhizobium demonstrating the presence of a diversity of native bean nodule bacteria. This study also reports for the first time the presence of Allorhizobium taibaishanense in common bean nodules. These results constitute an important step in the development of an effective microbial inoculum and sustainable food production.

Altitude-dependent influence of Artemisia brevifolia on its rhizosphere microbiome in Ladakh region of the Western Himalayas

Altitude-induced variations significantly influence plant physiology, shaping the diversity and composition of prokaryotic and fungal communities in the rhizosphere soil. This study investigates the impact of altitude on the rhizosphere microbiome of Artemisia brevifolia in the Ladakh region of the Western Himalayas. Alpha diversity indices reveal a decline in both prokaryotic and fungal diversity in rhizosphere soil compared to bulk soil, with a more pronounced effect on prokaryotic communities at different altitudes. Altitude variation significantly impacts prokaryotic and fungal beta-diversity, leading to distinct microbial communities at different elevations. Notably, the rhizosphere communities at higher altitudes exhibit little overlap with bulk soil communities, indicating a unique microbial assemblage possibly in response to harsh environmental conditions. The dominant prokaryotic phyla include Actinobacteriota, Proteobacteria, Chloroflexi, and Acidobacteriota, while the fungal communities are dominated by Ascomycota and Basidiomycota. A significantly higher frequency of rhizobia was noted in the A. brevifolia rhizosphere at both locations, with the genus Rhizobium prevalent at lower altitudes and Mesorhizobium at the higher altitudes. Predicted functions of prokaryotic communities revealed a higher abundance of pathways associated with the biosynthesis of siderophores, secondary metabolites and aromatic-compounds, and denitrification in the rhizosphere. Additionally, a higher abundance of gene clusters associated with nitrogen fixation and phosphorus metabolisms was noted in rhizosphere particularly at higher elevations.In summary, this comprehensive study highlights the unique structure and function of microbial communities along increasing elevations, particularly in the rhizosphere, potentially aiding the host plant in thriving under the stressful conditions of high altitudes in the climate-sensitive Himalayas.

Role of core lipopolysaccharide biosynthetic genes in the infection and adsorption of broad-host-range bacteriophages of Rhizobium etli.

In this study, we examined the role of the lipopolysaccharide (LPS) core of Rhizobium etli in facilitating the adsorption and infection of phages with broad host range. When the plasmid-encoded LPS biosynthesis genes, wreU and wreV, were disrupted, distinct and contrasting effects on phage infection were observed. The wreU mutant strains exhibited wild-type adsorption and infection properties, whereas the wreV mutant demonstrated resistance to phage infection, but retained the capacity to adsorb phages. Complementation of the wreV mutant strains with a recombinant plasmid containing the wreU and wreV, restored the susceptibility to the phages. However, the presence of this recombinant plasmid in a strain devoid of the native lps-encoding plasmid was insufficient to restore phage susceptibility. These results suggest that the absence of wreV impedes the proper assembly of the complete LPS core, potentially affecting the formation of UDP-KdgNAg or KDO precursors for the O-antigen. In addition, a protein not yet identified, but residing in the native lps-encoding plasmid, may be necessary for complete phage infection.

The symbiovar mediterranense of Sinorhizobium meliloti nodulates Phaseolus vulgaris across Lanzarote (Canary Islands): A revision of this symbiovar supports a proposal to delimit symbiovars boundaries in Sinorhizobium and to define four new symbiovars

The symbiovar mediterranense of Sinorhizobium meliloti was initially found in Phaseolus vulgaris nodules in Tunisia and in an eastern location of Lanzarote (Canary Islands). Here we show that the symbiovar mediterranense of S. meliloti also nodulates P. vulgaris in two western locations of this Island. The analyses of the symbiotic nodA and nodC genes reveal the complexity of the symbiovar mediterranense which encompasses strains belonging to several phylogenetic lineages and clusters. The comparison of the nodA and nodC phylogenies showed that the nodC was the most resolutive phylogenetic marker for the delineation of Sinorhizobium symbiovars. Considering that the similarity of this gene within several symbiovars, particularly mediterranense, is around 95 %, the cut-off value for their differentiation should be lower. Considering that a nodC gene cut-off similarity value of around 92 % is accepted for the genus Bradyrhizobium and that the symbiovar concept is identical in all rhizobial genera, we propose to apply this value for symbiovars delineation within all these genera. Therefore, using this cut-off value for the nodC gene analysis of Sinorhizobium symbiovars, we propose to merge the symbiovars aegeanense and fredii into the single symbiovar fredii and to define four novel symbiovars with the names asiaense, culleni, sudanense and tunisiaense.

The rhizosphere of a drought-tolerant plant species in Morocco: A refuge of high microbial diversity with no taxon preference.

Arid and semi-arid areas are facing increasingly severe water deficits that are being intensified by global climate changes. Microbes associated with plants native to arid regions provide valuable benefits to plants, especially in water-stressed environments. In this study, we used 16S rDNA metabarcoding analysis to examine the bacterial communities in the bulk soil, rhizosphere and root endosphere of the plant Malva sylvestris L. in Morocco, along a gradient of precipitation. We found that the rhizosphere of M. sylvestris did not show significant differences in beta-diversity compared to bulk soil, although, it did display an increased degree of alpha-diversity. The endosphere was largely dominated by the genus Rhizobium and displayed remarkable variation between plants, which could not be attributed to any of the variables observed in this study. Overall, the effects of precipitation level were relatively weak, which may be related to the intense drought in Morocco at the time of sampling. The dominance of Rhizobium in a non-leguminous plant is particularly noteworthy and may permit the utilization of this bacterial taxon to augment drought tolerance; additionally, the absence of any notable selection of the rhizosphere of M. sylvestris suggests that it is not significatively affecting its soil environment.

Trichoderma harzianum enhances root biomass production and promotes lateral root growth of soybean and common bean under drought stress

AbstractDrought stress (DS) is one of the main environmental stresses that determines crop productivity. It has been estimated that DS depresses over 40%–60% of soybean (Glycine max (L.) Merr.) and common bean (Phaseolus vulgaris L.) production worldwide, respectively. Although different agronomic strategies are sometimes implemented, the current goal in sustainable agriculture could involve the inoculation with native microorganisms to mitigate DS effects. A potential fungal candidate is Trichoderma, which is recognized as a ubiquitous soil inhabitant with growth‐promoting and biocontrol potentiality. However, its potential for mitigating the stress for water deficit is less well‐documented. Our objective was to evaluate the effect of inoculation with native Trichoderma harzianum strains on soybean and common bean growth under contrasting conditions of water availability. Seeds were independently inoculated (or not) with IB‐J15 and IB‐363 strains, and plants were submitted to DS or were kept under optimal irrigation (well‐watered, WW). In both legumes, the most evident effect after being inoculated was the modification of plant root architecture, the increase in root area and the development of lateral roots in plants under WW and DS conditions. In soybean, both Trichoderma strains had a positive inoculation response, both fresh and dry root biomass increased under WW, and remarkably under DS conditions. The main effect was an increase of about 110% in root dry weight under WW and, about 330% in DS in plants inoculated with IB‐J15 strain, meanwhile, plants inoculated with IB‐363 increased root dry weight 60% in WW and 177% in DS conditions. Notably in soybean, the inoculation with both Trichoderma strains increased the root area more than 70% in both WW and DS conditions. Common beans inoculated with IB‐363 under WW conditions, reached a positive inoculation responsiveness of around 247% in shoot dry weight biomass, and under WW both strains increased the root area more than 50%. Further, IB‐363 increased leaf area by 25% in WW and 72% in DS. Additionally, the in vitro co‐culture between both Trichoderma strains and nodulating Rhizobium etli and Bradyrhizobium japonicum E109 showed compatibility between microorganisms, since no inhibition of their growth was observed. We emphasize that plants inoculated with Trichoderma showed better resistance to water deficit, as seen by redistribution of photosynthates, prioritizing mainly, the development of the root system. © 2024 Association of Applied Biologists.

Bioprospecting of Rhizobia as Plant Growth Promoting Rhizobacteria Potential from Root Nodules of Groundnut (Arachis hypogaea L.)

Rhizobia are bacteria that symbiosis with host plant, as shown in the root nodules formation, and provide nitrogen that can be absorbed by plants in greater quantities than rhizobacteria. Available Nitrogen, which absorbed by plants, is the essential requirement for plant growth because its role in increasing yield and quality, hence it is needed in greater quantities than other nutrients. The study aimed to determine the macroscopic and microscopic diversity of rhizobia isolates from the groundnut nodules and their potential as PGPRs, and to identify 16S rRNA isolates with the best potential as PGPRs molecularly. The methods used were isolation from root nodules, screening of PGPR potential, molecular identification based on the 16S rRNA gene, and phylogenetic analysis to determine their kinship. Based on the isolation results, 17 Gram-negative isolates were obtained white to pink or orange color on AG media with various colony characteristics in terms of shape, margin, elevation, and texture. KT 20, which was selected as rhizobia isolate with the best potential as PGPR, has ammonium concentration of 23.12 ppm, synthesizes IAA with a concentration of 10.36 ppm, and phosphates solubilization activity, although its ability to synthesize proteases is low. The results of molecular identification of 16S rRNA showed that KT 20 belongs to the Rhizobium genus with a similarity of 99.48 % and bootstrap value of 96 %. HIGHLIGHTS Isolate KT 20 (identified rhizobia) has excellent ability in fixing nitrogen, which plants needs the most and legumes requires in large number Beside the ability of Isolate KT 20 to fix nitrogen, it also able to synthesize IAA, solubilize phosphate, and synthesize protease The ability of isolate KT 20 as PGPR was equal or better than other rhizobacteria that has been analyzed in other in vitro studies GRAPHICAL ABSTRACT

The gap gene of Rhizobium etli is required for both free life and symbiosis with common beans.

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH or Gap) is a ubiquitous enzyme essential for carbon and energy metabolism in most organisms. Despite its primary role in sugar metabolism, GAPDH is recognized for its involvement in diverse cellular processes, being considered a paradigm among multifunctional/moonlighting proteins. Besides its canonical cytoplasmic location, GAPDH has been detected on cell surfaces or as a secreted protein in prokaryotes, yet little is known about its possible roles in plant symbiotic bacteria. Here we report that Rhizobium etli, a nitrogen-fixing symbiont of common beans, carries a single gap gene responsible for both GAPDH glycolytic and gluconeogenic activities. An active Gap protein is required throughout all stages of the symbiosis between R. etli and its host plant Phaseolus vulgaris. Both glycolytic and gluconeogenic Gap metabolic activities likely contribute to bacterial fitness during early and intermediate stages of the interaction, whereas GAPDH gluconeogenic activity seems critical for nodule invasion and nitrogen fixation. Although the R. etli Gap protein is secreted in a c-di-GMP related manner, no involvement of the R. etli gap gene in c-di-GMP related phenotypes, such as flocculation, biofilm formation or EPS production, was observed. Notably, the R. etli gap gene fully complemented a double gap1/gap2 mutant of Pseudomonas syringae for free life growth, albeit only partially in planta, suggesting potential specific roles for each type of Gap protein. Nevertheless, further research is required to unravel additional functions of the R. etli Gap protein beyond its essential metabolic roles.

The Effects of Rhizobium Phaseoli and Phosphate-Solubilizing Microorganisms on Phaseolus Vulgaris Amended with Rock Phosphate and Biogas Spent Slurry

Phaseolusvulgaries seeds were inoculated with Rhizobium phaseoli, Phosphate solubilizing Microorganisms (PSM) with rock phosphate in plots containing poultry droppings slurry of biogas plant. This experiment was carried out in 4 treatments with control (T1, T2, T3, T4 and T0).The samples were collected at seedling, preflowering, blooming and end stages to learn the phenotypical nature, NPK and chlorophyll contents. Studies on microbes have also been conducted on plants at every stage of development. Comparing the plant supplied by R.phaseous PSM with rock phosphate to control and other application combinations, the results showed that the plant recorded the highest values in the morphological, biochemical, and microbiological features.From the seedling stage on, the plants' NPK content also rose. (1.262%, 0.28% & 0.26%) to the flowering stage. In the T4 treatment, there are likewise 36 nodules, and each nodule weighs 0.268 g. The weight is roughly 0.039g, and the lowest nodule number (07nos) was discovered in the control. The enriched manure that produced the best results was the combination of SPDS+PSM+RP+R.phaseoli (T4). The yield was 2.435tons/hectare and PSM+RP (T2), which produced 1.890 tons/hectare; PSM+RP (T3), 1.101 tons/hectare in inorganic manure (T1), and control (0.821 tons/hectare) (T0). The study report highlighted the critical roles that PSO, R. phaseoli, and rock phosphate played in P. vulgaries nodulation, nitrogen fixation, and good yield.

Bacteria from nodules of Abrus mollis Hance: genetic diversity and screening of highly efficient growth-promoting strains.

Abrus mollis Hance. (AM) is an important species used in southern Chinese medicine. It is mainly found in Guangdong and Guangxi provinces in China, and it is effective in the treatment of hepatitis. Endophytic bacteria are known to affect the growth and quality of medicinal plants. However, there are limited reports describing endophytic bacteria related to AM. In the present study, Illumina-based 16S rRNA gene sequencing was used to investigate the endophytic bacterial communities of root nodules of AM at five sampling sites in Guangxi. In addition, 179 strains of endophytic bacteria were isolated and categorized into 13 haplotypes based on recA sequence analysis. The phylogeny of the 16S rRNA gene sequences revealed a predominance of nonrhizobial endophytes. Microbial diversity analysis showed that Proteobacteria was the dominant phylum in all samples, while Bradyrhizobium was the dominant genus in different samples. An efficient strain, Rhizobium tropici FM-19, was screened and obtained through greenhouse experiments. The AM plants inoculated with this strain showed the best growth performance and high nitrogen fixation and nodulation capacity. Notably, total phenols and total flavonoids, important active components in AM, increased by 30.9 and 42.7%, respectively, after inoculation with Rhizobium tropici FM-19. This study provides insights into the complex microbial diversity of AM nodules and provides strain information for the efficient cultivation of AM.

Impact of microbial consortium of Rhizobium tropici and Rhizobium mayense on the growth of Phaseolus vulgaris L.

The main objectives of the present investigation was to characterize and recognize potential indigenous Rhizobium spp. associated with red clover nodules, as well as to evaluate the influence of prospective rhizobia inoculation (individual and consortia) on common bean plant growth. Total of 8 rhizobia like bacteria were isolated and were investigated for their specific PGP traits, production of hydrolytic enzymes. Results revealed, four isolates synthesize IAA (22.3 ± 1.45 to 88.6 ± 1.45 μg mL−1), three isolates solubilized phosphate (40.69 ± 1.25 to 216.3 ± 1.31 μg mL−1), three isolates solubilized potassium, produced siderophore, and showed chitinase production, two isolates possess ACC deaminase activity, one isolate was able to solubilize zinc, 5 isolates produced β- 1, 3-glucanase (0.38 ± 0.005 to 2.82 ± 0.011 % units) and four isolates produced cellulase. Two bacterial isolates found to exhibit most of the PGP activities, were selected and identified on the basis of phenotypic, biochemical tests and 16S rRNA sequencing, as Rhizobium tropici IHTF-1 and Rhizobium mayense IHTF-2. Interaction of these potential rhizobium strains individually and consortia with common bean plants under greenhouse conditions boosted root and shoot length, fresh and dry biomass compared to un-inoculated control plants. SEM study revealed that both the strains, IHTF-1 and IHTF-2 colonized common bean roots. These results imply that Rhizobium spp., identified in this work, can be used as bio-inoculants to increase common bean plant production in a sustainable way.