Effects of temperature, pH and water activity on the growth and the sporulation abilities of Bacillus subtilis BSB1.

Spore-forming bacteria are implicated in cases of food spoilage or food poisoning. In their sporulated form, they are resistant to physical and chemical treatments applied in the food industry and can persist throughout the food chain. The sporulation leads to an increase in the concentration of resistant forms in final products or food processing equipment. In order to identify sporulation environments in the food industry, it is necessary to be able to predict bacterial sporulation according to environmental factors. As sporulation occurs after bacterial growth, a kinetic model of growth-sporulation was used to describe the evolution of vegetative cells and spores through time. The effects of temperature, pH and water activity on the growth and the sporulation abilities of Bacillus subtilis BSB1 were modelled. The values of the growth boundaries were used as inputs to predict these effects. The good description of the sporulation kinetics by growth parameters suggests that the impact of the studied environmental factors is the same on both physiological process. Suboptimal conditions for growth delay the appearance of the first spores, and spores appear more synchronously in suboptimal conditions for growth. The developed model was also applicable to describe the growth and sporulation curves in changing temperature and pH conditions over time.