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 034) chromosome that contained two additional polar stator genes, named pom[A.sub.2] and pom[B.sub.2]. A. hydrophila Pom[A.sub.2] and Pom[B.sub.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 pom[A.sub.2][B.sub.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 Pom[A.sub.2][B.sub.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 Pom[A.sub.2][B.sub.2] are sodium.coupled stator complexes, although Pom[A.sub.2][B.sub.2] is more sensitive to low concentrations of sodium than PomAB. Furthermore, the level of transcription in aqueous and high-viscosity environments of pom[A.sub.2][B.sub.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 Pom[A.sub.2][B.sub.2]) are found.