Biofilm behavior of Tannerella forsythia strains and S-layer glycosylation mutants

The periodontopathogen Tannerella forsythia has a characteristic cell surface (S-) layer modified with a unique O-glycan. This structure was analyzed for its role in biofilm formation employing an in vitro multispecies biofilm model, into which different T. forsythia strains and mutants with a modified cell surface composition were incorporated together with nine other oral species. The influence of the glycosylated T. forsythia S-layer on the bacterial composition of the biofilms was analyzed quantitatively using quantitative real-time PCR as well as qualitatively by fluorescence in situ hybridization and confocal laser scanning microscopy. It was evident that while changes of the T. forsythia cell surface did not affect the quantitative composition of the multispecies consortium, with the exception of Campylobacter rectus cell numbers, the localization of T. forsythia within the biofilm and its aggregation with Porphyromonas gingivalis were changed. Thus, the glycosylated T. forsythia S-layer might have relevance for positioning of this species within the biofilm and influence its co-localization with P. gingivalis and the prevalence of C. rectus. This might further pinpoint a pivotal role of T. forsythia cell surface structures in the virulence of this species when interacting with host tissues and immune system, from within or beyond the biofilm.