GENETIC AND MOLECULAR CHARACTERIZATION OF THE POLAR FLAGELLUM OF VIBRIO-PARAHAEMOLYTICUS

Vibrio parahaemolyticus possesses two alternate flagellar systems adap ted for movement under different circumstances. A single polar flagell um propels the bacterium in liquid (swimming), while multiple lateral flagella move the bacterium over surfaces (swarming). Energy to rotate the polar flagellum is derived from the sodium membrane potential, wh ereas lateral flagella are powered by the proton motive force. Lateral flagella are arranged peritrichously, and the unsheathed filaments ar e polymerized from a single flagellin. The polar flagellum is synthesi zed constitutively, but lateral flagella are produced only under condi tions in which the polar flagellum is not functional, e.g., on surface s. This work initiates characterization of the sheathed, polar flagell um. Four genes encoding flagellins were cloned and found to map in two loci. These genes, as well as three genes encoding proteins resemblin g HAPs (hook-associated proteins), were sequenced. A potential consens us polar flagellar promoter was identified by using upstream sequences from seven polar genes. It resembled the enterobacterial sigma(28) co nsensus promoter. Three of the four flagellin genes were expressed in Escherichia coli, and expression was dependent on the product of the F liA gene encoding sigma(28). The fourth flagellin gene may be differen t regulated. It was not expressed in E. coli, and inspection of upstre am sequence revealed a potential sigma(54) consensus promoter. Mutants with single and multiple defects in flagellin genes were constructed in order to determine assembly rules for filament polymerization, HAP mutants displayed new phenotypes, which were different from those of S almonella typhimurium and most probably were the result of the filamen t being sheathed.