NemR Is a Bleach-sensing Transcription Factor

Abstract

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.

Mechanisms of Increased Resistance to Chlorhexidine and Cross-Resistance to Colistin following Exposure of Klebsiella pneumoniae Clinical Isolates to Chlorhexidine

“…Divergent expression from the same promoter is commonly observed in genes that are negatively regulated by Tet repressors (16). Examples of TetR homologues involved in resistance to biocides are QacR in Staphylococcus aureus and EnvR and NemR in Escherichia coli (17)(18)(19).…”

Does the Transcription Factor NemR Use a Regulatory Sulfenamide Bond to Sense Bleach?

“…We previously demonstrated that MGO accumulates in RCS-stressed E. coli as part of a pathway facilitating production of polyphosphate, a biopolymer that prevents the aggregation of oxidized proteins (4). It is therefore not surprising that both NemA and GloA are necessary for HOCl survival in E. coli (3).…”

“…To survive RCS exposure, Escherichia coli mounts a complex and still incompletely understood stress response that is coordinated by several different transcriptional regulators (2). These are distinct from the transcription factors that sense reactive oxygen species (ROS) and include the repressor NemR (2,3).…”

“…NemR integrates the E. coli stress responses to both RCS and toxic electrophiles (3,6,8). NemR controls expression of three proteins: itself, NemA, and GloA.…”

Tetramers Are the Activation-competent Species of the HOCl-specific Transcription Factor HypT

“…These include the chaperone Hsp33, which in its active state prevents irreversible aggregation of proteins, and the regulators NemR, HypR, and HypT, which in turn regulate genes that support survival of the stress (6 -10). Whereas Hsp33, NemR, and HypR are activated by oxidation of cysteine thiols (7,8,11), HypT is activated by HOCl by simultaneous oxidation of three methionines (Met-123, Met-206, and Met-230) to methionine sulfoxide, thus forming the active HypT species (10). This active state can be mimicked by methionine-to-glutamine substitution, leading to the constitutively active mutant HypT M123,206,230Q (10).…”