Effect of sodium chloride on growth characteristics of the marine yeast Debaryomyces hansenii in batch and continuous culture under carbon and potassium limitation

Abstract

Debaryomyces hansenii has been grown in relatively large volume (> 1 l) batch culture in media with initial pH of 5·0, 7·2 and 8·3 in the presence and absence of added 1·5 m -NaCl. The pH of the medium was either maintained or allowed to change. The characteristics of growth appeared to be very similar in all treatments, except that the lag phase was extended by the presence of 1·5 MNaCl. The yeast was also grown in continuous culture under carbon limitation in the presence or absence of added 1·5 M-NaCl with the pH either uncontrolled or maintained at pH 8·3. Step-up studies showed that the yeast adjusts osmotically by two mechanisms. One is relatively short-term and involves an influx of sodium while the other involves the loss of sodium from the cell. Both are associated with the synthesis of glycerol. Analysis of yields of biomass and mol content of solutes within the cells, both per mol of glucose utilized, showed that at the lower specific growth rates cells were glucose-limited but energy-limited at higher rates. The specific growth rate at which the cells became energy-limited was lower in saline media (and lowest when the pH was maintained at 8·3). When the culture was glucose limited, in non-saline conditions, growth was very much dependent on the absorption of potassium, whose intracellular content per mol of glucose utilized was much greater than that of any other measured solute. In saline conditions with an acidic medium, much of the glucose utilized was expended in generating the appropriate solute potential primarily with glycerol and sodium. The conditions under which the cells are energy-limited are considered in relation to the futile cycling of glycerol and the maintenance of an appropriate gradient of protons across the plasmalemma in an alkaline medium. Potassium-limitation in continuous culture was studied in media of low salinity and of high salinity (0·5 m -NaCl) with the pH either uncontrolled externally or maintained at either 5·5 or 8·3. The major osmolytes appeared to be potassium and glycerol in low salinity media and sodium, glycerol and arabitol in 0·5 m -NaCl. The relationship between yield and the internal concentration of potassium per mol of glucose utilized for any one medium indicated that the production of biomass and the uptake of potassium are closely related. Glycerol concentration per mol of glucose utilized was proportional to yield in all media; at pH 8·3 in the 0·5 m -NaCl medium relatively less arabitol was produced. The highest cellular concentrations of sodium and glycerol were observed in this medium at the higher specific growth rates. These studies confirm previous data showing that in saline media growth of the yeast under alkaline conditions is physiologically different from that in acid conditions.