The Physiological Role of Two Sodium Channels MotPS and Na_VBP of Alkaliphilic Bacillus

Abstract

In alkaliphilic Bacillus, Na⁺-dependent pH homeostasis involves antiport activities as well as Na⁺ re-entry routes. MotPS that are homologous to MotAB are required for the Na⁺-dependent motility of alkaliphilic B. pseudofirmus OF4. Purified and reconstituted MotPS support amiloride analogue-sensitive Na⁺ flux. Mutants lacking functional MotPS display no deficit in pH homeostasis in pH shift experiments conducted with sub-optimal added [Na⁺] in the absence of solutes whose uptake is coupled to Na⁺ re-entry. By contrast, a role was evident for the recently described NaChBac (voltage-dependent) Na⁺ channel at sub-optimal [Na⁺]. NaChBac mutants exhibit a significant loss of pH homeostasis capacity.