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 diss imilatory metal-reducing bacterium) and goethite (alpha -FeOOH), both commo nly found in Earth near-surface environments. Force measurements with subna no-newton resolution were made in real time with living cells under aerobic and anaerobic solutions as a function of the distance, in nanometers, betw een a cell and the mineral surface. Energy values [in attojoules (10(-18) j oules)] derived from these measurements show that the affinity between S. o neidensis and goethite rapidly increases by two to five times under anaerob ic conditions in which electron transfer from bacterium to mineral is expec ted. Specific signatures in the force curves suggest that a 150-kilodalton putative iron reductase is mobilized within the outer membrane of S. oneide nsis and specifically interacts with the goethite surface to facilitate the electron transfer process.