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The enduring hypoxic response of Mycobacterium tuberculosis.

Rustad TR, Harrell MI, Liao R, Sherman DR - PLoS ONE (2008)

Bottom Line: These results suggested that additional genes may be essential for entry into and maintenance of bacteriostasis.We found that the EHR is independent of the DosR-mediated initial hypoxic response, as EHR expression is virtually unaltered in the dosR mutant.Our results suggest a reassessment of the role of DosR and the initial hypoxic response in MTB physiology.

View Article: PubMed Central - PubMed

Affiliation: Seattle Biomedical Research Institute, Seattle, Washington, USA.

ABSTRACT

Background: A significant body of evidence accumulated over the last century suggests a link between hypoxic microenvironments within the infected host and the latent phase of tuberculosis. Studies to test this correlation have identified the M. tuberculosis initial hypoxic response, controlled by the two-component response regulator DosR. The initial hypoxic response is completely blocked in a dosR deletion mutant.

Methodology/principal findings: We show here that a dosR deletion mutant enters bacteriostasis in response to in vitro hypoxia with only a relatively mild decrease in viability. In the murine infection model, the phenotype of the mutant was indistinguishable from that of the parent strain. These results suggested that additional genes may be essential for entry into and maintenance of bacteriostasis. Detailed microarray analysis of oxygen starved cultures revealed that DosR regulon induction is transient, with induction of nearly half the genes returning to baseline within 24 hours. In addition, a larger, sustained wave of gene expression follows the DosR-mediated initial hypoxic response. This Enduring Hypoxic Response (EHR) consists of 230 genes significantly induced at four and seven days of hypoxia but not at initial time points. These genes include a surprising number of transcriptional regulators that could control the program of bacteriostasis. We found that the EHR is independent of the DosR-mediated initial hypoxic response, as EHR expression is virtually unaltered in the dosR mutant.

Conclusions/significance: Our results suggest a reassessment of the role of DosR and the initial hypoxic response in MTB physiology. Instead of a primary role in survival of hypoxia induced bacteriostasis, DosR may regulate a response that is largely optional in vitro and in mouse infections. Analysis of the EHR should help elucidate the key regulatory factors and enzymatic machinery exploited by M. tuberculosis for long-term bacteriostasis in the face of oxygen deprivation.

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Related in: MedlinePlus

Downstream hypoxic response independent of DosR regulon.Each bar represents the number of genes induced in H37Rv at each point during a short hypoxic time course (>two fold in all three arrays). The DosR regulon represents a dwindling fraction of the genes induced over time (gray). Very few genes were induced in H37Rv and not in the dosR mutant (diagonal lines). The overwhelming majority of genes induced in the parent strain at later hypoxic time points were also induced in the mutant (black).
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pone-0001502-g004: Downstream hypoxic response independent of DosR regulon.Each bar represents the number of genes induced in H37Rv at each point during a short hypoxic time course (>two fold in all three arrays). The DosR regulon represents a dwindling fraction of the genes induced over time (gray). Very few genes were induced in H37Rv and not in the dosR mutant (diagonal lines). The overwhelming majority of genes induced in the parent strain at later hypoxic time points were also induced in the mutant (black).

Mentions: We sought to define the link between the initial hypoxic response controlled by DosR and the EHR. Accordingly, three paired H37Rv and H37Rv:ΔdosR hypoxic time courses were conducted. Samples were taken at four, eight, twelve, and 24 hours of exposure to hypoxia. As before, microarrays were used to compare RNA from each strain at each hypoxic time point to log phase expression. To avoid threshold effects caused when modestly induced genes wobble across the two-fold threshold, we applied a more stringent criterion (>2 fold in all three arrays) to define the set of genes induced at each time-point. The genes induced at each time-point were divided into three classes: (1) induced in both H37Rv and the dosR mutant, (2) the DosR regulon genes, which are not induced in the dosR mutant, and (3) the genes outside the DosR regulon that are induced in H37Rv but not the mutant (Figure 4). If EHR expression depends significantly on the DosR response, we would expect a large number of genes in that final category.


The enduring hypoxic response of Mycobacterium tuberculosis.

Rustad TR, Harrell MI, Liao R, Sherman DR - PLoS ONE (2008)

Downstream hypoxic response independent of DosR regulon.Each bar represents the number of genes induced in H37Rv at each point during a short hypoxic time course (>two fold in all three arrays). The DosR regulon represents a dwindling fraction of the genes induced over time (gray). Very few genes were induced in H37Rv and not in the dosR mutant (diagonal lines). The overwhelming majority of genes induced in the parent strain at later hypoxic time points were also induced in the mutant (black).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2198943&req=5

pone-0001502-g004: Downstream hypoxic response independent of DosR regulon.Each bar represents the number of genes induced in H37Rv at each point during a short hypoxic time course (>two fold in all three arrays). The DosR regulon represents a dwindling fraction of the genes induced over time (gray). Very few genes were induced in H37Rv and not in the dosR mutant (diagonal lines). The overwhelming majority of genes induced in the parent strain at later hypoxic time points were also induced in the mutant (black).
Mentions: We sought to define the link between the initial hypoxic response controlled by DosR and the EHR. Accordingly, three paired H37Rv and H37Rv:ΔdosR hypoxic time courses were conducted. Samples were taken at four, eight, twelve, and 24 hours of exposure to hypoxia. As before, microarrays were used to compare RNA from each strain at each hypoxic time point to log phase expression. To avoid threshold effects caused when modestly induced genes wobble across the two-fold threshold, we applied a more stringent criterion (>2 fold in all three arrays) to define the set of genes induced at each time-point. The genes induced at each time-point were divided into three classes: (1) induced in both H37Rv and the dosR mutant, (2) the DosR regulon genes, which are not induced in the dosR mutant, and (3) the genes outside the DosR regulon that are induced in H37Rv but not the mutant (Figure 4). If EHR expression depends significantly on the DosR response, we would expect a large number of genes in that final category.

Bottom Line: These results suggested that additional genes may be essential for entry into and maintenance of bacteriostasis.We found that the EHR is independent of the DosR-mediated initial hypoxic response, as EHR expression is virtually unaltered in the dosR mutant.Our results suggest a reassessment of the role of DosR and the initial hypoxic response in MTB physiology.

View Article: PubMed Central - PubMed

Affiliation: Seattle Biomedical Research Institute, Seattle, Washington, USA.

ABSTRACT

Background: A significant body of evidence accumulated over the last century suggests a link between hypoxic microenvironments within the infected host and the latent phase of tuberculosis. Studies to test this correlation have identified the M. tuberculosis initial hypoxic response, controlled by the two-component response regulator DosR. The initial hypoxic response is completely blocked in a dosR deletion mutant.

Methodology/principal findings: We show here that a dosR deletion mutant enters bacteriostasis in response to in vitro hypoxia with only a relatively mild decrease in viability. In the murine infection model, the phenotype of the mutant was indistinguishable from that of the parent strain. These results suggested that additional genes may be essential for entry into and maintenance of bacteriostasis. Detailed microarray analysis of oxygen starved cultures revealed that DosR regulon induction is transient, with induction of nearly half the genes returning to baseline within 24 hours. In addition, a larger, sustained wave of gene expression follows the DosR-mediated initial hypoxic response. This Enduring Hypoxic Response (EHR) consists of 230 genes significantly induced at four and seven days of hypoxia but not at initial time points. These genes include a surprising number of transcriptional regulators that could control the program of bacteriostasis. We found that the EHR is independent of the DosR-mediated initial hypoxic response, as EHR expression is virtually unaltered in the dosR mutant.

Conclusions/significance: Our results suggest a reassessment of the role of DosR and the initial hypoxic response in MTB physiology. Instead of a primary role in survival of hypoxia induced bacteriostasis, DosR may regulate a response that is largely optional in vitro and in mouse infections. Analysis of the EHR should help elucidate the key regulatory factors and enzymatic machinery exploited by M. tuberculosis for long-term bacteriostasis in the face of oxygen deprivation.

Show MeSH
Related in: MedlinePlus