Bacterial recognition of mineral surfaces: nanoscale interactions between Shewanella and alpha-FeOOH

Force microscopy has been used to quantitatively measure the infinitesimal forces that characterize interactions between Shewanella oneidensis (a dissimilatory metal-reducing bacterium) and goethite (alpha-FeOOH), both commonly found in Earth near-surface environments. Force measurements with subnanonewton resolution were made in real time with living cells under aerobic and anaerobic solutions as a function of the distance, in nanometers, between a cell and the mineral surface. Energy values [in attojoules (10(-18) joules)] derived from these measurements show that the affinity between S. oneidensis and goethite rapidly increases by two to five times under anaerobic conditions in which electron transfer from bacterium to mineral is expected. Specific signatures in the force curves suggest that a 150-kilodalton putative iron reductase is mobilized within the outer membrane of S. oneidensis and specifically interacts with the goethite surface to facilitate the electron transfer process.