Exocellular Succinoglucan Production by Agrobacterium radiobacter NCIB 11883

Abstract

SUMMARY: The efficiency of growth and exopolysacharide production by Agrobacterium radiobacter NCIB 11883 was examined in both carbon- and nitrogen-limited chemostat cultures. Under carbon limitation this organism exhibited two distinct Y maxO2 values, one below D = 0·15 h-1 (40 g mol-1) and the other above this dilution rate (84 g mol-1). Under nitrogen limitation optimum exopolysaccharide production occurred at low dilution rates and under these conditions accounted for virtually all the product carbon excreted. The maximum observed yield of exopolysaccharide was 3·5 g (g O2)-1 and 0·65 g (g glucose)-1. These observed yields when corrected for the cellular requirement for glucose and oxygen gave values very similar to the theoretical value if the ATP/O quotient of carbon-limited cultures grown at corresponding dilution rates was used. Thus, the efficiency of growth of both carbon- and nitrogen-limited cultures was similar once an allowance for exopolysaccharide production was made. Under conditions optimum for polysaccharide production virtually all the respiratory activity occurring over and above that required for growth was utilized in polysaccharide production. Exopolysaccharide production is a major event in energetic terms and the rate of ATP utilization for its synthesis can be equivalent to 90% of that required for cell production. Nevertheless, because of the relationship between the structure of the polysaccharide and the ATP/O quotient extant in A. radiobacter succinoglucan production supplies up to approximately 56% of its own ATP demand during the synthesis of the acid moieties that comprise this polymer.