Solute stresses affect growth patterns, endogenous water potentials and accumulation of sugars and sugar alcohols in cells of the biocontrol yeast Candida sake

Aim: To evaluate the effect of modifications of water activity (a(W) 0.996-0.92) of a molasses medium with different solutes (glycerol, glucose, NaCl, proline or sorbitol) on growth, intracellular water potentials (psi (c)) and endogenous accumulation of polyols/sugars in the biocontrol yeast Candida sake. Methods and Results: Modification of solute stress significantly influenced growth, psi (c) and accumulation of sugars (glucose/trehalose) and polyols (glycerol, erythritol, arabitol and mannitol) in the yeast cells. Regardless of the solute used to modify a(W), growth was always decreased as water stress increased. Candida sate cells grew better in glycerol- and proline-amended media, but were sensitive to NaCl. The psi (c) measured using psychrometry showed a significant effect of solutes, a, and time. Cells from the 0.96 a(W) NaCl treatment presented the lowest psi (c) value (-5.20 MPa) while cells from unmodified media (a(w) = 0.996) had the highest value (-0.30 MPa). In unmodified medium, glycerol was the predominant reserve accumulated. Glycerol and arabitol were the major compounds accumulated in media modified with glucose or NaCl. In proline media, the concentration of arabitol increased. In glycerol- and sorbitol-amended media, the concentration of glycerol rose. Some correlations were obtained between compatible solutes and psi (c). Conclusions and Significance: This study demonstrates that subtle changes in physiological parameters significantly affect the endogenous contents of C. sake cells. It may be possible to utilize such physiological information to develop biocontrol inocula with improved quality.