text: B. subtilis is a soil-dwelling microbe that uses quorum sensing to regulate two different biological processes: competence and sporulation.  During stationary growth phase when B. subtilis are at high cell density, approximately 10% of the cells in a population are induced to become competent.  It is believed that this subpopulation becomes competent to take up DNA that could potentially be used for the repair of damaged (mutated) chromosomes.   ComX (also known as competence factor) is a 10-amino acid peptide that is processed from a 55-amino acid peptide precursor.  Like most autoinducers, ComX is secreted and accumulates as a function of cell density.  Once a threshold extracellular level is achieved, ComX is detected by a two-component ComP/ComA sensor kinase/response regulator pair.  Phosphorylation of ComA activates the expression of comS gene, ComS inhibits the degradation of ComK, and finally ComK activates the expression of a number of genes required for competence.
  Sporulation, on the other hand, is a physiological response of B. subtilis to depletion of nutrients within a particular environment.   It is also regulated by extracellular signaling.  When B. subtilis populations sense waning conditions, they respond by undergoing asymmetric cell division.  This ultimately produces spores that are adapted for dispersal and survival in unfavorable conditions.   Sporulation in B. subtilis is mediated by CSF (sporulation factor), a pentapeptide cleaved from the precursor peptide PhrC.   CSF is secreted into the extracellular environment and is taken back up into cells via the ABC transporter Opp where it acts intracellularly.   While low internal concentrations of CSF contribute to competence, high concentrations induce sporulation.  CSF inhibits a phosphatase, RabB, which increases the activity of Spo0A, favoring a switch in commitment from competence to the sporulation pathway