The osmotic stress tolerance of basidiomycetous yeasts

Abstract

The growth and accumulation of intracellular polyols at reduced water activity (a_w) were studied in 40 basidiomycetous yeast strains. The growth of most strains showed greater tolerance to NaCl than sorbitol at the same a_w. No strain was able to grow below 0.90a_w. ¹³C nuclear magnetic resonance spectroscopy revealed that glycerol was the major solute accumulated intracellularly by all the yeasts when grown to 0.96a_w (NaCl). Arabitol or mannitol was also accumulated in some yeasts, whereas a few only accumulated glycerol. Analysis of six yeasts in detail revealed that the intracellular glycerol concentrations of five yeasts increased significantly when grown at 0.96a_w (NaCl or sorbitol) compared with growth at 0.998a_w. Arabitol and mannitol concentrations also increased, but not to the same degree. Intracellular potassium concentrations decreased when grown at 0.96a_w (NaCl or sorbitol) and sodium increased, but only when grown at 0.96a_w (NaCl). The survival of nine strains was evaluated in soil cultures and it was found that all grew at 100% field capacity, whereas at lower field capacity, only some strains grew or survived. The growth of basidiomycetous yeasts appears to be more sensitive to reduced a_w than ascomycetous yeasts.