Abstract
Little is known about how bacteria sense or respond to reactive chlorine species, such as bleach. NemR is a redox-regulated transcription factor which senses bleach. NemR controls expression of genes encoding electrophile detoxification enzymes, which increase bleach resistance. We demonstrate a bleach-sensing bacterial response system and a new mechanism contributing to bacterial bleach survival. Hypochlorous acid (HOCl), the active component of household bleach, also functions as a powerful antimicrobial during the innate immune response. Despite its widespread use, surprisingly little is known about how cells sense or respond to HOCl. We now demonstrate that Escherichia coli NemR is a redox-regulated transcriptional repressor, which uses the oxidation status of HOCl-sensitive cysteine residues to respond to bleach and related reactive chlorine species. NemR controls bleach-mediated expression of two enzymes required for detoxification of reactive electrophiles: glyoxalase I and N-ethylmaleimide reductase. Both enzymes contribute to bacterial bleach survival. These results provide evidence that bleach resistance relies on the capacity of organisms to specifically sense reactive chlorine species and respond with the up-regulation of enzymes dedicated to detoxification of methylglyoxal and other reactive electrophiles.
Highlights
Little is known about how bacteria sense or respond to reactive chlorine species, such as bleach
Identification of Bleach-responsive Regulators in E. coli—To identify regulators that might contribute to bacterial bleach defense, we examined gene expression in E. coli before and after a sublethal dose of Hypochlorous acid (HOCl) (0.4 mM) using a transcriptional microarray, the full results of which are shown in supplemental Table S1
Pretreatment of E. coli with 0.4 mM HOCl protected against methylglyoxal stress (Fig. 2C), as would be expected due to NemR-dependent up-regulation of gloA. ⌬nemA mutants showed no defect in survival of methylglyoxal stress, indicating that NemA is more important for HOCl stress tolerance than for resistance to exogenous methylglyoxal (Fig. 2, A and B). Consistent with these results, HPLC analysis of HOCl-treated E. coli revealed substantial accumulation of intracellular methylglyoxal after HOCl treatment (Fig. 2D). These results suggest that NemR is a bacterial repressor which is sensitive to HOCl and related reactive chlorine species (RCS) and whose gene products contribute to increased bleach resistance in E. coli by detoxifying reactive electrophiles produced during RCS stress
Summary
Little is known about how bacteria sense or respond to reactive chlorine species, such as bleach. Surprisingly little is known about how cells sense or respond to HOCl. We demonstrate that Escherichia coli NemR is a redox-regulated transcriptional repressor, which uses the oxidation status of HOCl-sensitive cysteine residues to respond to bleach and related reactive chlorine species. It is naturally generated during the microbicidal oxidative burst of neutrophils and appears to play a key role in controlling bacterial colonization of mucosal epithelia (2, 3) Despite this physiological importance, little is known about how bacteria sense or defend themselves against reactive chlorine species (RCS), which include HOCl, chloramines, and other related compounds that are able to chlorinate and oxidize biomolecules (4). We demonstrate that bleach-mediated up-regulation of the NemR-controlled genes gloA and nemA increases bacterial bleach survival, providing the first evidence that resistance toward bleach relies on the ability of bacteria to detoxify methylglyoxal and reactive electrophiles
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