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Review
. 2013;67:141-60.
doi: 10.1146/annurev-micro-102912-142520. Epub 2013 Jun 14.

Bacterial Responses to Reactive Chlorine Species

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Free PMC article
Review

Bacterial Responses to Reactive Chlorine Species

Michael J Gray et al. Annu Rev Microbiol. .
Free PMC article

Abstract

Hypochlorous acid (HOCl), the active ingredient of household bleach, is the most common disinfectant in medical, industrial, and domestic use and plays an important role in microbial killing in the innate immune system. Given the critical importance of the antimicrobial properties of chlorine to public health, it is surprising how little is known about the ways in which bacteria sense and respond to reactive chlorine species (RCS). Although the literature on bacterial responses to reactive oxygen species (ROS) is enormous, work addressing bacterial responses to RCS has begun only recently. Transcriptomic and proteomic studies now provide new insights into how bacteria mount defenses against this important class of antimicrobial compounds. In this review, we summarize the current knowledge, emphasizing the overlaps between RCS stress responses and other more well-characterized bacterial defense systems, and identify outstanding questions that represent productive avenues for future research.

Figures

Figure 1
Figure 1
Reactions of hypochlorous acid (HOCl) with biomolecules. Reaction of HOCl with (a) sulfur-containing compounds or (b) amines. Brackets indicate unstable reactive intermediates. Enzymes known to repair oxidized cysteine or methionine residues in bacteria are indicated. Asterisks indicate irreversibly oxidized dead-end products.
Figure 2
Figure 2
Bacterial responses to protein damage by reactive chlorine species (RCS). Hypochlorous acid (HOCl) reacts rapidly with proteins, leading to side chain oxidation and unfolding. Low-molecular-weight thiols (e.g., GSH) react with RCS and reduce their effective concentration. Repair enzymes, including methionine sulfoxide reductase (Msr), thioredoxin (Trx), and Fe-S cluster repair systems (Nif/Suf/Isc), can reverse oxidative protein damage. Metal ions released from damaged proteins promote radical formation. Dps and YggX sequester metals and minimize metal-catalyzed oxidative damage. Chaperones, particularly Hsp33, prevent aggregation of unfolded proteins, and proteases degrade irreversibly damaged proteins.

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