Production and Composition of Extracellular Polysaccharide Synthesized by Rhizobium undicola Isolated from Aquatic Legume, Neptunia oleracea Lour.

Abstract

Symbiont isolated from root nodules of Neptunia oleracea, an aquatic legume, designated as N37. It was identified as a Rhizobium undicola based on phenotypic characterization, 16S rRNA gene-based phylogenetic approach and whole genome relatedness. The R. undicola strain N37 was able to produce a large amount of extracellular polysaccharide in yeast extract mannitol medium. The growth and extracellular polysaccharide production started simultaneously and both had same stationary phases. Attempts were made to optimize the cultural requirements for maximum growth and extracellular polysaccharide production. The production increased enormously (515 µg/ml) with supplementation of preferred carbon, nitrogen and vitamin sources. Gas chromatographic analysis of extracellular polysaccharide isolated from R. undicola strain N37 revealed the presence of galactose (94.17 %) as predominant monomers together with very small amount of mannose (5.83 %). Fourier transformation infrared spectroscopy of extracellular polysaccharide indicated the presence of hydroxyl, methyl and carboxylate groups. The possible role of extracellular polysaccharide production on symbiosis was briefly discussed.