title: Association of a novel high molecular weight, serine-rich protein (SrpA) with fibril-mediated adhesion of the oral biofilm bacterium Streptococcus cristatus.
abstract: The surface of the oral plaque bacterium Streptococcus cristatus is decorated with a lateral tuft of fibrils. The fibrillar tuft functions in the adhesion of S. cristatus to heterologous bacterial species in the plaque biofilm. The tuft typically consists of a densely packed fringe of shorter fibrils 238 +/- 19 nm long with longer, less abundant fibrils 403 +/- 66 nm long projecting through the fringe of short fibrils. The two types of fibrils in the tufts of S. cristatus have been refractory to biochemical separation, complicating their characterization. A hexadecane partition assay was used to enrich for subpopulations of S. cristatus CR311 (type strain NCTC 12479) having distinct fibrillar morphotypes. Negative staining in the TEM revealed that cells of a hydrophobic subpopulation of S. cristatus (CR311var1) carried only the long fibrils (395 +/- 32 nm). A hydrophilic subpopulation of S. cristatus (CR311var3) consisted of mixed morphotypes having no fibrils or remnant short fibrils (223 +/- 49 nm). No long fibrils were observed on any cells in the CR311var3 subpopulation. The CR311var3 morphotype, unlike the wild-type strain and CR311var1, was not able to form corncobs with either Corynebacterium matruchotii or Fusobacterium nucleatum. Variant CR311var3 did not express the novel gene srpA, which encodes a high molecular weight (321,882 Da) serine-rich protein, SrpA. The SrpA protein contains two extensive repeat motifs of 17 and 71 amino acids and a gram-positive cell wall anchor consensus sequence (LPNTG). The unusual properties of SrpA most closely resemble those of Fap1, the fimbrial-associated adhesin protein of Streptococcus parasanguis. The association of long fibrils, high surface hydrophobicity, ability to form corncob formations, and expression of the srpA gene suggest that SrpA is a long fibril protein in S. cristatus.
authors.affiliation: Department of Biological Sciences, Manchester University, Manchester, M13 9PT, UK.
authors.forename: P S
authors.initials: PS
authors.lastname: Handley
authors.forename: F F
authors.initials: FF
authors.lastname: Correia
authors.forename: K
authors.initials: K
authors.lastname: Russell
authors.forename: B
authors.initials: B
authors.lastname: Rosan
authors.forename: J M
authors.initials: JM
authors.lastname: DiRienzo
mesh_terms: D000595:Amino Acid Sequence; D001422:Bacterial Adhesion / Q000235:genetics / Q000502:physiology; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D018441:Biofilms; D002874:Chromosome Mapping; D003773:Dental Plaque / Q000382:microbiology / Q000648:ultrastructure; D010861:Fimbriae, Bacterial / Q000235:genetics* / Q000648:ultrastructure; D006801:Humans; D008969:Molecular Sequence Data; D012694:Serine / Q000737:chemistry; D013045:Species Specificity; D013291:Streptococcus / Q000235:genetics* / Q000502:physiology / Q000648:ultrastructure
chemical_list: D001426:Bacterial Proteins; D012694:Serine