ZomB is essential for chemotaxis of Vibrio alginolyticus by the rotational direction control of the polar flagellar motor

Bacteria exhibit chemotaxis by controlling flagellar rotation to move toward preferred places or away from nonpreferred places. The change in rotation is triggered by the binding of the chemotaxis signaling protein CheY-phosphate (CheY-P) to the C-ring in the flagellar motor. Some specific bacteria, including Vibrio spp. and Shewanella spp., have a single transmembrane protein called ZomB. ZomB is essential for controlling the flagellar rotational direction in Shewanella putrefaciens and Vibrio parahaemolyticus. In this study, we confirmed that the zomB deletion results only in the counterclockwise (CCW) rotation of the motor in Vibrio alginolyticus as previously reported in other bacteria. We found that ZomB is not required for a clockwise-locked phenotype caused by mutations in fliG and fliM, and that ZomB is essential for CW rotation induced by overproduction of CheY-P. Purified ZomB proteins form multimers, suggesting that ZomB may function as a homo-oligomer. These observations imply that ZomB interacts with protein(s) involved in either flagellar motor rotation, chemotaxis, or both. We provide the evidence that ZomB is a new player in chemotaxis and is required for the rotational control in addition to CheY in Vibrio alginolyticus.