Requirements for conversion of the Na+-driven flagellar motor of Vibrio cholerae to the H+-driven motor of Escherichia coli

Bacterial flagella are powered by a motor that converts a transmembrane ele ctrochemical potential of either H+ or Na+ into mechanical work. In Escheri chia coli, the MotA and MotB proteins form the stator and function in proto n translocation, whereas the FliG protein is located on the rotor and is in volved in flagellar assembly and torque generation. The sodium-driven polar flagella of Vibrio species contain homologs of MotA and MotB, called PomA and PomB, and also contain to other membrane proteins called MotX and MotY, which are essential for motor rotation and that might also function in ion conduction. Deletions in pomA, pomB, motX, or motY in Vibrio cholerae resu lted in a nonmotile phenotype, whereas deletion of fliG gave a nonflagellat e phenotype. fliG genes on plasmids complemented fliG-null strains of the p arent species but not fliG-null strains of the other species. FliG-null str ains were complemented by chimeric FliG proteins in which the C-terminal do main came from the other species, however, implying that the C-terminal par t of FliG can function in conjunction with the ion- translocating component s of either species. A V. cholerae strain deleted of pomA, pomB, motX, and motY became weakly motile when the E. coli motA and motB genes were introdu ced on a plasmid. Like E. coli, but unlike wild-type V. cholerae, motility of some V. cholerae strains containing the hybrid motor was inhibited by th e protonophore carbonyl cyanide m-chlorophenylhydrazone under neutral as we ll as alkaline conditions but not by the sodium motor-specific inhibitor ph enamil. We conclude that the E. coli proton motor components MotA and MotB can function in place of the motor proteins of V. cholerae and that the hyb rid motors are driven by the proton motive force.