The Effect of Water Activity and aw‐Controlling Solute on Sporulation of Bacillus cereus

The influence of water activity (aw) on the formation of phase bright, heat stable, and dipicoiir.ic acid‐containing spores of Bacillus cereus T from stage III to stage IV forespores has beer. investigated. Decreasing a w levels reduced the rate of sporulation and the number of forespores which lysed was determined by the a w ‐controlling solute used. The limiting a w value for ir.e formation of mature spores was about 0·95 for glucose, sorbitol and NaCl whereas it was about 0·91 for glycerol. The development of refractility. the synthesis of dipicolinic acid, and acquisition of heat stability were affected equally by decrease in a w during sporulation. With the range of a w value where spores could be formed NaCl and glycerol had no signifcant: influence on the D value of the resulting spores whereas at all a w levels, when sorbitol was use: as the a w ‐controlling solute, the heat resistance was greater than in the basal medium. It Is suggested that the a w of the sporulation medium determines the quantity of spores rather than. the spore properties.