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

Cholo MC, van Rensburg EJ, Osman AG, Anderson R - Biomed Res Int (2015)

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Immunology, Faculty of Health Sciences, University of Pretoria, Pretoria 0001, South Africa.

ABSTRACT
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.

No MeSH data available.


Related in: MedlinePlus

The membrane potential values of  WT and trk-gene knockout strains at varying extracellular pH levels. The results represent nine replicates from three experiments represented as absolute fluorescence ± SEM. Statistical significance was determined in relation to membrane potential observed at pH 7 for each strain and between the strains at each pH level. ∗p < 0.05.
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fig5: The membrane potential values of  WT and trk-gene knockout strains at varying extracellular pH levels. The results represent nine replicates from three experiments represented as absolute fluorescence ± SEM. Statistical significance was determined in relation to membrane potential observed at pH 7 for each strain and between the strains at each pH level. ∗p < 0.05.

Mentions: In the case of both strains upregulation of gene expression coincided with decreases in the rate of growth, uptake of 86Rb+, membrane potentials, and extracellular pH which dropped to 5.5 (Figures 3, 4, and 5).


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

Cholo MC, van Rensburg EJ, Osman AG, Anderson R - Biomed Res Int (2015)

The membrane potential values of  WT and trk-gene knockout strains at varying extracellular pH levels. The results represent nine replicates from three experiments represented as absolute fluorescence ± SEM. Statistical significance was determined in relation to membrane potential observed at pH 7 for each strain and between the strains at each pH level. ∗p < 0.05.
© Copyright Policy - open-access
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4553272&req=5

fig5: The membrane potential values of  WT and trk-gene knockout strains at varying extracellular pH levels. The results represent nine replicates from three experiments represented as absolute fluorescence ± SEM. Statistical significance was determined in relation to membrane potential observed at pH 7 for each strain and between the strains at each pH level. ∗p < 0.05.
Mentions: In the case of both strains upregulation of gene expression coincided with decreases in the rate of growth, uptake of 86Rb+, membrane potentials, and extracellular pH which dropped to 5.5 (Figures 3, 4, and 5).

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Immunology, Faculty of Health Sciences, University of Pretoria, Pretoria 0001, South Africa.

ABSTRACT
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.

No MeSH data available.


Related in: MedlinePlus