Morphology of YB3558 and YB3559. Phase micrographs of exponentially growing cultures of CB15, YB3558, ctrA401 and YB3559 at 30°C. YB3558 displays increased filamentation, increased percentage of cells with multiple constrictions, and a stalkless phenotype. These defects are also seen in the ctrA temperature sensitive strain grown under permissive conditions. Complementation of YB3558 with a wild-type ctrA gene under native control (YB3559) restores cell morphology to that of wild-type.