Bacterial galvanotropism: mechanisms and applications.

Galvanotropism is the process by which a cell alters its shape to grow directionally in response to an electric field. This phenomenon is known for a wide variety of eukaryotic cells but the first report of bacterial galvanotropism appeared only recently. Escherichia coli, Enterobacter cloacae and (to a lesser extent) Bacillus subtilis curve rapidly and reversibly towards the anode of a uniform electric field. The mechanism for the response is not known but two observations permit a degree of speculation. Firstly, the anode-facing ends of cells elongate more rapidly than the cathode-facing ends of the same cells, suggesting that the field affects regional rates of wall synthesis and degradation. Secondly, the magnitude of the response depends on the extracellular pH, implicating anodal electrophoresis of membrane proteins in the mechanism. The ability of a field to modulate rates of wall growth locally can be exploited to investigate at least two fundamental, yet intractable, questions: the mechanism by which bacteria maintain non-spherical shapes and grow without bursting and the mechanism for the uniform segregation of DNA into daughter cells. Additionally, use of molecular biological techniques may permit identification of the molecular basis for galvanotropism, an approach that has not been feasible for most galvanotropic eukaryotic cells.