title: Presence of a nonmetabolizable solute that is translocated with Na+ enhances Na+-dependent pH homeostasis in an alkalophilic Bacillus.
abstract: The presence of a nonmetabolizable solute whose uptake is coupled to the inward translocation of Na+ has been found to enhance Na+-dependent pH homeostasis and survival of an obligately alkalophilic bacterium. Upon shift of cells of Bacillus firmus RAB from growth medium to buffers at pH 10.5, viability and maintenance of a relatively acidified cytoplasm depended upon the presence of Na+ and was augmented by the inclusion of alpha-aminoisobutyric acid in the buffer. Similarly, when cells were first equilibrated at pH 8.5 and then shifted to buffer at pH 10.5, an extraordinary capacity to maintain a relatively low pHin was exhibited, but only in the presence of Na+. In this protocol, the inclusion of alpha-aminoisobutyric acid actually resulted in an early overshoot of proton influx and also rendered a suboptimal concentration of Na+ efficacious in pH homeostasis. When a protonophoric uncoupler was added to the equilibration and shift buffers, Na+-dependent acidification of the interior was inhibited at early time points. The results support the conclusion drawn from earlier work that a Na+/H+ antiporter plays a critical role in pH homeostasis in the obligately alkalophilic bacilli. Moreover, the current findings indicate that the Na+/solute symporters are a physiologically functional pathway for completing the sodium cycle that controls pHin.
mesh_terms: D000621:Aminoisobutyric Acids / Q000378:metabolism; D001407:Bacillus / Q000378:metabolism*; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D006706:Homeostasis; D006863:Hydrogen-Ion Concentration; D012964:Sodium / Q000378:metabolism*; D012996:Solutions
chemical_list: D000621:Aminoisobutyric Acids; D012996:Solutions; C100049:2-aminoisobutyric acid; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D012964:Sodium