Expression of the Genes Encoding the Trk and Kdp Potassium Transport Systems of Mycobacterium tuberculosis during Growth In Vitro.
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.
Department of Immunology, Faculty of Health Sciences, University of Pretoria, Pretoria 0001, South Africa.
Moloko C
MC
Cholo
Department of Genetics, Faculty of Natural and Agricultural Sciences, University of Pretoria, Pretoria 0001, South Africa.
Elizabeth J
EJ
van Rensburg
Department of Immunology, Faculty of Health Sciences, University of Pretoria, Pretoria 0001, South Africa.
Ayman G
AG
Osman
Department of Immunology, Faculty of Health Sciences, University of Pretoria, Pretoria 0001, South Africa.
Ronald
R
Anderson
D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D001692:Biological Transport / Q000235:genetics; D027682:Cation Transport Proteins / Q000235:genetics*; D015964:Gene Expression Regulation, Bacterial / Q000235:genetics*; D006863:Hydrogen-Ion Concentration; D017136:Ion Transport / Q000235:genetics; D009169:Mycobacterium tuberculosis / Q000235:genetics*; D011188:Potassium / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics
D001426:Bacterial Proteins; D027682:Cation Transport Proteins; D012333:RNA, Messenger; D011188:Potassium