Role of FAD-I in Fusobacterial Interspecies Interaction and Biofilm Formation.

RadD, a major adhesin of oral fusobacteria, is part of a four-gene operon encoding the small lipoprotein FAD-I and two currently uncharacterized small proteins encoded by the and genes. Previously, we described a role for FAD-I in the induction of human B-defensin 2 (hBD2) upon contact with oral epithelial cells. Here, we investigated potential roles for , and in interspecies interaction and biofilm formation. Gene inactivation mutants were generated for each of these genes in the and subspecies of and characterized for their adherence to partner species, biofilm formation, and operon transcription. Binding to was increased in all mutant strains with Δ having the most significant effect. This increased adherence was directly proportional to elevated transcript levels and resulted in significantly different architecture and height of the biofilms formed by Δ and compared to the wild-type parent. In conclusion, FAD-I is important for fusobacterial interspecies interaction as its lack leads to increased production of the RadD adhesin suggesting a role of FAD-I in its regulation. This regulatory effect does not require the presence of functional RadD.