Competence for transformation: a matter of taste.

Genetic competence in both Bacillus subtilis and Streptococcus pneumoniae, as well as virulence in Staphylococcus aureus, are regulated by quorum-sensing mechanisms that use two-component signal transduction systems to respond to extracellular peptide pheromones. Recent data indicate that in all three systems closely related strains express markedly different pheromones and polytopic membrane receptor proteins. This polymorphism may function as a sexual isolation mechanism. In B. subtilis the downstream segment of the competence regulatory pathway acts by controlling the stability of a key transcription factor. In S. pneumoniae the downstream segment involves the transcriptional activation of a minor sigma factor that is in turn responsible for the expression of late competence genes.