Sodium Energetic Cycle in the Natronophilic Bacterium Thioalkalivibrio versutus .

As inhabitants of soda lakes, Thioalkalivibrio versutus are halo- and alkaliphilic bacteria that have previously been shown to respire with the first demonstrated Na + -translocating cytochrome- c oxidase (CO). The enzyme generates a sodium-motive force (Δ s ) as high as -270 mV across the bacterial plasma membrane. However, in these bacteria, operation of the possible Δ s consumers has not been proven. We obtained motile cells and used them to study the supposed Na + energetic cycle in these bacteria. The resulting motility was activated in the presence of the protonophore 2-heptyl-4-hydroxyquinoline N-oxide (HQNO), in line with the same effect on cell respiration, and was fully blocked by amiloride-an inhibitor of Na + -motive flagella. In immotile starving bacteria, ascorbate triggered CO-mediated respiration and motility, both showing the same dependence on sodium concentration. We concluded that, in T. versutus , Na + -translocating CO and Na + -motive flagella operate in the Na + energetic cycle mode. Our research may shed light on the energetic reason for how these bacteria are confined to a narrow chemocline zone and thrive in the extreme conditions of soda lakes.