Characterization of Fusobacterium nucleatum ATCC 23726 adhesins involved in strain-specific attachment to Porphyromonas gingivalis

Bacterial adherence is an essential virulence factor in pathogenesis and infection. Fusobacterium nucleatum has a central role in oral biofilm architecture by acting as a bridge between early Gram-positive and late Gram-negative colonizers that do not otherwise adhere to each other. In this study, we survey a key adherence interaction of F. nucleatum with Porphyromonas gingivalis, and present evidence that multiple fusobacterial adhesins have a role in the attachment of F. nucleatum ATCC 23726 to P. gingivalis in a highly strain-dependent manner. Interaction between these species displayed varying sensitivities to arginine, galactose and lactose. Arginine was found to hamper coaggregation by at least 62% and up to 89% with several P. gingivalis strains and galactose inhibition ranged from no inhibition up to 58% with the same P. gingivalis strains. Lactose consistently inhibited F. nucleatum interaction with these P. gingivalis strains ranging from 40% to 56% decrease in coaggregation. Among the adhesins involved are the previously described Fap2 and surprisingly, RadD, which was described in an earlier study for its function in attachment of F. nucleatum to Gram-positive species. We also provide evidence for the presence of at least one additional adhesin that is sensitive to arginine but unlike Fap2 and RadD, is not a member of the autotransporter family type of fusobacterial large outer membrane proteins. The strain-specific binding profile of multiple fusobacterial adhesins to P. gingivalis highlights the heterogeneity and complexity of interspecies interactions in the oral cavity. Different strains of pathogenic bacteria rely on distinct interactions to anchor themselves firmly into oral ‘biofilm’ communities. The microbe Fusobacterium nucleatum is a major component of these densely populated bacterial societies. This species is not harmful, but can mediate recruitment of disease-causing Porphyromonas gingivalis bacteria into biofilms. Renate Lux and colleagues at the University of California at Los Angeles have demonstrated that various strains of P. gingivalis apparently latch onto different proteins on the surface of F. nucleatum. Previous studiesidentified the protein Fap2 as a binding target for P. gingivalis, but Lux and colleagues found at least one strain that relies on a different protein and found evidence for other as yet unidentified protein ‘anchors’. Identifying the proteins recognized by the most virulent P. gingivalis strains could lead to therapeutics that selectively block these interactions.