Abstract
SummaryAs a member of subgingival multispecies biofilms, Tannerella forsythia is commonly associated with periodontitis. The bacterium has a characteristic cell surface (S‐) layer modified with a unique O‐glycan. Both the S‐layer and the O‐glycan were analyzed in this study for their role in biofilm formation by employing an in vitro multispecies biofilm model mimicking the situation in the oral cavity. Different T. forsythia strains and mutants with characterized defects in cell surface composition were incorporated into the model, together with nine species of select oral bacteria. The influence of the T. forsythia S‐layer and attached glycan on the bacterial composition of the biofilms was analyzed quantitatively using colony‐forming unit counts and quantitative real‐time polymerase chain reaction, as well as qualitatively by fluorescence in situ hybridization and confocal laser scanning microscopy. This revealed that changes in 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 bacterial agglomeration varied depending on changes in the S‐layer glycan, and this also affected its aggregation with Porphyromonas gingivalis. This suggests a selective role for the glycosylated T. forsythia S‐layer in the positioning of this species within the biofilm, its co‐localization with P. gingivalis, and the prevalence of C. rectus. These findings might translate into a potential role of T. forsythia cell surface structures in the virulence of this species when interacting with host tissues and the immune system, from within or beyond the biofilm.
Highlights
In order to proliferate and persist in their habitat, bacteria tend to live predominately in biofilms, which are highly complex and dynamic, polymicrobial communities providing protection from shear forces and host immune responses [1]
We recently found evidence that the T. forsythia ATCC 43037 wild-type strain carries a modified pseudaminic acid (Pse) residue as a terminal constituent of the S-layer O-glycan [26], while in the clinical isolate T. forsythia UB4, this residue is present as its stereoisomer, legionaminic acid (Leg) [39] (Table 1, Fig. S1)
Forsythia UB4 ∆legC on a mucin-coated surface [39] and that T. forsythia ATCC 43037 ∆wecC
Summary
In order to proliferate and persist in their habitat, bacteria tend to live predominately in biofilms, which are highly complex and dynamic, polymicrobial communities providing protection from shear forces and host immune responses [1]. The oral bacteria exist in a natural balance with their host. Different factors such as smoking, diabetes, genetic predisposition or poor dental hygiene can cause the community to become dysbiotic [3, 4], enabling potentially pathogenic bacteria to increase in numbers and cause persistent infections, such as periodontitis. Gram-negative anaerobes; among those are the periodontal pathogens Porphyromonas gingivalis, Treponema denticola and Tannerella forsythia [5].
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