Directed natural forces of affinity between a bacterium and mineral

The formation of a bond between a bacterium and a mineral is ultimately controlled by forces that operate over length scales of a few nanometers. This manuscript presents evidence that bacteria may actively modulate forces at the cell-mineral interface to promote contact with specific mineral phases. Nano- to pico-Newton forces were measured between goethite (FeOOH) and each of two species of Gram negative bacteria (Escherichia coli and Shewanella oneidensis) in aqueous solution of varying oxygen concentration. The interactions were dominated by electrostatic and steric forces as either bacterium approached to within 10 to 12 nm of the surface of goethite. The van der Waals force exhibited an influence on each bacterium-mineral pair at separations of ∼2 nm. These types of nonspecific forces were all that were observed for the E. coli-goethite pair. However, S. oneidensis exhibited a selective disposition to form a specific bond with goethite, particularly under anaerobic conditions. These data suggest that S. oneidensis is able to perceive and recognize the surface of metal oxyhydroxides and regulate attractive forces at the cell-oxide interface. This may be a vestige of the close evolutionary linkage between iron oxyhydroxides and metal-reducing bacteria like Shewanella, which can use Fe(III) in the crystal structure of a mineral as a terminal electron acceptor.