Amiloride at pH 7.0 inhibits the Na +-driven flagellar motors of Vibrio alginolyticus but allows cell growth

Amiloride, a specific inhibitor for the Na +-driven flagellar motors of alkalophilic Bacillus, is known to inhibit secondarily the growth of alkalophiles. The motility of a marine Vibrio, V. alginolyticus, was almost completely inhibited by 2 mM amiloride either at pH 7.0 or 8.5. We found that this concentration of amiloride inhibited the cell growth completely at pH 8.5 but only slightly at pH 7.0. Kinetic analysis of the inhibition of motility by amiloride at pH 7.0 showed that the inhibition was competitive with Na + in the medium. Thus, amiloride at pH 7.0 is really a specific and useful tool for the analysis of the Na +-driven flagellar motors of Vibro.