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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 absolute expression of the trk and kdp genes in the WT and trk-gene knockout cells at mid-log phase suspended in growth medium of varying pH. (a), (b), (c), and (d) represent the absolute expression (μg/mL) of the ceoB, kdpA, kdpD, and sigA genes, respectively. Normal represents bacteria cultured in 7H9 broth without adjustment of the pH. The results are of three experiments in duplicate for each gene. Statistical significance was determined in relation to the absolute quantity of each gene at pH 7. ∗p < 0.05.
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fig2: The absolute expression of the trk and kdp genes in the WT and trk-gene knockout cells at mid-log phase suspended in growth medium of varying pH. (a), (b), (c), and (d) represent the absolute expression (μg/mL) of the ceoB, kdpA, kdpD, and sigA genes, respectively. Normal represents bacteria cultured in 7H9 broth without adjustment of the pH. The results are of three experiments in duplicate for each gene. Statistical significance was determined in relation to the absolute quantity of each gene at pH 7. ∗p < 0.05.

Mentions: For these experiments, based on simultaneous expression of genes from the same operons (Table 3), gene expression was evaluated on one gene of each operon [7] with sigA included as a reference gene. All genes, including the sigA, were significantly upregulated at pH 5.5 and highest in the trk-gene knockout strain. The magnitudes of expression of the ceoB and kdpA genes were pH-dependent being inversely related to decreasing extracellular pH. Relative to the mutant strain, however, induction of the kdpA and kdpD genes was less significant in the WT strain (Figure 2). These results indicate that both K+-uptake systems are induced at pH 5.5. However, as the pH increases from 6 to 6.5 the expression of the trk genes decreases significantly, while the kdp genes remain suppressed in the presence of functional Trk system.


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 absolute expression of the trk and kdp genes in the WT and trk-gene knockout cells at mid-log phase suspended in growth medium of varying pH. (a), (b), (c), and (d) represent the absolute expression (μg/mL) of the ceoB, kdpA, kdpD, and sigA genes, respectively. Normal represents bacteria cultured in 7H9 broth without adjustment of the pH. The results are of three experiments in duplicate for each gene. Statistical significance was determined in relation to the absolute quantity of each gene at pH 7. ∗p < 0.05.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig2: The absolute expression of the trk and kdp genes in the WT and trk-gene knockout cells at mid-log phase suspended in growth medium of varying pH. (a), (b), (c), and (d) represent the absolute expression (μg/mL) of the ceoB, kdpA, kdpD, and sigA genes, respectively. Normal represents bacteria cultured in 7H9 broth without adjustment of the pH. The results are of three experiments in duplicate for each gene. Statistical significance was determined in relation to the absolute quantity of each gene at pH 7. ∗p < 0.05.
Mentions: For these experiments, based on simultaneous expression of genes from the same operons (Table 3), gene expression was evaluated on one gene of each operon [7] with sigA included as a reference gene. All genes, including the sigA, were significantly upregulated at pH 5.5 and highest in the trk-gene knockout strain. The magnitudes of expression of the ceoB and kdpA genes were pH-dependent being inversely related to decreasing extracellular pH. Relative to the mutant strain, however, induction of the kdpA and kdpD genes was less significant in the WT strain (Figure 2). These results indicate that both K+-uptake systems are induced at pH 5.5. However, as the pH increases from 6 to 6.5 the expression of the trk genes decreases significantly, while the kdp genes remain suppressed in the presence of functional Trk system.

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