title: Inactivation of the organic hydroperoxide stress resistance regulator OhrR enhances resistance to oxidative stress and isoniazid in Mycobacterium smegmatis.
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.
authors.affiliation: 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.
authors.forename: Sankaralingam
authors.initials: S
authors.lastname: Saikolappan
authors.affiliation: 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.
authors.forename: Kishore
authors.initials: K
authors.lastname: Das
authors.affiliation: 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 s.dhandayuthapani@ttuhsc.edu.
authors.forename: Subramanian
authors.initials: S
authors.lastname: Dhandayuthapani
mesh_terms: D000995:Antitubercular Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D024881:Drug Resistance, Bacterial; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects / Q000502:physiology; D020868:Gene Silencing; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D007538:Isoniazid / Q000494:pharmacology*; D008264:Macrophages; D008826:Microbial Sensitivity Tests; D020102:Mycobacterium smegmatis / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D018384:Oxidative Stress / Q000502:physiology*; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D000995:Antitubercular Agents; D001426:Bacterial Proteins; D012097:Repressor Proteins; C122138:peroxide repressor proteins; D006861:Hydrogen Peroxide; D007538:Isoniazid