The influence of cultural conditions on polysaccharide production by Aerobacter aerogenes.

Abstract

SUMMARY: The polysaccharide content of Aerobacter aerogenes surface cultures grown on defined media was estimated by the anthrone method and related to the amount of growth as measured by the non-dialysable nitrogen content. Observations after different periods of incubation at 35° showed that on a medium containing excess sugar, growth was complete after 24 hr. and polysaccharide production was complete after 4 days. While most of the polysaccharide was produced after the cessation of growth, the rate of production per cell was greatest in the logarithmic phase. The polysaccharide: nitrogen ratio was low in 4-day cultures on media wherein cessation of growth was due to exhaustion of sugar (the sole carbon and energy source) and also was low in growths limited by anaerobic conditions or by the development of acidity. It was increased 10–20-fold in cultures wherein cessation of growth was due to exhaustion of limited nitrogen, phosphorus or sulphur sources, so that an excess of sugar remained available for extra polysaccharide synthesis. This great increase in the polysaccharide: nitrogen ratio of the culture was paralleled by similar increases in the degree of mucoidness as measured by the wet weight: nitrogen ratio, in the intracellular polysaccharide content as measured by periodate-Schiff staining, in capsular polysaccharide as measured by capsule diameter, and in loose slime polysaccharide as measured chemically in the supernatant after centrifugation of the culture. After 4 days at 35° the loose slime accounted for about half of the total polysaccharide in the highly mucoid cultures and about a fifth of that in the non-mucoid cultures.