| Quorum sensing is the ability of bacteria to control gene expression by monitoring their population density. In Bacillus subtilis, two extracellular signaling peptides, ComX pheromone and Competence and Sporulation Factor (CSF), stimulate the activity of the transcription factor ComA, which activates several genes involved in the quorum response. Interestingly, genetic polymorphisms between strains of B. subtilis have been shown to exist in the genes involved in the production of and response to ComX pheromone, the comQXP locus. These genetic polymorphisms lead to strain-specific interaction between ComX pheromone and ComP. We investigated whether the CSF signaling peptide exhibits similar strain specificity. We sequenced PCR amplified products from the rapC phrC locus of three strains each of B. subtilis and B. mojavensis and determined that hypervariable regions within this region do not exist. We present evidence that these strains produce extracellular CSF and that CSF can partially compensate for the lack of communication between strains producing different ComX pheromone. Our results suggest that, while Comx represents a strain-specific signaling molecule, CSF is a conserved species-specific signaling molecule.; CSF belongs to the Phr family of signaling peptides in B. subtilis that function by regulating a Rap protein. In looking for Rap homologs in other bacteria, one protein, NprR of Bacillus thuringiensis, was of particular interest because it appears to have homology to the Rap proteins at its C-terminus, but unlike the Rap proteins, to also have a DNA binding domain at its N-terminus. In addition, there is a small open reading frame downstream of nprR that has characteristics of a Phr signaling peptide precursor protein which we have denoted as nprX. Immediately downstream of the nprR nprX locus is nprB, whose product has homology to neutral proteases. We present evidence in support of our hypothesis that the NprR transcription factor regulates expression of the neutral protease, NprB, and that an extracellular signaling peptide derived from nprX is required for this regulation. |
