Differentiation of vegetative cells into spores: a kinetic model applied toBacillus subtilis

Abstract

AbstractBacterial spores are formed within vegetative cells as thick-walled bodies resistant to physical and chemical treatments which allow the persistence and dissemination of the bacterial species. Spore-forming bacteria are natural contaminants of food raw materials and sporulation can occur in many environments from farm to fork. In order to predict spore formation over time, we developed a model that describes both the kinetics of growth and the differentiation of vegetative cells into spores. The model includes a classical growth model with the addition of only two sporulation-specific parameters: the probability of each vegetative cell to sporulate, and the time needed to form a spore once the cell is committed to sporulation. The growth-sporulation model was evaluated using the spore-forming, Gram positive bacterium,Bacillus subtilisand the biological meaning of the sporulation-specific parameters was validated using a derivative strain that produces the green fluorescent protein as a marker of sporulation initiation. The model accurately describes the growth and the sporulation kinetics in different environmental conditions and further provides valuable, physiological information on the temporal abilities of vegetative cells to differentiate into spores.ImportanceThe growth-sporulation model we developed accurately describes growth and sporulation kinetics. It describes the progressive transition from vegetative cells to spores with sporulation parameters which are meaningful and relevant to the sporulation process. The first parameter is the mean time required for a vegetative cell to differentiate into a spore (i.e. the duration of the sporulation process). The second sporulation parameter is the probability of each vegetative cell forming a spore over time. This parameter assesses how efficient the sporulation process is, how fast vegetative cells sporulate and how synchronous the bacterial population is for sporulation. The model constitutes a very interesting tool to describe the growth and the sporulation kinetics in different environmental conditions and it provides qualitative information on the sporulation of a bacterial population over time.