The extracellular polysaccharide produced by Rhizobium sp. isolated from the root nodules of Phaseolus mungo

Abstract

The symbiont isolated from root nodules of Phaseolus mungo L., a widely grown legume in India was identified as a Rhizobium sp. a Rhizobium sp. close to R. multihospitium based on a biochemical and 16S rRNA gene-based phylogenetic approach. This Rhizobium sp. was able to produce large amounts of extracellular polysaccharides (EPS) in a yeast extract mannitol (YEM) broth medium. Both growth and EPS production started simultaneously though each had different stationary phases. EPS production increased enormously with supplementation by the preferred carbon, nitrogen and vitamin sources. Attempts were made to optimize the cultural requirements for maximum growth and maximum EPS production. The EPS produced by the symbiont contained large amount of mannose together with small amounts of arabinose and xylose. The possible role of EPS production on the Rhizobium—root nodule symbiosis is briefly discussed.