INFLUENCE OF GROWTH-CONDITIONS ON PRODUCTION OF CAPSULAR AND EXTRACELLULAR POLYSACCHARIDES BY RHIZOBIUM-LEGUMINOSARUM

The influence of growth rate and medium composition on exopolymer prod uction by Rhizobium leguminosarum was studied. When grown in medium co ntaining 10 g/l mannitol and 1 g/l glutamic acid, Rhizobium leguminosa rum biovar trifolii TA-1 synthesized up to 2.0 g/l of extracellular po lysaccharide (EPS), and up to 1.6 g/l of capsular polysaccharide (CPS) . Under non-growing cell conditions in medium without glutamic acid, C PS synthesis by strain TA-1 could proceed to 2.1 g/l, while FPS-produc tion remained relatively low (0.8 g/l). Maximal CPS-yield was 2.9 g CP S/l medium in a medium containing 20 g/l mannitol and 2 g/l glutamic a cid. The EPS-deficient strain R. leguminosarum RBL5515.exo4::Tn5 was a ble to produce CPS to similar levels as strain TA-1, but CPS-recovery was easier because of the low viscosity of the medium and growth of th e cells in pellets. With strain TA-1 in nitrogen-limited continuous cu ltures with a constant biomass of 500 mg cell protein/l, EPS was the m ost abundant polysaccharide present at every dilution rate D (between 0.12 and 0.02 h-1) The production rates were 50-100 mg/g protein/h for EPS and 15-20 mg/g protein/h for CPS. Only low amounts of cyclic beta -(1,2)-glucans were excreted (10-30 mg/1) over the entire range of gro wth rates.