Flagellin is the subunit protein which polymerizes to form the filaments of bacterial flagella. Essential for lateral flagellar synthesis and swarming motility. Homomer. V.parahaemolyticus possesses two flagellar systems: a single polar flagellum propels the bacterium in liquid (swimming), while multiple lateral (peritrichous) flagella move the bacterium over surfaces (swarming). The polar flagellum is synthesized constitutively but lateral flagella are produced only under conditions in which the polar flagellum is not functional. The peritrichous flagella are unsheathed and powered by the proton motive force. Belongs to the bacterial flagellin family.