title: Secretion of a pneumococcal type II secretion system pilus correlates with DNA uptake during transformation.
abstract: Streptococcus pneumoniae is a major human pathogen that successfully adapts to the host environment via an efficient uptake system for free DNA liberated from other organisms in the upper respiratory tract, facilitating immune evasion and drug resistance. Although the initial signaling events leading to pneumococcal competence for DNA transformation and the fate of DNA when it has been taken up have been extensively studied, the actual mechanism by which DNA in the environment may traverse the thick capsular and cell wall layers remains unknown. Here we visualize that induction of competence results in the formation of a native morphologically distinct pilus structure on the bacterial surface. This plaited pilus is encoded by the competence (com)G locus, and, after assembly, it is rapidly released into the surrounding medium. Heterologous pneumococcal pilus expression in Escherichia coli was obtained by replacing the pulE-K putative pilin genes of the Klebsiella oxytoca type II secretion system with the complete comG locus. In the pneumococcus, the coordinated secretion of pili from the cells correlates to DNA transformation. A model for DNA transformation is proposed whereby pilus assembly "drills" a channel across the thick cell wall that becomes transiently open by secretion of the pilus, providing the entry port for exogenous DNA to gain access to DNA receptors associated with the cytoplasmic membrane.
authors.affiliation: Department of Microbiology, Tumor and Cell Biology, Karolinska Institutet, SE-171 77 Stockholm, Sweden.
authors.forename: Murat
authors.initials: M
authors.lastname: Balaban
authors.forename: Patrick
authors.initials: P
authors.lastname: Bättig
authors.forename: Sandra
authors.initials: S
authors.lastname: Muschiol
authors.forename: Stephan M
authors.initials: SM
authors.lastname: Tirier
authors.forename: Florian
authors.initials: F
authors.lastname: Wartha
authors.forename: Staffan
authors.initials: S
authors.lastname: Normark
authors.forename: Birgitta
authors.initials: B
authors.lastname: Henriques-Normark
mesh_terms: D058947:Bacterial Secretion Systems / Q000502:physiology*; D004247:DNA / Q000378:metabolism*; D061269:DNA Transformation Competence / Q000235:genetics*; D004591:Electrophoresis, Polyacrylamide Gel; D010861:Fimbriae, Bacterial / Q000378:metabolism* / Q000648:ultrastructure; D046529:Microscopy, Electron, Transmission; D013296:Streptococcus pneumoniae / Q000378:metabolism*; D014169:Transformation, Bacterial / Q000235:genetics / Q000502:physiology*; D014238:Trichloroacetic Acid
chemical_list: D058947:Bacterial Secretion Systems; D014238:Trichloroacetic Acid; D004247:DNA