THE INHIBITION OF THE MAXIMUM SPECIFIC GROWTH AND FERMENTATION RATE OF ZYMOMONAS-MOBILIS BY ETHANOL

The inhibition of the maximum specific growth and fermentation rate of Zymomonas mobilis by ethanol was studied in turbidostat cultures at constant and stepwise changed ethanol concentrations. Up to 50 g/L ethanol, the inhibition kinetics can be approximated by a linear relationship between the specific growth rate and the ethanol concentration. Above this level, deviations from this linearity are observed. The specific fermentation rates were less inhibited by ethanol than was the specific growth rate. The maximum ethanol concentration achieved was 72 g/L. The reponse time for the adaptation of a turbidostat culture to step changes in the ethanol concentration was markedly dependent on the concentration level, the response time being larger at high ethanol concentrations.