Impact of an osmotic stress on the intracellular volume of Hansenula anomala

Abstract

The effect of an osmotic stress resulting from high glucose or NaCl concentrations on the morphology and intracellular volume of Hansenula anomala was examined by scanning electronic microscopy and changes in the intracellular volume accessible to tritiated water, respectively. No noticeable change in the cell morphology was observed, with the cells remaining ellipsoidal. An increase in the contribution of compatible solutes, such as arabitol, glycerol and trehalose, to the cell volume, was not sufficient to counterbalance the decrease in the volume accessible to tritiated water for increasing water stress, leading to a decrease in cell volume. For a given morphology, a decrease in the cell volume allowed the cell to maximize the surface to ratio volume for a better distribution of the external osmotic pressure. It also allowed maximization of the compatible solute concentration (for a given amount of accumulated compounds), leading to an increase in the internal osmotic potential to counterbalance the osmotic potential of the surrounding medium. However, the accumulation of compatible solutes in the cell did not allow any adjustment of the osmotic potential of cells in high-osmolarity medium, especially in the case of NaCl as the osmoticum, thereby confirming the higher stress effect of salt relative to glucose.