The extracellular polysaccharide produced by Enterobacter spp. isolated from root nodules of Abrus precatorius L.

Extracellular polysaccharide (EPS) of symbiotic bacteria is indispensible for the invasion of root that leads to formation of nodule in legume plant. The chemical structure of the EPS is important for structural recognition at the early stage of infection in highly host specific legume-bacteria symbiosis. Two bacterial strains A3CK and A7CK isolated from the root nodule of legume Abrus precatorius and identified as Enterobacter spp. based on 16S rDNA sequence homology. Both the strains were found to produce copious amount of EPS (88 and 122 µg/ml respectively) in yeast extract mineral medium. The EPS production was increased 485 µg/ml and 656 µg/ml by A3CK and A7CK strain respectively after the medium supplemented with preferable carbon (mannitol), nitrogen (L-asparagine), and vitamin (B12). Gas chromatography coupled with mass spectrometry (GC–MS) analysis of EPS was performed to determine the presence of sugar monomers. GC–MS analysis of alditol-acetate derivatives of acid hydrolyzed EPS of these two strains revealed that presence of sugars such as mannose, glucose and galactose in A3CK strain, whereas glucose and galactose present in A7CK strain. FT-IR spectrum of the EPS indicated the presence of hydroxyl, methyl and carboxylate groups in both the two strains. The possible role of bacterial EPS production in root nodule and their roles in plant – bacteria interaction are briefly discussed.