Effect of dilution rate and growth-limiting substrate on the metabolic activity of Torula utilis cultures.

SUMMARY: Torula utilis was grown in a chemostat, at several dilution rates, in media containing growth-limiting concentrations of glucose, xylose and ethanol; it was similarly grown in an NH4 +-limited medium (carbon source, glucose). The ‘steady state’ rates of oxygen uptake of cultures, and Q O2 values for washed suspensions of organisms separated from the cultures and incubated with each substrate, were determined at each dilution rate. Differences in oxidation rates indicated quantitative changes in the ‘constitutive’ enzyme content of organisms, which varied according to the growth rate and/or the nature of the growth-limiting substrate. The significance of these changes in terms of metabolic regulation and economy of enzyme synthesis is discussed.