Rhizobial Strains Research Articles

USING SALT-TOLERANT RHIZOBIA TO IMPROVE THE SOYBEAN (GLYCINE MAX) RESILIENCE TO SALINITY

Soybean (Glycine max [L.] Merr.) is an economically important oilseed crop with an annual increase in growing grain demand. Soybean is a moderately salt-tolerant crop; however, salt stress conditions can affect its growth and yield-related traits and, eventually, reduce productivity. In saline soils, one of the techniques to increase soybean productivity is to use rhizobia inoculation. Although, using industrial rhizobia-based biofertilizers is often ineffective due to their lack of adaptability to salinity. Injecting soybeans with salt-tolerant and growth-promoting rhizobia helps mitigate the effects of salt stress harmful to crop plants. The recent study sought to isolate local strains of salt-tolerant rhizobia, studying its ability to increase soybean tolerance to salt stress conditions. Twenty-four local salttolerant rhizobium isolates underwent isolation from root nodules of soybean grown on saline soils. Studying their basic morphological and biochemical characteristics and ability to withstand salt stress led to the final selection of five salt-tolerant strains. The rhizobium strains were able to synthesize metabolites that stimulate growth and help reduce salt stress in plants. The study of rhizobia nodulation ability under saline conditions resulted in selecting the three most efficient strains from the Bradyrhizobium japonicum species. Inoculation of soybean seeds with salt-tolerant rhizobia proved to mitigate the adverse effects of salinity on plant growth by increasing the root size and the number of nodules in the roots. Thus, the study establishes that inoculation of soybean seeds with local salttolerant rhizobia enhances soybean tolerance to salt stress and improves crop growth and adaptation to soil salinity. Using isolated local strains of salt-tolerant rhizobia will help provide a key and environmentally friendly approach to solving the problem of salt stress for sustainable agriculture.

Complete Genome Sequences of Rhizobium leguminosarum bv. phaseoli BT01, Rhizobium sp. Strain BT03, and Rhizobium sp. Strain BT04, Isolated from Black Turtle Bean Nodules in Ontario, Canada.

We report the complete genome sequences of three Rhizobium strains isolated from nodules of heritage black turtle bean (Phaseolus vulgaris) plants grown in a community garden in Ontario, Canada. The genomes are between 6.91 Mb and 7.98 Mb long and consist of five to seven DNA replicons.

Rhizobial benefits to an herbaceous invader depend on context and symbiotic strain

Background and aimsFor invasive plant species that associate with mutualistic symbionts, partner quality can be critical to their invasion success. This might be particularly true for legumes that host nitrogen-fixing bacteria (rhizobia). Here, we examined the relative effectiveness of rhizobial strains on the invasive legume Lupinus polyphyllus.MethodsWe isolated rhizobia from field populations of L. polyphyllus and conducted inoculation experiments in which we quantified plant growth in greenhouse and common-garden conditions.ResultsDifferences in nodulation and effectiveness in terms of increasing plant growth among rhizobial strains of the genus Bradyrhizobium were more pronounced in the greenhouse than in the common garden. All six rhizobial strains nodulated the host plant in greenhouse conditions, but one failed to nodulate in the common garden. Under greenhouse conditions, five rhizobial strains increased plant biomass by 66–110%, while one provided negligible benefits compared to control plants without rhizobia, suggesting that rhizobial identity might be critical to the invader’s performance. However, the common-garden experiment revealed no differences in the effectiveness of rhizobial strains in terms of plant biomass, number of leaflets per leaf, height, root:shoot ratio, or survival. Moreover, the performance of rhizobia-inoculated plants in the common garden did not differ from plants without rhizobia, which may call into question the fitness benefits of rhizobia to field populations of this species.ConclusionsThe discrepancies observed between the two environments highlight the importance of considering field-realistic growing conditions and multiple plant traits when assessing the potential growth benefits of symbiotic partners to host plants.

Effectiveness of indigenous Rhizobium sp. isolates from peatland soils on soybean (Glycine max L. Merril) growth and production

The low productivity of soybeans can be overcome by cultivating them on peatlands, accompanied by the provision of indigenous Rhizobium strains derived from peatlands. Isolating Rhizobium sp. from peatlands is believed to enhance soybean productivity on such land. This study aims to determine the effectiveness of local Riau Rhizobium sp. isolates for soybean cultivation in Riau peatlands. Six isolates of Rhizobium sp. were used in this study, obtained from plants growing on peatlands: IIMB4, IIRM1, IIRM2 from the rhizosphere of Mucuna bracteata, and IIRA4, IIRA2, IIRA6 from the rhizosphere of Acacia crassicarpa. The experiment followed a completely randomized design (CRD), with each treatment replicated four times. The treatments included control, commercial Rhizobium sp., isolates IIMB4, IIRA2, IIRA6, IIRM2, IIRA4, and IIRM1. The results demonstrated that all indigenous Rhizobium sp. isolates from peatlands, particularly IIMB4, effectively formed symbiotic associations with soybean plant roots, improving growth parameters and increasing soybean production. Nevertheless, it is also necessary to assess the effectiveness of these Rhizobium sp. isolates on various other leguminous plant species to identify the most efficient symbiotic isolates across different leguminous crops.

Molecular Characterization of Indigenous Rhizobia from Kenyan Soils Nodulating with Common Beans.

Kenya is the seventh most prominent producer of common beans globally and the second leading producer in East Africa. However, the annual national productivity is low due to insufficient quantities of vital nutrients and nitrogen in the soils. Rhizobia are symbiotic bacteria that fix nitrogen through their interaction with leguminous plants. Nevertheless, inoculating beans with commercial rhizobia inoculants results in sparse nodulation and low nitrogen supply to the host plants because these strains are poorly adapted to the local soils. Several studies describe native rhizobia with much better symbiotic capabilities than commercial strains, but only a few have conducted field studies. This study aimed to test the competence of new rhizobia strains that we isolated from Western Kenya soils and for which the symbiotic efficiency was successfully determined in greenhouse experiments. Furthermore, we present and analyze the whole-genome sequence for a promising candidate for agricultural application, which has high nitrogen fixation features and promotes common bean yields in field studies. Plants inoculated with the rhizobial isolate S3 or with a consortium of local isolates (COMB), including S3, produced a significantly higher number of seeds and seed dry weight when compared to uninoculated control plants at two study sites. The performance of plants inoculated with commercial isolate CIAT899 was not significantly different from uninoculated plants (p > 0.05), indicating tight competition from native rhizobia for nodule occupancy. Pangenome analysis and the overall genome-related indices showed that S3 is a member of R. phaseoli. However, synteny analysis revealed significant differences in the gene order, orientation, and copy numbers between S3 and the reference R. phaseoli. Isolate S3 is phylogenomically similar to R. phaseoli. However, it has undergone significant genome rearrangements (global mutagenesis) to adapt to harsh conditions in Kenyan soils. Its high nitrogen fixation ability shows optimal adaptation to Kenyan soils, and the strain can potentially replace nitrogenous fertilizer application. We recommend that extensive fieldwork in other parts of the country over a period of five years be performed on S3 to check on how the yield changes with varying whether conditions.

Multitask Approach to Localize Rhizobial Type Three Secretion System Effector Proteins Inside Eukaryotic Cells.

Rhizobia can establish mutually beneficial interactions with legume plants by colonizing their roots to induce the formation of a specialized structure known as a nodule, inside of which the bacteria are able to fix atmospheric nitrogen. It is well established that the compatibility of such interactions is mainly determined by the bacterial recognition of flavonoids secreted by the plants, which in response to these flavonoids trigger the synthesis of the bacterial Nod factors that drive the nodulation process. Additionally, other bacterial signals are involved in the recognition and the efficiency of this interaction, such as extracellular polysaccharides or some secreted proteins. Some rhizobial strains inject proteins through the type III secretion system to the cytosol of legume root cells during the nodulation process. Such proteins, called type III-secreted effectors (T3E), exert their function in the host cell and are involved, among other tasks, in the attenuation of host defense responses to facilitate the infection, contributing to the specificity of the process. One of the main challenges of studying rhizobial T3E is the inherent difficulty in localizing them in vivo in the different subcellular compartments within their host cells, since in addition to their low concentration under physiological conditions, it is not always known when or where they are being produced and secreted. In this paper, we use a well-known rhizobial T3E, named NopL, to illustrate by a multitask approach where it localizes in heterologous hosts models, such as tobacco plant leaf cells, and also for the first time in transfected and/or Salmonella-infected animal cells. The consistency of our results serves as an example to study the location inside eukaryotic cells of effectors in distinct hosts with different handling techniques that can be used in almost every research laboratory.

Effect of cultivar and inoculant on yields of faba beans (Vicia faba minor) and subsequent spring wheat (Triticum aestivum) under Scandinavian cropping conditions

Inoculation of legumes is generally considered to increase yield and to lower the need of nitrogen (N) fertilization, especially in semiarid regions and on sandy soils. It has not been clear whether inoculation with Rhizobium sp. in cropping of faba beans (Vicia faba minor) under Swedish conditions would improve yield and protein content. In 2015–2016, three faba bean cultivars and two strains of Rhizobium were studied in field trials in Central Sweden, including analyses of N fixation capacities using 15N abundance. The study did not show any effects of inoculation of Rhizobium on yield or protein content of faba beans or subsequent spring wheat yields. Yields of faba beans varied between cultivars but were not connected to inoculation. 15N abundance was influenced by rhizobium. The study cannot support the opinion that, generally, inoculation is beneficial for improved outcome of faba bean cropping under Scandinavian field conditions. No residual effect of inoculation on subsequent spring wheat yield was found.

Genetic diversity, symbiotic efficiency, stress tolerance, and plant growth promotion traits of rhizobia nodulating Vachellia tortilis subsp. raddiana growing in dryland soils in southern Morocco

In the present study, we analyzed the genetic diversity, phylogenetic relationships, stress tolerance, phytobeneficial traits, and symbiotic characteristics of rhizobial strains isolated from root nodules of Vachellia tortilis subsp. raddiana grown in soils collected in the extreme Southwest of the Anti-Atlas Mountains in Morocco. Subsequent to Rep-PCR fingerprinting, 16S rDNA gene sequencing of 15 representative strains showed that all of them belong to the genus Ensifer. Phylogenetic analysis and concatenation of the housekeeping genes gyrB, rpoB, recA, and dnaK revealed that the entire collection (except strain LMR678) shared 99.08 % to 99.92% similarity with Ensifer sp. USDA 257 and 96.92% to 98.79% with Sinorhizobium BJ1. Phylogenetic analysis of nodC and nodA sequences showed that all strains but one (LMR678) formed a phylogenetic group with the type strain “E. aridi” LMR001T (similarity over 98%). Moreover, it was relevant that most strains belong to the symbiovar vachelliae. In vitro tests revealed that five strains produced IAA, four solubilized inorganic phosphate, and one produced siderophores. All strains showed tolerance to NaCl concentrations ranging from 2 to 12% and grew at up to 10% of PEG6000. A greenhouse plant inoculation test conducted during five months demonstrated that most rhizobial strains were infective and efficient. Strains LMR688, LMR692, and LMR687 exhibited high relative symbiotic efficiency values (respectively 231.6 %, 171.96 %, and 140.84 %). These strains could be considered as the most suitable candidates for inoculation of V. t. subsp. raddiana, to be used as a pioneer plant for restoring arid soils threatened with desertification.

The Genome of a Pigeonpea Compatible Rhizobial Strain '10ap3' Appears to Lack Common Nodulation Genes.

The symbiotic fixation of atmospheric nitrogen (N) in root nodules of tropical legumes such as pigeonpea (Cajanus cajan) is a complex process, which is regulated by multiple genetic factors at the host plant genotype microsymbiont interface. The process involves multiple genes with various modes of action and is accomplished only when both organisms are compatible. Therefore, it is necessary to develop tools for the genetic manipulation of the host or bacterium towards improving N fixation. In this study, we sequenced the genome of a robust rhizobial strain, Rhizobium tropici '10ap3' that was compatible with pigeonpea, and we determined its genome size. The genome consisted of a large circular chromosome (6,297,373 bp) and contained 6013 genes of which 99.13% were coding sequences. However only 5833 of the genes were associated with proteins that could be assigned to specific functions. The genes for nitrogen, phosphorus and iron metabolism, stress response and the adenosine monophosphate nucleoside for purine conversion were present in the genome. However, the genome contained no common nod genes, suggesting that an alternative pathway involving a purine derivative was involved in the symbiotic association with pigeonpea.

Strategies for Improving Cowpea Grain Yield in the Eastern Amazon: Biological Nitrogen Fixation, Phosphorus Nutrition, and Molybdenum Seed Enrichment

ABSTRACT This work aimed to evaluate the use of phosphorus (P) fertilizer, rhizobia inoculation, and seed enrichment with molybdenum (Mo) as tools for enhancing the cowpea yield in the Brazilian eastern Amazon. A set of field and greenhouse experiments were carried out in cerrado and upland forest environments. Four levels of P fertilization, eight rhizobia strains, and the application of mineral nitrogen (N) were evaluated for the cultivar BRS Tumucumaque (BR = Brasil e S = Sementes), and two levels of Mo seed enrichment were assessed for the cultivars BRS Tumucumaque and BRS Guariba. Grain yield increased linearly with the level of P applied. Inoculation with the rhizobia strain BR 3267 increased the shoot and nodule mass of the cultivar BRS Tumucumaque. There was no difference in grain yield and grain N accumulation between inoculation with seven rhizobia strains, N mineral fertilization and the control (without inoculation and N fertilization) in cerrado and upland forest environments. Cowpea grain yield and grain N accumulation were higher in the cerrado than in the upland forest environment and when the seeds were enriched with Mo. Phosphorus fertilization and seed enrichment with Mo are efficient tools to enhance cowpea yield in the Brazilian Amazon.

Comparative genome analysis of Sesbania cannabina-nodulating Rhizobium spp. revealing the symbiotic and transferrable characteristics of symbiosis plasmids.

Symbiotic nitrogen fixation between legumes and rhizobia makes a great contribution to the terrestrial ecosystem. The successful symbiosis between the partners mainly depends on the nod and nif genes in rhizobia, while the specific symbiosis is mainly determined by the structure of Nod factors and the corresponding secretion systems (type III secretion system; T3SS), etc. These symbiosis genes are usually located on symbiotic plasmids or a chromosomal symbiotic island, both could be transferred interspecies. In our previous studies, Sesbania cannabina-nodulating rhizobia across the world were classified into 16 species of four genera and all the strains, especially those of Rhizobium spp., harboured extraordinarily highly conserved symbiosis genes, suggesting that horizontal transfer of symbiosis genes might have happened among them. In order to learn the genomic basis of diversification of rhizobia under the selection of host specificity, we performed this study to compare the complete genome sequences of four Rhizobium strains associated with S. cannabina, YTUBH007, YTUZZ027, YTUHZ044 and YTUHZ045. Their complete genomes were sequenced and assembled at the replicon level. Each strain represents a different species according to the average nucleotide identity (ANI) values calculated using the whole-genome sequences; furthermore, except for YTUBH007, which was classified as Rhizobium binae, the remaining three strains were identified as new candidate species. A single symbiotic plasmid sized 345-402 kb containing complete nod, nif, fix, T3SS and conjugal transfer genes was detected in each strain. The high ANI and amino acid identity (AAI) values, as well as the close phylogenetic relationships among the entire symbiotic plasmid sequences, indicate that they have the same origin and the entire plasmid has been transferred among different Rhizobium species. These results indicate that S. cannabina stringently selects a certain symbiosis gene background of the rhizobia for nodulation, which might have forced the symbiosis genes to transfer from some introduced rhizobia to the related native or local-condition-adapted bacteria. The existence of almost complete conjugal transfer related elements, but not the gene virD, indicated that the self-transfer of the symbiotic plasmid in these rhizobial strains may be realized via a virD-independent pathway or through another unidentified gene. This study provides insight for the better understanding of high-frequency symbiotic plasmid transfer, host-specific nodulation and the host shift for rhizobia.

PHENOTYPIC AND GENETIC DIVERSITY OF NATIVE RHIZOBIUM ISOLATED FROM ROOT NODULES OF LEGUMINOUS PLANTS GROWN IN RECLAIMED SOIL, EGYPT

An investigation of the phenotypic characteristics of 19 rhizobial strains, isolated from root nodules of different plant legumes grown in the soil of agriculture farms in Ismailia governorate, transpired. Most isolates were creamy or white opaque, mucoid, with a convex elevation, translucent, and smooth margined. Microscopic investigation revealed that all bacterial isolates were rod-shaped and had no positive affinity for Gram-stain. Identifying rhizobial cultures from any bacterial contaminants employed confirmatory tests based on prepared special media, including YMA supplement with Congo red, glucose peptone agar, Kit-lactose agar, and Hoffer’s alkaline test. Based on an infectivity test, all isolates proved their ability to reinfect their host. These rhizobial isolates, classified into two categories, included fast and slow-growing rhizobia according to their growth in the YEM medium containing bromothymol blue (BTB). Meanwhile, the assessment of the genetic diversity among these isolates proceeded using ISSR and RAPD markers, which ISSR marker proved a more powerful tool in discriminating among the tested isolates than the RAPD marker. The cluster analysis, with the RAPD marker, classified the isolates into two main groups. The first group included the isolates (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 13), while the second group contained the isolates (12, 14, 15, 16, 17, 18, and 19). Moreover, using ISSR markers also showed a cluster of two main groups with diverse categories; the first cluster included isolates 1 to 11, and the second group contained isolates 12 to 19.

Rhizobacteria control damping-off and promote growth of lima bean with and without co-inoculation with Rhizobium tropici CIAT899.

Rhizoctonia solani compromises the production of lima bean, an alternative and low-input food source in many tropical regions. Inoculation of bacterial strains has been used, but research on their biocontrol and growth promotion potential on lima bean is scarce. The objective of this study was to evaluate the effects of inoculation with rhizobacterial strains of the genera Bacillus, Brevibacillus, Paenibacillus, Burkholderia, Pseudomonas, and Rhizobium in combination or not with N2-fixing Rhizobium tropici on the control of damping-off disease and growth promotion in lima bean plants. Greenhouse experiments were conducted to evaluate the inoculation with bacterial strains with biocontrol potential in combination or not with R. tropici in substrate infected with R. solani CML 1846. Growth promotion of these strains was also assessed. Strains of Brevibacillus (UFLA 02-286), Pseudomonas (UFLA 02-281 and UFLA 04-885), Rhizobium (UFLA 04-195), and Burkholderia (UFLA 04-227) co-inoculated with the strain CIAT 899 (Rhizobium tropici) were the most effective in controlling R. solani, reducing the disease incidence in 47-60% on lima bean. The promising strains used in the biocontrol assays were also responsive in promoting growth of lima bean under disease and sterile conditions. A positive synergistic effect of co-inoculation of different genera contributed to plant growth, and these outcomes are important first steps to improve lima bean production.

Evaluation of Rhizobium strains collected in Tungurahua and Cotopaxi on the growth of Lupinus mutabilis, under semi-controlled conditions

Evaluation of Rhizobium strains collected in Tungurahua and Cotopaxi on the growth of Lupinus mutabilis, under semi-controlled conditions

Application of Municipal Solid Waste Compost and Green Manure Exerted Residual Effects on Soil Nutrient Content and Plant Nutrient Uptake in Rice

Aims: Rice is the most widely consumed staple food as well as Bangladesh. With the global upsurge in population, rapid urbanization, and industrialization increasing waste production in urban areas and managing them becoming a major concern. Municipal solid waste (MSW) is considered an important recycling tool for use in agricultural fields as compost. Green manure (GM) is another thing thatprovides a substantial portion of the nitrogen requirement of rice. Both MSW compost and GM add organic matter to the soil. We conducted a study to know the residual effects of municipal solid waste (MSW) compost and green manure (GM) on nutrient contents in soil and uptakes in rice (BINA Dhan-7).
 Methods: The experiment was conducted with a Randomized Complete Block Design (RCBD), nine treatments, and three replications. The present rice crop received no fertilizers during the cultivation period. MSW compost and GM inoculated with Rhizobium strains were incorporated as per treatments in 2 cycles of the Mungbean- Dhaincha- Rice cropping pattern.
 Results: The highest nutrient content and uptake were recorded with higher rates of MSW compost and GM application in the preceding crops. Compost is a slow-release source of nitrogen and most nitrogen remaining after completion of the composting process is bound into organic forms. After application nutrients do not become available immediately for plant uptake, and remain as residue which contributes to improving soil quality for several years after application ceases. MSW compost and GM increases soil nutrient contents, availability, and uptake by adding organic matter, increasing the C: N ratio, and soil’s physical, chemical, and biological properties.
 Conclusion: The MSW compost and GM can provide a significant amount of residual effects on the nutrient content in the soil and uptake in rice which depends on the nutrient composition of applied manure in previous crops.

Selected indigenous drought tolerant rhizobium strains as promising biostimulants for common bean in Northern Spain.

Drought is the most detrimental abiotic stress in agriculture, limiting crop growth and yield and, currently, its risk is increasing due to climate change. Thereby, ensuring food security will be one of the greatest challenges of the agriculture in the nearest future, accordingly it is essential to look for sustainable strategies to cope the negative impact of drought on crops. Inoculation of pulses with biostimulants such as rhizobium strains with high nitrogen fixation efficiency and drought-tolerance, has emerged as a promising and sustainable production strategy. However, some commercial inoculums are not effective under field conditions due to its lower effectiveness against indigenous rhizobium strains in the establishment of the symbiosis. Thus, in the present study, we evaluated the ability to improve drought tolerance in common bean plants of different indigenous rhizobia strains isolated from nearby crop fields in the Basque Country either affected by drought or salinity. The plants in this trial were grown in a climatic chamber under controlled conditions and exposed to values of 30% relative soil water content at the time of harvest, which is considered a severe drought. From the nine bacteria strains evaluated, three were found to be highly efficient under drought (namely 353, A12 and A13). These strains sustained high infectiveness (nodulation capacity) and effectiveness (shoot biomass production) under drought, even surpassing the plants inoculated with the CIAT899 reference strain, as well as the chemically N-fertilized plants. The tolerance mechanisms developed by plants inoculated with 353, A12 and A13 strains were a better adjustment of the cell wall elasticity that prevents mechanical damages in the plasma membrane, a higher WUE and an avoidance of the phenological delay caused by drought, developing a greater number of flowers. These results provide the basis for the development of efficient common bean inoculants able to increase the yield of this crop under drought conditions in the Northern Spain and, thus, to be used as biostimulants. In addition, the use of these efficient nitrogen fixation bacteria strains is a sustainable alternative to chemical fertilization, reducing cost and minimizing its negative impact on environment.

A simple method for creating transgenic pea hairy roots using a Japanese pea cultivar and a Japanese Rhizobium radiobacter strain.

Pea (Pisum sativum) is an agriculturally important leguminous crop cultivated worldwide. It is also the plant from which phytoalexin was isolated for the first time. Several studies have investigated gene functions using pea hairy root culture systems. However, the procedures for producing hairy roots are relatively complicated and only a few pea cultivars and Rhizobium strains have been used. In this study, we established a simple method for generating transgenic hairy roots using a pea cultivar and a Rhizobium strain available in Japan. The transformation efficiency for the transgenic hairy roots (approximately 14%) was calculated on the basis of GFP fluorescence because the binary vector used in this study carried a GFP cassette as a marker. Furthermore, we confirmed that the production of the phytoalexin (+)-pisatin was induced by a copper dichloride treatment, indicating that this system can be used to characterize the biosynthesis of (+)-pisatin, which is a compound with a unique pterocarpan structure. Interestingly, some of the hairy roots turned into crown galls during the culture period. In summary, our simple method enables the production of transgenic pea hairy roots using biological materials accessible in Japan. The generated hairy roots can be used to elucidate the molecular mechanisms underlying (+)-pisatin biosynthesis as well as hairy root/crown gall formation.

Co-inoculant Response of Microbial Consortia on Physiology of Blackgram [Vigna mungo (L.) Hepper] Seed Germination

Background: Blackgram (Vigna mungo (L.) Hepper) belonging to the Leguminoceae family is rich in protein. In this crop, biological seed treatment is an environmentally sound approach for improving the vigour of seeds. Besides legume-Rhizobium symbiosis, several other beneficial microbes play a crucial role in vigour enhancement in blackgram. Methods: The surface sterilised seeds were first coated with 20% gum acacia followed by the coating with bioinoculants viz., T0 - Control (Dry seed), T1 - Rhizobium sp. BMBS + Arbuscular Mycorrhizal Fungi (AMF) + Methylobacterium extorquens AM1 and T2 - Rhizobium sp. BMBS + AMF + Bacillus velezensis. Result: Inoculation of blackgram seeds with the Rhizobium sp. BMBS and AMF with Methylobacterium extorquens AM1 resulted in a significant increase in germination (97%), dry matter production (0.237 g 10 seedlings-1), vigour index (22.99) and seed mobilization efficiency (1.11) as compared to control seeds. The biochemical parameters such as á-amylase and proteases were found to be significantly higher in the Rhizobium sp. BMBS + AMF + Methylobacterium extorquens AM1 inoculated seeds. Changes in root exudates composition due to co-inoculation assessed through GC-MS, indicated compounds with antioxidant and antimicrobial activities. Our results confirmed that the positive interaction of rhizobial strain BMBS and AMF with Methylobacterium extorquens AM1 may emerge as a novel bio-inoculant for sustainable pulse productivity.

Bradyrhizobium zhengyangense sp. nov., isype strains of the most closely related species ofolated from effective nodules of Arachis hypogaea L. in central China.

Three slow-growing rhizobial strains (WYCCWR 12678, WYCCWR 12774 and WYCCWR 13023T) isolated from effective nodules of Arachis hypogaea L. (cultivated peanut) sampled in Zhengyang County, Henan Province, central China were characterized using a polyphasic approach. The three strains were assigned to the genus Bradyrhizobium based on phylogenetic analysis of their 16S rRNA sequences. Phylogenetic analysis based on their concatenated recA-glnII-gyrB-dnaK-rpoB gene sequences placed the strains into a distinct lineage. Whole-genome average nucleotide identity (ANI) values between WYCCWR 13023T and WYCCWR 12774 and WYCCWR 12678 were 99.43 and 99.31% respectively. ANI values between WYCCWR 13023T and the most closely related strains were all below 93 %. The digital DNA–DNA hybridization (dDDH) values between WYCCWR 13023T and ‘ B. guangzhouense ’ CCBAU 51670T, B. manausense BR 3351T and B. guangdongense CCBAU 51649T, the three most closely related type strains, were 50.40, 43.50 and 39.20% respectively. Phenotypic characterization also allowed the differentiation of the novel strains from their most closely related type strains. Based on the genotypic and phenotypic features, we conclude that the three strains represent a novel species for which the name Bradyrhizobium zhengyangense sp. nov. is proposed, with WYCCWR 13023T (=GDMCC 1.3180T=HAMBI 3760T) as the type strain.

Enhanced degradation of fomesafen by a rhizobial strain Sinorhizobium sp. W16 in symbiotic association with soybean

Fomesafen, a broad-spectrum herbicide with a long duration, is frequently applied in legume farmlands, causing severe damage to crop growth and the local environment. Sinorhizobium sp. W16 was a fomesafen-degrading rhizobium isolated from a soybean nodule. The pure culture assay revealed that strain W16 efficiently degraded 5 mg L−1 of fomesafen by 69 % over 7 days. Three metabolites were identified by liquid chromatography and time-of-flight mass spectrometry, revealing strain W16 was the first strain isolated to catalyze the cleavage of ether bond of fomesafen. The results of the pot experiment demonstrated that strain W16 colonizes the soybean rhizosphere for over 50 days and eliminates the inhibition of fomesafen on nitrogen fixation by increasing the activity of nitrogenase and stimulating the indigenous nitrogen-fixing microbes in the rhizosphere. The symbiotic relationship between strain W16 and legumes promotes soil fomesafen degradation rates by 29.17 %–57.87 %. This study provides valuable information about a novel fomesafen-degrading rhizobium with great potential for promoting the bioremediation of herbicide-contaminated farmland soil due to the development of symbiotic systems with legumes.