FIG. 2.

Chemotaxis to AQDS in a plug plate assay. Darker areas represent the location of the reduced form of AQDS, AHDS, which is orange in color. (a) Location of AHDS both in and around the plug under anaerobic conditions. (b) Location of AHDS after briefly exposing the plate to aerobic conditions. A brief exposure to aerobic conditions causes reoxidation of the AHDS. This reoxidation occurs faster where no cells are present. The arrow denotes the location of the cells that have accumulated around the agar plug.