METABOLIC RATES DURING SPORULATION OF SACCHAROMYCES-CEREVISIAE ON ACETATE

We have quantified yeast carbon and oxygen consumption fluxes and esti mated anabolic fluxes through glyoxylate and gluconeogenic pathways un der various conditions of sporulation on acetate. The percentage of sp orulation reached a maximum of 55% to 60% after 48 h in sporulation me dium, for cells harvested from logarithmic growth in acetate minimal m edium. When cells were harvested in the stationary phase of growth bef ore transfer to sporulation medium, the maximum percentage of sporulat ion decreased to 40% along with the occurrence of meiosis as could be judged by counting of bi- and tetra-nucleated cells. In both experimen ts, the rates of acetate and oxygen consumption decreased as a functio n of time when exposed to sporulation medium. Apparently, the decrease of metabolic rates was not due to alkalinization. By systematically v arying the cell concentration in sporulation medium from 1.4 x 10(7) t o 20 x 10(7) cell ml(-1), the percentage of sporulating cells was foun d to decrease in parallel with the rate of acetate consumption. When t he sporulation efficiency attained under the different experimental co nditions was plotted as a function of the rate of acetate consumption, a linear correlation was found. Anabolic fluxes estimation revealed a decrease of the rate through gluconeogenic and glyoxylate pathways oc curring during sporulation progression. The pattern of metabolic fluxe s progressively evolved toward a predominance of more oxidative catabo lic fluxes than those exhibited under growth conditions. The results o btained are discussed in terms of a characteristic pattern of metaboli c fluxes and energetics, associated to the development of yeast sporul ation.