Mycobacterium smegmatis RoxY Is a Repressor of oxyS and Contributes to Resistance to Oxidative Stress and Bactericidal Ubiquitin-Derived Peptides

Abstract

ABSTRACT The mycobactericidal properties of macrophages include the generation of reactive oxygen intermediates and the delivery of bacteria to a hydrolytic lysosome enriched in bactericidal ubiquitin-derived peptides (Ub-peptides). To better understand the interactions of ubiquitin-derived peptides with mycobacteria and identify putative mycobacterial intrinsic resistance mechanisms, we screened for transposon mutants with increased susceptibility to the bactericidal Ub-peptide Ub2. We isolated 27 Mycobacterium smegmatis mutants that were hypersusceptible to Ub2. Two mutants were isolated that possessed mutations in the msmeg _ 0166 gene, which encodes a transcriptional regulator. The msmeg _ 0166 mutants were also hypersusceptible to other host antimicrobial peptides and oxidative stress. In characterizing msmeg _ 0166 , we found that it encodes a r epressor of oxy S , and therefore we have renamed the gene roxY . We demonstrate that RoxY and OxyS contribute to M. smegmatis resistance to oxidative stress. An ahpD transposon mutant was also isolated in our screen for Ub-peptide hypersusceptibility. Overexpression of oxyS in M. smegmatis reduced transcription of the ahpCD genes, which encode a peroxide detoxification system. Our data indicate that RoxY, OxyS, and AhpD play a role in the mycobacterial oxidative stress response and are important for resistance to host antimicrobial peptides.