Two Redundant Sodium-Driven Stator Motor Proteins Are Involved in Aeromonas hydrophila Polar Flagellum Rotation

Motility is an essential characteristic for mesophilic Aeromonas strains. We identified a new polar flagellum region (region 6) in the A. hydrophila AH-3 (serotype O34) chromosome that contained two additional polar stator genes, named pomA(2) and pomB(2). A. hydrophila PomA(2) and PomB(2) are highly homologous to other sodium-conducting polar flagellum stator motors as well as to the previously described A. hydrophila AH-3 PomA and PomB. pomAB and pomA(2)B(2) were present in all the mesophilic Aeromonas strains tested and were independent of the strains' ability to produce lateral flagella. Unlike MotX, which is a stator protein that is essential for polar flagellum rotation, here we demonstrate that PomAB and PomA(2)B(2) are redundant sets of proteins, as neither set on its own is essential for polar flagellum motility in either aqueous or high-viscosity environments. Both PomAB and PomA(2)B(2) are sodium-coupled stator complexes, although PomA(2)B(2) is more sensitive to low concentrations of sodium than PomAB. Furthermore, the level of transcription in aqueous and high-viscosity environments of pomA(2)B(2) is reduced compared to that of pomAB. The A. hydrophila AH-3 polar flagellum is the first case described in which two redundant sodium-driven stator motor proteins (PomAB and PomA(2)B(2)) are found.