Growth of the yeast Saccharomyces cerevisiae on a non-fermentable substrate: control of energetic yield by the amount of mitochondria

The purpose of this study was to investigate the long-term control of ATP s ynthesis during the course of Saccharomyces cerevisiae batch grown on lacta te, a purely respiratory substrate. For this, we used a respirometric and o n-line calorimetric approach to analyse the energetic balances and the cont rol of energetic metabolism during growth. Enthalpic growth yields assessed by enthalpy balance (taking account of substrate consumption, by-product a ccumulation, biomass formation and heat dissipation) remained constant duri ng the entire exponential growth. Moreover, at the same time, a parallel de crease in basal respiratory rate and enthalpy flux occurred. It is shown th at the decrease in respiration corresponds to a decrease in the amount of m itochondria per cell but not to a change of steady state of oxidative phosp horylation. Taking into account the part of energy used for maintenance, it can be concluded that mitochondria by themselves are the major heat dissip ative system in a fully aerobic metabolism, and that the decrease in the am ount of mitochondria when growth rate decreases leads to an enthalpic growt h yield constant. (C) 2000 Elsevier Science B.V. All rights reserved.