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

Abstract

<b>:</b> 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 <i>rapA</i> and <i>rapB</i> 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 <i>fad-I</i>, <i>rapA</i><i>,</i> and <i>rapB</i> in interspecies interaction and biofilm formation. Gene inactivation mutants were generated for each of these genes in the <i>nucleatum</i> and <i>polymorphum</i> subspecies of <i>Fusobacterium</i> <i>nucleatum</i> and characterized for their adherence to partner species, biofilm formation, and operon transcription. Binding to <i>Streptococcus</i> <i>gordonii</i> was increased in all mutant strains with Δ<i>fad</i><i>-I</i> having the most significant effect. This increased adherence was directly proportional to elevated <i>radD</i> transcript levels and resulted in significantly different architecture and height of the biofilms formed by Δ<i>fad</i><i>-I</i> and <i>S.</i> <i>gordonii</i> 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.