Growth Assays of Vibrio cholerae Membrane Transporter Mutants in Different pH and Cation Conditions

Vibrio cholerae achieves survival in various saline environments by a network of different Na+ dependent transporters, antiporters, and symporters. The most important transporters for sodium homeostasis are the sodium-translocating NADH-ubiquinone oxidoreductase (VC-NQR) and the secondary sodium pumps Vc-NhaA and Vc-NhaB. It has been difficult to tease out the metabolic role of Vc-NQR as deletion of this dominant contributor to aerobic respiration causes distorting growth defects. By adding L-lactate, we were able to overcome the basic growth defect of a Vc-NQR mutant [1]. Here, we report the growth characteristics of various single and double mutants of V. cholerae lacking these transporters in regards to cation resistance in different pH environments, in presence and absence of L-lactate. Overall, Vc-NhaA appears to be instrumental for sodium transport at pH 7.5 and 8.5 and lithium at pH 7.5 in concert with Vc-NQR, and essential at lithium concentrations of 75 mM and higher at pH 8.5 independent of Vc-NQR. In addition, there is some evidence that Vc-NhaA is able to transport potassium at high pH and under high potassium pressure.