Genetic Diversity of the Streptococcal Competence ( com ) Gene Locus

Abstract

The com operon of naturally transformable streptococcal species contains three genes, comC, comD, andcomE, involved in the regulation of competence. ThecomC gene encodes a competence-stimulating peptide (CSP) thought to induce competence in the bacterial population at a critical extracellular concentration. The comD and comEgenes are believed to encode the transmembrane histidine kinase and response regulator proteins, respectively, of a two-component regulator, with the comD-encoded protein being a receptor for CSP. Here we report on the genetic variability of comCand comD within Streptococcus pneumoniaeisolates. Comparative analysis of sequence variations ofcomC and comD shows that, despite evidence for horizontal gene transfer at this locus and the lack of transformability of many S. pneumoniae strains in the laboratory, there is a clear correlation between the presence of a particular comCallele and the cognate comD allele. These findings effectively rule out the possibility that the presence of noncognatecomC and comD alleles may be responsible for the inability to induce competence in many isolates and indicate the importance of a functional com pathway in these isolates. In addition, we describe a number of novel CSPs from disease-associated strains of S. mitis and S. oralis. The CSPs from these isolates are much more closely related to those fromS. pneumoniae than to most CSPs previously reported fromS. mitis and S. oralis, suggesting that these particular organisms may be a potential source of DNA in recombination events generating the mosaic structures commonly reported in genes ofS. pneumoniae that are under strong selective pressure.

Genetic variation incomC, the gene encoding competence-stimulating peptide (CSP) inStreptococcus mutans

“…Therefore, the loss of the three amino acids (-LGK) at the carboxyl end of the peptide (CSP-2 & CSP-3) or substitution of tyrosine for serine at position 3 of the mature CSP (CSP-3) does not impair the function of these peptides. Furthermore, in contrast to the pherotype specificity reported in S. pneumoniae (Pozzi et al, 1996;Whatmore et al, 1999), representative strains encoding either CSP-1 or CSP-2 showed increased transformation in response to all three mature synthetic CSPs. Therefore, distinct strains of S. mutans can readily cooperate in genetic exchange.…”

Allelic variation in a peptide-inducible two-component system of Streptococcus pneumoniae

“…Sequence comparison of the deduced peptide in a total of 10 strains revealed another 28-residue variant (Table 1). Thus, the signaling molecule and the sensor domain of the receptor kinase occur as distinct functional units, similar to the allelic variants described for the comC/comD pair where activation of the receptor kinase requires the presence of the matching peptide ( [17,18] and references therein).…”

Regulation of natural genetic transformation and acquisition of transforming DNA inStreptococcus pneumoniae

“…Following the initial identification of the comC gene in strain CP1200 (Håvarstein et al, 1995a), this gene has been sequenced in a large number of strains from species such as S. pneumoniae, Streptococcus mitis, Streptococcus oralis and other members of the mitis phylogenetic group (Pozzi et al, 1996;Håvarstein et al, 1997;Ramirez et al, 1997;Whatmore et al, 1999;Johnsborg et al, 2007a). This work has revealed that there exists extensive diversity with respect to the primary amino acid sequences of CSPs produced by various strains and species.…”