The effect of two inhibiting substrates on growth kinetics and cell maintenance of the yeast Candida valida

Abstract

The biomass yield, Y X/S, and the specific growth rate, μ, of the ethanol-utilising yeast Candida valida was studied over a wide range of concentrations of two substrates, ethanol and zinc. The experimental results suggested that the cell maintenance rate, m S, was affected by each. Ethanol at high concentrations exerted substrate inhibition on the culture growth, which was manifested as a decrease of ethanol consumption rate and an increase of m S. A sharp increase of m S was observed at very low and high zinc concentrations, which might be a result of energy expenditure on zinc transport. The dependencies of biomass yield on specific growth rate during the variation of ethanol and zinc concentrations were two-branched, that for ethanol having the shape of a loop. A mathematical model of the cultures has been developed which is in good agreement with the experimental data.