Biochemical characterization and metabolic diversity of soybean rhizobia isolated from Malwa region of Central India

Soybean cultivation in many zones of India shows occurrence of native rhizobia besides other exotically adapted strains. In the current study, 22 rhizobial isolates (recovered from 12 different soybean growing sites) and 8 reference strains were selected for biochemical and metabolic characterization. Of 22 isolates, 18 were recovered as fast growing isolates while the rest were slow growing based on bromothymol blue (BTB) test. Unlike earlier belief that rhizobia have no ability to grow on glucose peptone agar medium, in this study, some isolates and some reference strains grew well on this medium. Similarly, when all the isolates were subjected to ketolactose test, some of the isolates were found to show growth on the medium. In contrast, based on C-utilization pattern (15 carbohydrates) a remarkable metabolic diversity was observed among the rhizobial isolates recovered in the study. The clustering and matching analysis showed that most of isolates were matching with slow growing reference strains, a few were with fast growing reference strains and some were found to be unique and hence not matching with any of reference strains. Such analysis suggests the occurrence of metabolically distinct types of rhizobia besides commonly known types (B. japonicum, B. elkanii and S. fredii) of soybean rhizobia and further validation is suggested through 16SrRNA gene sequencing technique.