Kinetics of yeast growth:inhibition-threshold substrate concentrations

Two Candida species and a Saccharomyces were grown on ethyl alcohol, acetic acid, ethyl acetate, and I-butanol, and their growth rates at a series of concentrations of each substrate are reported. Substrate concentrations higher than a characteristic threshold substrate concentration Stheta inhibited growth in accordance with a new relationship: mu = mumaxS/(k+S) - i(S - Stheta, where i is an inhibition constant and the other symbols have their usual meanings. Complete inhibition, that is, no growth, takes place when S = Si, the total inhibition concentration. Values of Stheta, Si, and i were calculated for the examples studied. Also discussed are the observed lag periods and also the lowered yields at high substrate concentrations.