Natural genetic competence is the ability of cells to take up exogenous DNA. It depends on achieving a specialized cellular state and as it provides a mechanism for allele exchange it is not surprising that it might occur in response to the presence of a large numbers of cells of the same species which are obviously potential gene donors

Competence regulation in Bacillus subtilis

In B. subtilis competent cells produce a small number of proteins that can bind and take up DNA. Production of this DNA-uptake machinery depends on the competence transcription factor ComK which is subject to autophosphorylation. The transcription-enhancing activity of comK is generally inhibited during exponential growth by direct interaction of ComK with MecA and MecB. This inhibition can be relieved by a small protein ComS which is synthesized in response to a modified peptide pheromone that accumulates in the culture medium of B.subtilis strains when they are grown to high cell density. The precursor of this peptide pheromone is encoded by comX. A sensor (ComP) and a response regulator (ComA) mediate the cellular response to the peptide pheromone

Competence regulation in Streptococcus pneumoniae

In contrast to the competence phenotype of B. subtilis, that of S. pneumoniae arises at early- or mid-logarithmic growth phase and persists for only a limited period of time. The importance of this mechanism of genetic exchange is demonstrated by the evolution of new penicillin-resistant penicillin binding proteins by the acquisition of gene segments from other oral streptococci.

The competence-inducing signal, or pheromone, is a 17-residue peptide termed the competence stimulating peptide (CSP). The 41-residue precursor of CSP, encoded by comC, has a characteristic N-terminal pro-sequence containing a Gly-Gly cleavage motif, which is commonly found in the precursor sequences of class II antimicrobial peptides. There are now known to be two allelic variants of this peptide pheromone, designated comC1 and comC2, which differ from one another at eight residues. The genes encoding the two-component regulatory system (comD and comE), encoding a sensor and a response regulator, respectively, are directly downstream of the comC gene. Transcription of the comCDE genes depends directly on ComE, indicating that the locus is autoregulatory. The secretion and have bennthe ABC exporters involved in the secretion of class II AMPs.