Fratricide is essential for efficient gene transfer between pneumococci in biofilms.
Streptococcus pneumoniae and a number of commensal streptococcal species are competent for natural genetic transformation. The natural habitat of these bacteria is multispecies biofilms in the human oral cavity and nasopharynx. Studies investigating lateral transfer of virulence and antibiotic resistance determinants among streptococci have shown that interspecies as well as intraspecies gene exchange takes place in these environments. We have previously shown that the action of a competence-specific murein hydrolase termed CbpD strongly increases the rate of gene transfer between pneumococci grown in liquid cultures. CbpD is the key component of a bacteriolytic mechanism termed the fratricide mechanism. It is secreted by competent pneumococci and mediates the release of donor DNA from sensitive streptococci present in the same environment. However, in nature, gene exchange between streptococci takes place in biofilms and not in liquid cultures. In the present study, we therefore investigated whether CbpD affects the rate of gene transfer in laboratory-grown biofilms. Our results show that the fratricide mechanism has a strong positive impact on intrabiofilm gene exchange, indicating that it is important for active acquisition of homologous donor DNA under natural conditions. Furthermore, we found that competent biofilm cells of S. pneumoniae acquire a Nov(r) marker much more efficiently from neighboring cells than from the growth medium. Efficient lysis of target cells requires that CbpD act in conjunction with the murein hydrolase LytC. In contrast, the major autolysin LytA does not seem to be important for fratricide-mediated gene exchange in a biofilm environment.
Department of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, Ås, Norway.
Hua
H
Wei
Leiv Sigve
LS
Håvarstein
D000581:Amidohydrolases / Q000378:metabolism*; D001426:Bacterial Proteins / Q000378:metabolism*; D001433:Bacteriolysis; D018441:Biofilms / Q000254:growth & development*; D061269:DNA Transformation Competence; D022761:Gene Transfer, Horizontal; D009238:N-Acetylmuramoyl-L-alanine Amidase / Q000378:metabolism; D013296:Streptococcus pneumoniae / Q000235:genetics / Q000502:physiology*
D001426:Bacterial Proteins; D000581:Amidohydrolases; C569012:CbpD protein, Streptococcus pneumoniae; C419222:LytC protein, Streptococcus; D009238:N-Acetylmuramoyl-L-alanine Amidase