title: New insights into the pneumococcal fratricide: relationship to clumping and identification of a novel immunity factor.
abstract: In 1971, Tomasz and Zanati discovered that competent pneumococci have a tendency to form aggregates when pelleted by centrifugation and resuspended in 0.01 N HCl by brief vortexing. Interestingly, no clumping was observed with parallel cultures of non-competent cells treated in the same way. We set out to elucidate the mechanism behind this striking phenomenon, and were able to show that it depends on extracellular DNA that is presumably released by so-called competence-induced cell lysis. Competence-induced cell lysis, which was first described a few years ago, seems to rely on the concerted action of several murein hydrolases. Our results confirmed and extended previous findings by showing that competence-induced aggregation is abolished in a lytA-lytC double mutant, and absolutely requires CbpD and its N-terminal CHAP amidase domain. Furthermore, we discovered a novel competence stimulating peptide (CSP)-induced immunity protein, encoded by the early competence gene comM (spr1762), which protects competent pneumococci against their own lysins. Together, the murein hydrolases and the immunity protein constitutes a CSP-controlled mechanism that allows competent pneumococci to commit fratricide by killing non-competent pneumococci sharing the same ecological niche. Through such predatory behaviour, pneumococci can get access to transforming DNA and nutrients, promote the release of virulence factors, and at the same time get rid of competitors.
authors.affiliation: Laboratoire de Microbiologie et Génétique Moléculaires, UMR 5100 CNRS-Université Paul Sabatier, 118 route de Narbonne, 31062 Toulouse Cedex, France. sigve.havarstein@umb.no
authors.forename: Leiv Sigve
authors.initials: LS
authors.lastname: Håvarstein
authors.forename: Bernard
authors.initials: B
authors.lastname: Martin
authors.forename: Ola
authors.initials: O
authors.lastname: Johnsborg
authors.forename: Chantal
authors.initials: C
authors.lastname: Granadel
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Claverys
mesh_terms: D018829:Adhesins, Bacterial / Q000235:genetics; D001426:Bacterial Proteins / Q000235:genetics*; D004247:DNA / Q000378:metabolism; D005798:Genes, Bacterial; D009154:Mutation; D009238:N-Acetylmuramoyl-L-alanine Amidase / Q000235:genetics*; D010455:Peptides / Q000235:genetics / Q000276:immunology; D013296:Streptococcus pneumoniae / Q000235:genetics / Q000378:metabolism / Q000472:pathogenicity*; D014169:Transformation, Bacterial / Q000235:genetics*
chemical_list: D018829:Adhesins, Bacterial; D001426:Bacterial Proteins; D010455:Peptides; D004247:DNA; C419222:LytC protein, Streptococcus; D009238:N-Acetylmuramoyl-L-alanine Amidase