Choline-Binding Protein D (CbpD) inStreptococcus pneumoniaeIs Essential for Competence-Induced Cell Lysis

Abstract

Streptococcus pneumoniae is an important human pathogen that is able to take up naked DNA from the environment by a quorum-sensing-regulated process called natural genetic transformation. This property enables members of this bacterial species to efficiently acquire new properties that may increase their ability to survive and multiply in the human host. We have previously reported that induction of the competent state in a liquid culture of Streptococcus pneumoniae triggers lysis of a subfraction of the bacterial population resulting in release of DNA. We have also proposed that such competence-induced DNA release is an integral part of natural genetic transformation that has evolved to increase the efficiency of gene transfer between pneumococci. In the present work, we have further elucidated the mechanism behind competence-induced cell lysis by identifying a putative murein hydrolase, choline-binding protein D (CbpD), as a key component of this process. By using real-time PCR to estimate the amount of extracellular DNA in competent relative to noncompetent cultures, we were able to show that competence-induced cell lysis and DNA release are strongly attenuated in a cbpD mutant. Ectopic expression of CbpD in the presence or absence of other competence proteins revealed that CbpD is essentially unable to cause cell lysis on its own but depends on at least one additional protein expressed during competence.

Fratricide in Streptococcus pneumoniae: contributions and role of the cell wall hydrolases CbpD, LytA and LytC

“…Our results show that only about 0.4 % of the target cells are lysed when the lytA and lytC genes have been deleted in both attacker and target cells, demonstrating that CbpD is not very effective on its own under the conditions used (Table 2). Nevertheless, CbpD is an essential component of the lysis mechanism, as attacker cells lacking this protein are totally unable to kill and lyse their non-competent siblings (Kausmally et al, 2005; Table 2). When CbpD is present, LytA and LytC both play an important role in the lysis process.…”

“…In addition, a few CSP-responsive genes are involved in the predatory lysis mechanism described above (for a review, see Claverys & Håvarstein, 2007). These include the early competence gene comM (Håvarstein et al, 2006), and the two late competence genes cbpD and lytA (Steinmoen et al, 2003;Guiral et al, 2005;Kausmally et al, 2005). The comM gene encodes an immunity protein that protects the competent cells against their own lysins ( Håvarstein et al, 2006).…”

Discovery of Immunodominant B Cell Epitopes within Surface Pneumococcal Virulence Proteins in Pediatric Patients with Invasive Pneumococcal Disease

“…Importantly, all identified epitopes are located within functional surface proteins, implying that antibodies against these epitopes could inhibit major functions of the bacterium associated with impaired invasive capacity and virulence. One epitope was identified within CbpD that is involved in adherence, complement inhibition, and competence-induced cell lysis (13). Two epitopes have been identified within PhtE and three epitopes within PhtD.…”

Versatility of pneumococcal surface proteins

“…Recent reports indicate that CbpD is a competence-stimulating-peptide-inducible protein, and a function as a murein hydrolase has been proposed. CbpD has been demonstrated to assist LytA in competenceinduced cell lysis (Kausmally et al, 2005). A further study has provided experimental evidence that the biological activity of CbpD is involved in the ability of competent bacteria to trigger the release of virulence factors from noncompetent S. pneumoniae (Guiral et al, 2005).…”