Directed polar secretion of protease from single cells of Vibrio cholerae via the type II secretion pathway

Bacteria have long been thought of as little more than sacks of homogeneous ly distributed enzymes. However, recent cytological studies indicate that b acteria are compartmentalized with proteins involved in processes such as c ell division, motility, chemotaxis, and development located at distinct sit es. We have used the green fluorescent protein as a reporter to determine t he cellular distribution of the extracellular protein secretion (eps)-encod ed type II secretion complex responsible for extracellular secretion of cho lera toxin and hemagglutinin/protease in Vibrio cholerae. Real-time monitor ing of green fluorescent protein fused to EpsM in living cells indicated th at, like the single polar flagellum, the Eps complex is located at the old pole after cell division. Eps-dependent protease secretion was also visuali zed in single cells by fluorescence microscopy by using intramolecularly qu enched casein. This analysis demonstrated that active protease secretion is focused at the poles and colocalizes with the site of the polar Eps appara tus. These results suggest that the type II secretion complex is responsibl e for directed delivery of virulence factors during cholera pathogenesis.