Although saliva is widely recognized as the primary source of carbon and nitrogen for growth of the dental plaque biofilm community, little is known about how different oral bacteria utilize specific salivary components. To address this question, 32 strains representing 16 genera commonly isolated from early plaque biofilms were compared for growth in secondary cultures of whole saliva that was stabilized by heat-treatment and subsequent dialysis. Cell densities measured by qPCR ranged from 1x106 to 1x107/ml for strains of Streptococcus gordonii, S. oralis, S. mitis and one strain of S. sanguinis and from 1x105 to 1x106/ml for strains of S. mutans, Gemella haemolysans and Granulicatella adiacens. In contrast, little or no growth was noted for three other strains of S. sanguinis or for strains of S. salivarius, S. vestibularis, S. sobrinus, Actinomyces spp., Abiotrophia defectiva and Rothia dentocariosa. SDS PAGE, 2-D electrophoresis and lectin blotting of saliva from cultures of S. gordonii, S. oralis and S. mitis revealed species-specific differences in degradation of basic proline-rich glycoproteins. In contrast, saliva cultures of other bacteria were indistinguishable from control saliva. Differences in growth and salivary glycan foraging between oral species have important implications for dental plaque biofilm development. Growth of the oral commensal Streptococcus gordonii in saliva may depend on a number of glycoside hydrolases (GHs) including three cell wall-anchored proteins that are homologs of pneumococcal -galactosidase (BgaA), -N-acetylglucosaminidase (StrH) and endohexosaminidase D (EndoD). To test this hypothesis, we introduced unmarked in-frame deletions in the corresponding genes of S. gordonii DL1, verified the presence (or absence) of encoded proteins on the resulting mutant strains and compared these strains with wild type DL1 for growth and glycan foraging in saliva. Overnight growth of wild type DL1 was reduced 3- to 10-fold by deletion of any one or two genes and approximately 20-fold by deletion of all three genes. The only notable change in the salivary proteome associated with this reduction of growth was a downward shift in the apparent molecular weight of basic proline-rich glycoproteins (PRG), which was accompanied by the loss of lectin binding sites for galactose-specific Erythrina cristagalli agglutinin (ECA) and mannose-specific Galanthus nivalis agglutinin (GNA). Binding of ECA to PRG was also abolished in saliva cultures of mutants that expressed cell-surface BgaA alone or together with either StrH or EndoD. However, the subsequent loss of GNA binding was only seen in saliva co-cultures of different mutants that together, expressed all three cell-surface GHs. The findings indicate that growth of S. gordonii DL1 in saliva depends to a significant extent on the sequential actions of BgaA followed by StrH and EndoD on N-linked glycans of PRG. Molecular taxonomic surveys of healthy individuals have shown that an overall paradigm oral community exists at the genus level, yet subject-dependent deviations can be large. The interbacterial cell-cell binding phenotype known as coaggregation is important to oral biofilm initiation, but limited data exist on organisms other than streptococci and actinomyces, and little is known about distribution of the phenotype between individuals. To address this problem, biofilm communities formed intra-orally on enamel substrata in two healthy individuals are described using molecular taxonomy (HOMIM microarray) and subject-specific culture collections. Subject-dependent differences in community composition documented by both approaches were congruent. Coaggregation profiles of the isolates were likewise subject-specific. For both individuals, strains of Rothia and Haemophilus demonstrated extensive coaggregation with co-isolated bacteria; confocal microscopy of undisturbed biofilms demonstrated these genera to be tightly integrated within the biofilm. Additionally, a previously uncultivated streptococcal phylotype and a new coaggregation phenotype were isolated. Together, the data demonstrate that coaggregation phenotypes within individuals communities can differ extensively, and that genera other than streptococci and actinomyces undergo widespread coaggregation interactions. Thus cell-cell recognition is central to oral biofilm formation, yet its characteristics differ at the level of single individuals.
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