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. Keywordscorncobs; fibrils; SrpA; Streptococcus cristatus; tuftsThe surfaces of oral streptococci control the adhesive interactions that determine the specific ecologic niche of these bacteria within the oral cavity. It is believed that many of these interactions are associated with appendages that decorate the bacterial surface. Two classes of these structures, fibrils and fimbriae, have been described on different streptococcal species (11). The majority of the streptococci carry short fibrils (40-400 nm), which are thin Copyright clumped structures that may be peritrichous or localized in tufts (8). A few streptococcal strains carry peritrichous fimbriae, with a width of 3-5 nm, which are longer (1-3 μm) and more flexible than fibrils.The structure and function of one peritrichous fibril component on Streptococcus gordonii DL1 has been studied by McNab et al. (17), who showed that the sparse, peritrichous fibrils (61 nm long) are encoded by the cshA gene (18). The CshA polypeptide (259 kDa) contains 2508 amino acid residues and is apparently not glycosylated. The protein comprises a 41-residue amino-terminal signal sequence, a nonrepetitive region, and an extensive 101 amino ac...

A unique serine-rich repeat protein (Srr-2) and novel surface antigen (ε) associated with a virulent lineage of serotype III Streptococcus agalactiae

“…Other streptococcal Srr proteins have been reported to function as adhesins (Wu et al, 1998;Bensing & Sullam, 2002;. Fap1 from Streptococcus parasanguinis (formerly parasanguis) binds to saliva-coated hydroxyapatite (Wu et al, 1998;Wu & Fives-Taylor, 1999), and a Fap1-like protein, SrpA of Streptococcus cristatus, is associated with adhesion to heterologous bacterial species from plaque biofilm (Handley et al, 2005). S. gordonii GspB mediates binding to human platelets (Bensing & Sullam, 2002).…”

StreptococcusAdherence and Colonization

“…However, the CshA polypeptide (259 kDa) produced by S. gordonii has been identified as the structural and functional component of one fibril type (394) ( Table 1). while SrpA has been shown to comprise long (400-nm) fibrils in S. cristatus and to confer coaggregation capabilities (216). Because these fibrillar structures presumably confer a selective advantage to streptococci colonizing the host, perhaps initially by mediating adherence interactions, they are important to consider as potential targets for inhibitors or vaccines.…”

Glycosylation and biogenesis of a family of serine-rich bacterial adhesins

“…The sequencing of the large repetitive region was completed by using a transposon mutagenesis strategy which allows us to sequence one 400-600 bp repetitive region at a time and assemble them manually based on the exact transposition insertion sites (Wu & Fives-Taylor, 1999). The unusual repetitive nature of Fap1 was initially thought to be artificial; however, the discovery of Fap1-like proteins in other streptococci, such as Streptococcus gordonii strains M99 and DL1 (Bensing & Sullam, 2002;Takahashi et al, 2002;Vickerman et al, 2007), Streptococcus cristatus (Handley et al, 2005) and the sequenced genome of Streptococcus pneumoniae TIGR4 (Tettelin et al, 2001), has confirmed our findings and stimulated researchers' interest in the area.…”

“…sanguinis (Xu et al, 2007) and Strep. cristatus (Handley et al, 2005), and in important human pathogens, including Strep. agalactiae (Glaser et al, 2002), Strep.…”