Protein-mediated adhesion of the dissimilatory Fe(III)-reducing bacterium Shewanella alga BrY to hydrous ferric oxide

The rate and extent of bacterial Fe(III) mineral reduction are governed by molecular-scale interactions between the bacterial cell surface and the min eral surface. These interactions are poorly understood. This study examined the role of surface proteins in the adhesion of Shewanella alga BrY to hyd rous ferric oxide (HFO), Enzymatic degradation of cell surface polysacchari des had no effect on cell adhesion to HFO, The proteolytic enzymes Streptom yces griseus protease and chymotrypsin inhibited the adhesion of S. alga Br Y cells to HFO through catalytic degradation of surface proteins. Trypsin i nhibited S, alga BrY adhesion solely through surface-coating effects. Prote ase and chymotrypsin also mediated desorption of adhered S, alga BrY cells from HFO while trypsin did not mediate cell desorption. Protease removed a single peptide band that represented a protein with an apparent molecular m ass of 50 kDa, Chymotrypsin removed two peptide bands that represented prot eins with apparent molecular masses of 60 and 31 kDa. These proteins repres ent putative HFO adhesion molecules, S, alga BrY adhesion was inhibited by up to 46% when cells were cultured at sub-MICs of chloramphenicol, suggesti ng that protein synthesis is necessary for adhesion. Proteins extracted fro m the surface of S, alga BrY cells inhibited adhesion to HFO by up to 41%, A number of these proteins bound specifically to HFO, suggesting that a com plex system of surface proteins mediates S. alga BrY adhesion to HFO.