Departmental Papers (Dental)

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Journal Article

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Oral Microbiology and Immunology





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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.

Copyright/Permission Statement

This is the peer reviewed version of the following article: [Handley, P.S., Correia, F.F., Russell, K., Rosan, B., DiRienzo, J.M. (2005 ). Association of a novel high molecular weight, serine-rich protein (SrpA) with fibril-mediated adhesion of the oral biofilm bacterium Streptococcus cristatus. Molecular Oral Microbiology;20(3):131-40.]. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions.


corncobs, fibrils, SrpA, Streptococcus cristatus, tufts

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Dentistry Commons



Date Posted: 01 March 2022

This document has been peer reviewed.