The A domain of clonal complex 1-type fibronectin binding protein B promotes adherence and biofilm formation in Staphylococcus aureus

Adhesive interactions between Staphylococcus aureus and the host rely on cell-wall-anchored proteins such as fibronectin-binding protein B (FnBPB). Recently we showed that the FnBPB protein expressed by clonal complex (CC) 1 isolates of S. aureus mediates bacterial adhesion to corneodesmosin. The proposed ligand-binding region of CC1-type FnBPB shares just 60 % amino acid identity with the archetypal FnBPB protein from CC8. Here we investigated ligand binding and biofilm formation by CC1-type FnBPB. We found that the A domain of FnBPB binds to fibrinogen and corneodesmosin and identified residues within the hydrophobic ligand trench in the A domain that are essential for the binding of CC1-type FnBPB to ligands and during biofilm formation. We further investigated the interplay between different ligands and the influence of ligand binding on biofilm formation. Overall, our study provides new insights into the requirements for CC1-type FnBPB-mediated adhesion to host proteins and FnBPB-mediated biofilm formation in S. aureus.