Effects of potassium on the ethanol production rate of Saccharomyces cerevisiae carrying the plasmid pCYG4 related with ammonia assimilation.

The influence of potassium on ethanol production by Saccharomyces cerevisiae wild type and AR5 cells carrying the plasmid pCYG4 was investigated. This plasmid carries the glutamate dehydrogenase gene conferring an 11-fold higher level of expressed enzyme activity over the wild type cells. All experiments were carried out in batch culture with medium supplemented to different potassium concentrations up to 180 mM. Maximum ethanol production rate was observed in the AR5 cells grown in medium supplemented with 3.5 mM of potassium ions. Glucose uptake rate increased with increasing potassium up to 60 mM, but higher concentrations depressed glucose uptake rate in both strains. Furthermore, the wild type cells showed higher growth rate, ethanol production, and glucose consumption rate than the AR5 cells. These lower rates in the AR5 cells could be explained by repression of potassium uptake by an enhancement of ammonium feeding, and greater energy requirements by these cells due the presence of the plasmid.