Isolation and characterization of an endophytic bacterium, Bacillus megaterium KHDEB4, associated with root-nodules of green gram cv.OUM-11-15 (Vigna radiata L.) and its role in Chromium (VI) tolerance

Abstract

Vigna radiata L. (Green gram) is an important legume crop in India due to its high nutritive value and proteinaceous nature. Soil bacteria exist in root or root-nodules of V. radiata in either symbiotic relationships or in associations. In the current study, the endophytic bacterium Bacillus megateriumstrain KHDEB4 was isolated from surface-sterilized rootnodules of V. radiatacv.OUM-11-15and characterized phenotypically and genotypically. The results indicated that KHDEB4 consumed a variety of sugars as sole carbon source, and produced catalase, amylase, urease but not nitrite as well as nitrate reductase. KHDEB4 exhibited some plant growth-promoting traits, such as production of indole acetic acid and acetoin (in MR VP test). In addition, comparative sequence analysis of the 16S rRNA gene showed that KHDEB4 exhibited 99 % homology with Bacillus megaterium.The 16S rRNA sequence of Bacillus megateriumstrain KHDEB4was submitted to NCBI gene bank and catalogued the accession number as KY679149. Bacillus megateriumstrain KHDEB4 was found to be pH tolerant (up to 8.5) and also could tolerate heavy metal Chromium (VI) in the form of potassium dichromate (K2 Cr2 O7)salt up to concentration of 130ppm. In conclusion, Bacillus megateriumstrain KHDEB4belongs to the group of plant growth promoting rhizobacteria and could have significant applications on Cr (VI) tolerance and its rhizoremediation along with crops.