Production of extracellular polysaccharides by a Rhizobium species from root nodules of Cajanus cajan

The ability of the Rhizobium sp., isolated from the root nodules of the leg uminous pulse yielding shrub Cajanus cajan, to produce extracellular polysa cccharides (EPS) was checked. A large amount of EPS (1,128 mu g/ml) was pro duced by the bacteria in yeast extract mannitol medium. Growth and EPS prod uction started simultaneously, but the production reached its maximum level in the stationary phase of growth at 28 h. The EPS production by this Rhiz obium sp. was much higher than by many other strains from nodules of Cajanu s cajan which took a much longer time to reach maximum EPS production than this strain. The maximum EPS production (2,561 mu g/ml) was obtained when t he medium was supplemented with mannitol (1%), cetyl pyridinium chloride (2 mu g/ml) and KNO3 (0.2%), in which the production was increased by 276% co mpared to the control. The EPS production rose in the period up to 65 h wit h increased mannitol concentration. The EPS contained arabinose, xylose and rhamnose monomers. The possible role of rhizobial EPS production in root n odule symbiosis is discussed.