PRODUCTION OF EXOPOLYSACCHARIDE FROM LOCAL ISOLATES OF Rhizobium leguminosarum biovar viciae

Fourteen local isolates of Rhizobium leguminosarum biovar viciae were isolated from root nodules of Vicia faba plants collected from agricultural soils of different regions of Nineveh Governorate/Iraq. Six isolates with mucoid colonies were selected as follows: WS14, WS15, WS18, WS21., WS23 and WS26. These local isolates were incubated for periods 1, 2, 3 and 4 days. Dry biomass weight and exopolysaccharide (EPS) (g/L) were recorded. Results revealed that WS18 isolate was the best among the six mentioned isolates of R. leguminosarum biovar viciae , which it gave the maximum production of EPS (6.31 g/L) after two days of incubation. Maximum dry biomass w1.22 g/L after three days of incubation by the same isolate. The effect of addition of different carbon sources to yeast extract mannitol (YEM) broth medium on EPS production by WS18 isolate showed that mannitol, as carbon source was the best for production of EPS (6.36 g/L), after two days of incubation. Two percent was the optimal concentration of mannitol which supported the maximum production of EPS (9.67 g/L) after two days of incubation. The effect of addition of different nitrogen sources at 0.10 % concentration to YEM broth medium (supplement with 2.0 % mannitol) revealed that NaNO 3 gave the best production which reached to 12.94 g/L after two days of incubation. The effective concentration of NaNO 3 support the maximum production was 0.1 %.