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The symbiotic system of Legumes and root-nodule bacteria is a significant process for enriching barren and dry soils and supporting plant growth. The aim of this study was to isolate root-nodule bacteria from Medicago falcate and to select high activity strains with resistance to environmental stress. As a result, only MSZ-25 strain grew in the medium containing 0.8M NaCl, with pH4.8-9.8 and at temperatures of 4-45°С. All rhizobial isolates were tolerant to the concentrations of 0.01-0.1% Pb(NO3)2, 0.01% ZnSO4, CdCI2, CuCI2 and NiCI2. The strains were also resisted to penicillin 10μ/ml, erythromycin 10μ/ml, and chlorampenicol 10μ/ml but the growths of all isolates were inhibited by kanamycin 30μ/ml, novobiocin 30μ/ml and tetracycline 10μ/ml.

The importance of atmospheric nitrogen-fixing bacteria The study aimed to isolate bacteria from the roots of plants From four areas of the city of Mosul the winter agriculture, season 2020-2021 and using biochemical tests and phenotypic and agricultural characteristics to diagnose bacterial isolates and study sensitivity and resistance of bacterial isolates to ten antibiotics. if the results showed that the highest percentage of resistance was to the two antibiotics, Trimethoprim, and streptomycin, at 100%, while The least resistance was to the two antivirals Gentamycin and Rifampicin by 20%. In addition to Studying The sensitivity and resistance of bacterial isolates to four heavy Metals, namely Mercury chloride (HgCl), Cobalt chloride (CoCl), Cadmium Chloride (CdCl), and nickel chloride (NiCl). The resistance was high with Cadmium chloride salt (CdCl) and the lowest salt Mercury Chloride (HgCl). PCR techniques were used to diagnose samples based on 16S rRNA sequence analysis and comparison of sequences resulting from DNA amplification with standard isolates within NCBI to detect new bacterial isolates

The common rhizobial population in the soil is neither high enough nor effective enough to maximize nodulation and nitrogen fixation. In order to find novel rhizobia with specific characteristics, root nodule bacteria in a symbiotic relation with wildly grown legume species in rangeland areas of Iran were studied, and their biodiversity and phylogenetics were also determined. Bacterial strains were isolated from root nodules of 13 legume species in rangelands of Alborz and Qazvin provinces. Serial dilutions were prepared from root nodules and cultured on the YMA medium. Single colonies were subjected to morphological and biochemical evaluations. Genetic identification and phylogenetic study of 14 isolated strains were done based on the sequences of 16S rRNA, atpD, nodA, and nifH genes. Fourteen identified strains belonged to three families, six genera and nine species. For the first time, Paenibacillus sp. (Tal6), Rhizobium laguerreae (Tal71), Neorhizobium alkalisoli (Krj1 and Ghg71), Rhizobium arenae (Ghg21) and Paenibacillus endophyticus (Ghg31-2) were isolated from root nodules of Onobrychis sativa, Trifolium pratense, Colutea buhsei, Astragalus sp., Glycyrrhiza glabra, and Melilotus sp., respectively. Phylogenetic trees were constructed by the maximum-likelihood method. The findings indicated that the complete host range of root nodule bacterial strains remained to be determined. Thus, the host range of specific nodule-forming bacterial species could be much wider than that proposed previously. Finally, different strains of the same bacterial species isolated from various host plants, demonstrated very diverse characteristics based on the biochemical tests and phylogenetic studies, indicating the possible effects that host plants themselves have on the genome of the bacterial strain. [ABSTRACT FROM AUTHOR]

Root nodule bacteria (RNB) or "rhizobia" are a type of plant growth promoting bacteria, typified by their ability to fix nitrogen for their plant host, fixing nearly 65% of the nitrogen currently utilized in sustainable agricultural production of legume crops and pastures. In this study, we sequenced the genomes of 110 RNB from diverse hosts and biogeographical regions, and undertook a global exploration of all available RNB genera with the aim of identifying novel genetic determinants of symbiotic association and plant growth promotion. Specifically, we performed a subtractive comparative analysis with non-RNB genomes, employed relevant transcriptomic data, and leveraged phylogenetic distribution patterns and sequence signatures based on known precepts of symbiotic- and host-microbe interactions. A total of 184 protein families were delineated, including known factors for nodulation and nitrogen fixation, and candidates with previously unexplored functions, for which a role in host-interaction, -regulation, biocontrol, and more, could be posited. These analyses expand our knowledge of the RNB purview and provide novel targets for strain improvement in the ultimate quest to enhance plant productivity and agricultural sustainability.

A molecular phylogenetic analysis of salt-tolerance-related genes was carried out using complete genome sequencing data available for 26 Sinorhizobium meliloti strains and for 25 bacterial strains belonging to 17 genera. It was revealed that the genes of the first and the second stages of the response to salt stress (aqpZ, trkH, and trkA, and betICBA) have copies of many of the above- indicated genes on pSymA. Data obtained can provide evidence that this replicon, known to be essential for nitrogen fixation rhizobia activity, also has a significant role in the formation of a stress-related gene pool. The closest putative phylogenetic relatives were identified for all 14 tested genes and these are the first insights into the evolutionary pathways for the formation of a stress-related gene pool in root nodule nitrogen-fixing bacteria.

The experiment was conducted during the 2018 season at the research station of the College of Agriculture and Forestry (University of Mosul, Iraq) to investigate the effect of volcanic rock dust (VRD) (0, 125, 250 g m-2) and the fertilizer chelated Iron Fe-EDTA (0, 100, 200 mg L-1) on the bacteria Rhizobium fabae, and the growth and yield of two broad bean (Vicia faba L.) varieties, Histal and Aquadulce. A randomized complete block design was used with three replicates and least significant difference (LSD) to compare means at a significance level of 0.05. Results showed that VRD 250 g m-2 obtained the highest significant mean for the following traits: leaf area index (LAI), number of branches per plant, leaf contents of chlorophyll and total iron, number of effective bacteria nodules per plant, 100-seed weight, plant yield, and percentage of protein in the seeds. On the other hand, 200 mg L-1 Fe-EDTA obtained the highest significant mean of all the traits for both varieties, except for LAI and number of branches per plant. The application of Fe-EDTA per plant had no significant effect on the leaf content of chlorophyll for both varieties and the percentage of protein in the seeds for variety Aquadulce. The interaction of VRD 250 g m-2 with 200 mg L-1 Fe-EDTA achieved the highest significant average for all the traits, except for plant height.

The present study aims to address the problem of chromium (Cr) toxicity by providing important insights into the mechanisms involved in its bioremediation. Among the 22 Rhizobium and Sinorhizobium isolates obtained from Sesbania sesban root nodules, Sinorhizobium sp. SAR1 (JX174035.1) tolerated the maximum Cr concentration (1mM) and hence was used for further studies. The excess secretion of extra polymeric substances, as seen from scanning electron micrographs, could be a probable mechanism of adaptation to the Cr stress. The Energy dispersive X-ray spectroscopy data did not show any peaks of Cr. The biosorption studies done on the isolate gave maximum adsorption capacity as 285.71mg/g. The isotherm studies showed a better fit to Langmuir isotherm. The Weber and Morris plot established that the phenomenon of adsorption was governed by film diffusion mechanism. The FTIR analysis suggested the role of cell wall components and extracellular polymeric substances in Cr adsorption to the biomass of Sinorhizobium. On the basis of these results a compiled mechanism of Cr (VI) adsorption and its biotransformation into Cr (III) by Sinorhizobium sp. SAR1 is explained. This work outlines a comprehensive detail for the exact phenomenon of Cr biotransformation by Sinorhizobium sp. SAR1. These results may further help in developing and enhancing effective bioremediation approaches.

Leguminous tree root nodule nitrogen-fixing bacteria are critical for recuperation of soil C and N cycle processes after disturbance in tropical forests, while other nodule-associated bacteria (NAB) may enhance nodule development and activity, and plant growth. However, little is known of these root nodule microbiomes. Through DNA analysis, we evaluated the bacterial taxa associated with the root nodules of the 1-year-old, 2-year-old, 13-year-old, and old growth Inga punctata trees in a cloud forest. Bradyrhizobium diazoefficiens was the dominant taxon found in all nodules at 63.16% to 85.71% mean percent sequences (MPS) of the total nodule bacterial DNA and was found in the youngest nodules examined (1 year old), suggesting that it is the primary nodular bacteria. There were 26 other NAB genera with collective MPS levels between 7.4% to 12.2%, while 15 of these genera were found in the Bulk Forest soils at collective MPS levels of 4.6%. These bacterial community compositions were different between the NAB and Bulk Forest soils, suggesting the NAB became concentrated within the root nodules, resulting in communities with different compositions from the Bulk Forest soils. Twenty-three of the 26 NAB genera were previously identified with the potential to perform 9 plant growth promoting (PGP) activities, suggesting their importance in root nodule development and plant growth. These NAB communities appeared to successionally develop over time into more complex taxonomic communities, which is consistent with the outcome of advanced microbial communities following succession. The presence of both B. diazoefficiens and the NAB communities in the nodules across all ages of tree roots, and the potential for PGP activities linked with most of the NAB genera, suggest the importance of B. diazoefficiens and the NAB community for nodule development and enhanced development and growth of I. punctata throughout its lifespan, and most critically in the younger plants.

In the present study, a total of 353 nodule-associated bacteria were isolated from 220 legume plant samples belonging to Cicer arietinum (85), Glycine max (74), Vigna radiata (21) and Cajanus cajan (40). A total of 224 bacteria were identified as fast-growing Rhizobium spp. on the basis of differential staining (Gram staining and carbol fuchsin staining) and biochemical tests. All the isolates were tested for indole acetic acid production (IAA), phosphate solubilization and siderophore production on plate assay. To examine the effect of volatile organic metabolites (VOM) and water soluble soil components (WSSC) on nodule bacteria, culture conditions were optimized by observing the effects of various parameters such as pH, salt content and temperatures on the growth of bacteria. Selected rhizobia were subjected to random amplified polymorphic DNA (RAPD) and amplified ribosomal DNA restriction analysis (ARDRA) analysis to identify their species. On the basis of RAPD and ARDRA, 10 isolates were identified as Rhizobium meliloti. In this study, Rhizobium GO4, G16, G20, G77, S43, S81, M07, M37, A15 and A55 were observed as the best candidates among the tested bacteria and can be further used as potent bioinoculants.