Lipoteichoic Acid’s Role in Streptococcus gordonii Adhesion

Objectives: For many microbes, attachment is key to their survival. Streptococcus gordonii, an initial colonizer of the oral cavity, needs to attach to oral surfaces to survive. Surface attachment is commonly mediated by cell-wall anchored adhesive proteins known as adhesions. A common component of the Gram-positive cell wall, lipoteichoic acid (LTA) is a polymer that plays an important role in the surface protein biogenesis. Thus, we hypothesized that LTA plays an important role in the adhesion to surfaces and other organisms.
Methods: The LTA-deficient mutant was constructed by allelic replacement of the gene that encodes the enzyme LTA synthase (ltaS). To determine how membrane and cell wall proteins are affected by ltaS deletion, a gel was performed comparing WT and ltaS mutant. LTA’s impact on adhesion was assessed by biofilm formation, coaggregation, and attachment to eukaryotic cells. Biofilm assays were performed on saliva-coated 96 well plates and the biomass was assessed by crystal violet retention. Coaggregation was performed by mixing equal number of S. gordonii with F. nucleatum. Immortalized oral keratinocytes were used to assess adherence to eukaryotic cells. Bacteria strains were added to a 24 well plate containing oral keratinocytes and incubated for attachment.
Results: Cell wall protein expression differed between WT and the ltaS mutant. The cell membrane, however, showed similar protein expression between the WT and the ltaS strain. Biofilm formation of the ltaS mutant was significantly less dense in comparison to the WT. The ltaS mutant also showed defects in adhesion to oral keratinocytes. No defect in coaggregation with F. nucleatum, was observed.
Conclusions: LTA is important in surface protein expression, affecting S. gordonii adherence to oral keratinocytes and biofilm formation. However, no defect was observed in the interaction with other bacterial species, suggesting different interaction mechanisms are used for the interaction with oral keratinocytes and other bacterial species.