Abstract
Actinomyces oris expresses type 1 and 2 fimbriae on the cell surface. Type 2 fimbriae mediate co-aggregation and biofilm formation and are composed of the shaft fimbrillin FimA and the tip fimbrillin FimB. Short-chain fatty acids (SCFAs) are metabolic products of oral bacteria, but the effects of exogenous SCFAs on FimA-dependent biofilm formation are poorly understood. We performed two types of biofilm formation assays using A. oris MG1 or MG1.ΔfimA to observe the effects of SCFAs on FimA-dependent biofilm formation in 96-well and six-well microtiter plates and a flow cell system. SCFAs did not induce six- and 16-hour biofilm formation of A. oris MG1 and MG1.ΔfimA in saliva-coated 96-well and six-well microtiter plates in which metabolites produced during growth were not excluded. However, 6.25 mM butyric acid and 3.125 mM propionic acid induced FimA-dependent biofilm formation and cell death in a flow cell system in which metabolites produced during growth were excluded. Metabolites produced during growth may lead to disturbing effects of SCFAs on the biofilm formation. The pure effects of SCFAs on biofilm formation were induction of FimA-dependent biofilm formation, but the stress responses from dead cells may regulate its effects. Therefore, SCFA may play a key role in A. oris biofilm formation.
Highlights
The initial attachment of bacteria plays an important role in colonization and interactions with other bacteria on the tooth surface during oral biofilm formation in the human oral cavity [1,2,3,4]
Actinomyces oris, formerly called Actinomyces naeslundii genospecies 2 [5,6], is a well-known early colonizer that interacts with other bacteria in the oral cavity [6,7]
In flow cell systems, 6.25 mM butyric acid and 3.13 mM propionic acid promoted dead cells in FimA-dependent biofilm formation and increased attached and aggregated dead cells. These results indicate that Short-chain fatty acids (SCFAs) from other oral bacteria, such P. gingivalis and F. nucleatum, stimulated FimA-dependent biofilm formation of A. oris, which is involved in stress responses
Summary
The initial attachment of bacteria plays an important role in colonization and interactions with other bacteria on the tooth surface during oral biofilm formation in the human oral cavity [1,2,3,4]. Actinomyces oris, formerly called Actinomyces naeslundii genospecies 2 [5,6], is a well-known early colonizer that interacts with other bacteria in the oral cavity [6,7]. Fructosyltransferases (FTFs) of A. naeslundii synthesize levan, which contributes to cell-cell communication in biofilm formation, but not initial attachment [8]. Levan is an important factor that induces biological activities. A. oris induces co-aggregation with Streptococcus gordonii and Streptococcus sanguinis as early colonizers and Fusobacterium nucleatum as middle colonizers in oral biofilms [1]
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