Presumptive correlation between phenotypic, genotypic and symbiotic diversities with antibiotic susceptibility traits of rhizobial strains from plant legumes

This investigation was carried out to study the extremely diversified characteristics of rhizobial strains isolated from locally produced legumes of different varieties. The rhizobial isolates designated as S 1, S 2, S 3, S 4, S 5 and S 6 were purified and subjected to various morphological, cultural, antibiogram and biochemical and plasmid profiling to unmask their diversified nature to some extent. The study revealed that the Sesbania strain (S 2) possessed extraordinary properties for most other strains. Though the strain is allocated in the slow-growing group, it showed an atypical fast growth rate, and also it produced a profuse amount of exopolysaccharide (EPS)/ lipopolysaccharide (LPS). The Arachis and Vigna strains also showed a faster growth rate than usual, whereas the rate of EPS/LPS production was profuse in the cases of Vigna and Lens strains. This rate was noted low in cases of Pisum and Arachis strains, while Phaseolus produced a moderate amount of EPS/LPS. Like Sesbania, the Pisum strain also absorbed Congo red dye strongly and including Sesbania, all the other strains ware catalase-negative, which was an unusual property of rhizobial strains. Antibiogram profile of the test strains was done to retain experimental strains after plant infection test, as overlapping host range is a common phenomenon in symbiosis. The antibiogram profiles showed that more or less all the strains were resistant to Ampicillin, Bacitracin, and Amoxicillin. Phaseolus strain was intermediate to Bacitracin, and Pisum strain was susceptible to Ampicillin, which can be related to loss of the plasmid. In plasmid profiling of the strains, several numbers of plasmid DNA band was observed under UV transilluminator after gel electrophoresis. In the present study, rhizobial species from different leguminous plants were detected, and plasmids were cured of the cell using acridine orange to determine their effect on Rhizobium spp. for antibiotic resistance. The findings of the research point out the diverse nature of rhizobial isolates with specific reference to the strains infective on Sesbania aculeate, which poses problems to characterize strains infective of different legumes.