[Principle growth indices of a chemostat Candida utilis culture resistant to acid pH values]

Abstract

The kinetics of growth of the Candida utilis chemostat culture 1668-3-37 was studied in a synthetic medium with ethanol at different values of pH and temperature. Chemostat curves were obtained for the pH of the medium of 4.5 and 3.0 and the temperature of 32 degrees C. The following growth characteristics were determined: the maximal growth rate (mumax), the economical coefficient (Y), the substrate (saturation) constant (Ks), the rate of ethanol uptake (q), maintenance energy (m). The minimal amount of ethanol inhibiting the yeast growth was assayed in short-term experiments under periodic conditions with shaking. The value of mumax was 0.35 hr-1 when the yeast was cultivated at 32 degrees C and the pH 4.5, and 0.32 hr-1 at the pH 3.0. The value of Ks varied by an order of magnitude at different pH values when the chemostat culture was grown at D=0.2 hr-1: 36.0 mg/litre at the pH of 3.0 and 3.75 mg/litre at the pH of 4.5. The value of m was close to 0 at the pH of 4.5 and equaled 5--7 mg of ethanol per gram of dry biomass per hour at the pH of 3.0; it was still higher when the temperature of cultivation was increased to 38 degrees C. The minimal substrate (ethanol) concentration inhibiting the yeast growth was constant at different cultivation conditions (pH 3.0 or 4.5 and temperature 32 or 38 degrees C), being equal to 0.45% (v/v) of ethanol.