Influence of culture and environmental conditions on the composition of exopolysaccharide produced by Agrobacterium radiobacter

Exopolysaccharides (EPS) are produced by many genera of bacteria. These EPS have properties such as high viscosity, stabilizing and emusifying capabilites which make them attractive to the food industry. A strain of Agrobacterium radiobacter was isolated from lettuce which expressed a water-soluble acidic EPS, and a study of its properties was undertaken. EPS production was monitored using a dye binding assay with alcian blue, and concentration was expressed in xanthan equivalents (XE). Maximum production of EPS in mineral salts medium (MSM) occured after 3 days of growth at 28 °C. Both the lettuce isolate (FRP 695) and A. radiobacter ATTCC 6466 (designated FRP 718) produced EPS composed mainly of glucose and galactose. When grown with yeast extract (YE), however, both strains produced EPS containing mannose. The mannose content of the EPS was proportional to YE concentration up to 0.35%, but the yield of EPS was not significantly (P>0.05) influenced by YE. In seed medium containing both YE and peptone, neither the inoculum level (0.25–5.0%) nor pH (5.5–8.0) nor sucrose concentration (0.25–10%) had any significant (P>0.05) effect on the EPS yield. The mannose content was influenced by decreasing sucrose in seed medium, with a maximum of 78% and a minimum of 28% at 0.25 and 7.5% sucrose, respectively. Over all experiment conditions (n=50), mannose content only exceeded 25% (% dry weight) in seed medium; mannose content was ≤23% when the basal medium was MSM. The results suggest that useful changes in composition of EPS can be made through manipulation of the growth environment.