The role of physiological state in osmotolerance of the salt-tolerant yeast Debaryomyces hansenii

Great variations in tolerance to osmotic dehydration during batch growth of the salt-tolerant yeast Debaryomyces hansenii have been demonstrated. The variations in osmotolerance were dependent on the cultivation conditions. The cells developed osmosensitivity at the beginning of the growth period. In medium in which the nitrogen source of the cells was changed from ammonium to urea during the growth cycle, the resulting transition state induced a marked increase in the osmotolerance of the cells. However, when the pH was kept constant at 6.0, the osmosensitive period disappeared almost completely. Various possible osmotolerance factors, such as the intracellular polyol and ion concentrations, the "G3P shuttle," and the cells' total activity measured by means of microcalorimetry, have been studied. Only small variations in the intracellular pools of polyols and ions were observed during different cultivation conditions and phases of growth. No single factor seems to be the determinant for osmotolerance and the overlap between osmoregulatory and osmotolerance factors is limited.