A Relation Between Cell Multiplication and Alcohol Tolerance in Yeasts

Abstract

Studies on the multiplication of four strains of Saccharomyces cerevisiae Hansen and two strains of Hansenula anomala (Hansen) Sydow under various conditions revealed reductions in growth which parallel the lowered glucose utilization rates previously reported. Population curves for cultures containing various amounts of ethanol resemble those for glucose utilization by the same yeasts under similar conditions. A decrease in alcohol tolerance with elevated temperature is accompanied by reduced multiplication. Cells of the same yeast from aerated and nonaerated inocula, which exhibit differences in alcohol, also attain different population levels in the presence of ethanol. The primary effects of ethanol on yeast growth are reduction in the total number of cells formed and lowering of the exponential multiplication rate. Results of experiments involving estimation of cell numbers and glucose utilization in the same cultures indicate that the first effect of added ethanol is probably a reduction in multiplication, with glucose utilization by the culture as a whole declining only later. It is suggested that the decreased growth effected by ethanol results not only in fewer active cells, but also in the accumulation of high-energy phosphate bonds. These two effects, which result in a reduction in glucose utilization, could account for the occurrence of the phenomenon of alcohol tolerance.