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BioMed Research International
Volume 2015 (2015), Article ID 608682, 11 pages
Research Article

Expression of the Genes Encoding the Trk and Kdp Potassium Transport Systems of Mycobacterium tuberculosis during Growth In Vitro

1Department of Immunology, Faculty of Health Sciences, University of Pretoria, Pretoria 0001, South Africa
2Department of Genetics, Faculty of Natural and Agricultural Sciences, University of Pretoria, Pretoria 0001, South Africa

Received 19 May 2015; Revised 30 July 2015; Accepted 2 August 2015

Academic Editor: Bo Zuo

Copyright © 2015 Moloko C. Cholo et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Two potassium (K+)-uptake systems, Trk and Kdp, are operative in Mycobacterium tuberculosis (Mtb), but the environmental factors triggering their expression have not been determined. The current study has evaluated the expression of these genes in the Mtb wild-type and a trk-gene knockout strain at various stages of logarithmic growth in relation to extracellular K+ concentrations and pH. In both strains, mRNA levels of the K+-uptake encoding genes were relatively low compared to those of the housekeeping gene, sigA, at the early- and mid-log phases, increasing during late-log. Increased gene expression coincided with decreased K+ uptake in the context of a drop in extracellular pH and sustained high extracellular K+ concentrations. In an additional series of experiments, the pH of the growth medium was manipulated by the addition of 1N HCl/NaOH. Decreasing the pH resulted in reductions in both membrane potential and K+ uptake in the setting of significant induction of genes encoding both K+ transporters. These observations are consistent with induction of the genes encoding the active K+ transporters of Mtb as a strategy to compensate for loss of membrane potential-driven uptake of K+ at low extracellular pH. Induction of these genes may promote survival in the acidic environments of the intracellular vacuole and granuloma.