The osmotic stress tolerance of basidiomycetous yeasts

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.