The influence of different carbon sources and medium osmolarity on the potassium requirements of Candida utilis NCYC 321, growing in continuous culture

Abstract

In order to study the influence of different carbon sources on the K⁺-requirements of Candida utilis NCYC 321, this yeast was grown at several different dilution rates in potassium-limited continuous cultures with either glucose, glycerol, ethanol, citrate or lactate serving as the carbon and energy source.

It was found that the nature of the carbon source profoundly influenced the cellular potassium content, especially at low dilution rates, but that these differences could not be correlated with any differences in relative growth rate (i.e., α/α _max. And although small amounts of potassium seemingly were needed to serve in osmoregulation and in the cotransport of some acidic carbon sources (lactate and citrate), these requirements were negligible.

Independent of carbon source, a strong correlation existed between the intracellular potassium concentration and the yield value on oxygen (Y _O), and between cellular potassium concentration and growth rate. From these two correlations it was concluded that potassium probably was involved mainly in processes associated with ATP synthesis in this yeast.

Finally the effect of the addition of NaCl to the medium was tested with glucose-containing cultures that were either carbon- or potassium-limited. Up to a concentration of 20 g/l, NaCl was without influence on Y _O, Y _glucose and q _{O 2}, but effected a slight increase in the cellular potassium content of the potassium-limited cells and a decrease in that of the glucose-limited cells.