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.