Stochastic strategies for survival: Bacterial competence in Bacillus Subtilis

Under stressful environments, organisms take actions that help them protect their DNA. An example of such actions is the stochastic switching that Bacillus subtilis undergoes, in which it goes from the vegetative state to a competent state. When in competence, the cell has an increased ability to bind to and internalize exogenous DNA. This increases the chances of survival of a cell. Competence is nonetheless an expensive state for the cell to be in, so the decision to switch undergoes a very delicate regulation. A major player in controlling the switching of the cell is the ComK protein. ComK protein is a key regulator which activates hundreds of genes, including the genes encoding the DNA-uptake and recombination systems. In Bacillus subtilis, stress in the environment activates a sequence of chemical reactions that, driven by cellular noise, stochastically increases the level of ComK in some bacterial cells driving them from their original vegetative state into a competent state. In this work, we use the Finite State Projection (FSP) method to analyze stochastic biochemical events and to study the excitable dynamics responsible for competence in Bacillus Subtilis. We compute the probability with which Bacillus subtilis enters in competence. We also present a method to analyze the sensitivity of these stochastic events to various system parameters such as binding affinities, transcription rates, degradation rates, etc.