Adhesion of dissimilatory Fe(III)-reducing bacteria to Fe(III) minerals

The metabolism of dissimilatory iron-reducing bacteria (DIRB) may provide a means of remediating contaminated subsurface soils. The factors controlling the rate and extent of bacterial F(III) mineral reduction are poorly understood. Recent research suggests that molecular-scale interactions between DIRB cells and Fe( III) mineral particles play an important role in this process. One of these interactions, cell adhesion to Fe( III) mineral particles, appears to be a complex process that is, at least in part, mediated by a variety of surface proteins. This study examined the hypothesis that the flagellum serves as an adhesin to different Fe( III) minerals that range in their surface area and degree of crystallinity. Deflagellated cells of the DIRB Shewanella algae BrY showed a reduced ability to adhere to hydrous ferric oxide (HFO) relative to flagellated cells. Flagellated cells were also more hydrophobic than deflagellated cells. This was significant because hydrophobic interactions have been previously shown to dominate S. algae cell adhesion to Fe(III) minerals. Pre-incubating HFO, goethite, or hematite with purified flagella inhibited the adhesion of S. algae BrY cells to these minerals. Transposon mutagenesis was used to generate a flagellum-deficient mutant designated S. algae strain NF. There was a significant difference in the rate and extent of S. algae NF adhesion to HFO, goethite, and hematite relative to that of S. algae BrY. Amiloride, a specific inhibitor of Na+-driven flagellar motors, inhibited S. algae BrY motility but did not affect the adhesion of S. algae BrY to HFO. S. algae NF reduced HFO at the same rate as S. algae BrY. Collectively, the results of this study support the hypothesis that flagellum-mediated adhesion is not requisite for Fe(III) mineral reduction.