Microbial growth at reduced water activities: some physicochemical properties of compatible solutes.

The water activities (aw) of solutions of D-arabitol (a major compatible solute in yeasts grown at reduced aw) and also of related polyols (L-arabitol, xylitol and ribitol) were determined at 25 degrees C. The aw of saturated solutions of L-proline and monopotassium L-glutamate (solutes which accumulate in bacterial cells at reduced aw) were also determined. The viscosities of L-proline, monopotassium L-glutamate and D-arabitol solutions were measured at 25, 30, 35 and 40 degrees C for various concentrations up to high molalities. The relative viscosity curves were described using a theoretical model for the concentration dependence of viscosity. No relationship of viscosity of the electrolytes to effectiveness as 'compatible solutes' were evident, neither were the compatible solutes particularly effective 'structure makers' or 'structure breakers.'