Streptococcus Gordonii as a Developmental Driver of a Polymicrobial Community
Objectives: Streptococcus gordonii is a pioneer colonizer of the oral cavity. Many S. gordonii surface proteins are processed by sortase A (SrtA) to mediate adherence to body surfaces. We sought to determine whether WT and ΔSrtA S. gordonii strains affect community development of a supragingival plaque microcosm.
Methods: S. gordonii, Actinomyces naeslundii, Corynebacterium matruchotii, Neisseria mucosa, Rothia dentocariosa and ΔSrtA S gordonii strains were grown overnight in BHI and washed for coaggregation assays or inoculated together at equal OD600nm for growth in SHI media in 96-well plates. Biofilm biomass was determined by staining with 0.1% (w/v) crystal violet. Biofilm community composition was determined by washing and resuspending cells in PBS with 50mM L-arginine to assist with cell dispersion, then plating on blood agar for enumeration of colonial morphotypes. Interspecies coaggregation was quantified by combining equal volumes S. gordonii cells with a community partner in buffer and comparing OD600nm before and after coaggregation.
Results: The ΔSrtA polymicrobial community biomass tended to be lower than the WT community. When formed with WT or S. gordonii ΔSrtA, community composition differed as a percentage of each species. The eventual community composition is not apparently reflected by coaggregation patterns between community members and either strain of S. gordonii.
Conclusions: Biofilm communities formed in the presence of WT and S. gordonii ΔSrtA strains persisted to 72 hrs. The community composition was not reflected by coaggregation with WT or ΔSrtA S. gordonii and community members. Given the overall similarities in communities formed in the presence of WT and S. gordonii ΔSrtA, lipoprotein adhesins are likely being upregulated to compensate for the loss of LPXTG-motif surface proteins. We speculate that the presence of saliva will substantially modify the development of communities formed by this supragingival plaque microcosm.