Affiliation:
1. Center of Excellence in Infectious Diseases, Department of Biomedical Sciences, Paul L. Foster School of Medicine, Texas Tech University Health Sciences Center, El Paso, Texas, USA
Abstract
ABSTRACT
The organic hydroperoxide stress resistance regulator (OhrR) is a MarR type of transcriptional regulator that primarily regulates the expression of organic hydroperoxide reductase (Ohr) in bacteria. In mycobacteria, the genes encoding these proteins exist in only a few species, which include the fast-growing organism
Mycobacterium smegmatis
. To delineate the roles of Ohr and OhrR in defense against oxidative stress in
M. smegmatis
, strains lacking the expression of these proteins were constructed by deleting the
ohrR
and
ohr
genes, independently and together, through homologous recombination. The OhrR mutant strain (MSΔohrR) showed severalfold upregulation of Ohr expression, which could be observed at both the transcript and protein levels. Similar upregulation of Ohr expression was also noticed in an
M. smegmatis
wild-type strain (MSWt) induced with cumene hydroperoxide (CHP) and
t
-butyl hydroperoxide (
t
-BHP). The elevated Ohr expression in MSΔohrR correlated with heightened resistance to oxidative stress due to CHP and
t
-BHP and to inhibitory effects due to the antituberculosis drug isoniazid (INH). Further, this mutant strain exhibited significantly enhanced survival in the intracellular compartments of macrophages. In contrast, the strains lacking either Ohr alone (MSΔohr) or both Ohr and OhrR (MSΔohr-ohrR) displayed limited or no resistance to hydroperoxides and INH. Additionally, these strains showed no significant differences in intracellular survival from the wild type. Electrophoretic mobility shift assays (EMSAs) revealed that the overexpressed and purified OhrR interacts with the
ohr-ohrR
intergenic region with a greater affinity and this interaction is contingent upon the redox state of the OhrR. These findings suggest that Ohr-OhrR is an important peroxide stress response system in
M. smegmatis
.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
26 articles.
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