In my AS level chemistry class, students study the disproportionation reaction of chlorine with alkali. In this reaction chlorine gets oxidized and reduced. While studying this topic one of the students asked how chlorine actually kills microbes. This news article published by the British journal Nature in 2008 responds to his question:

…Now, researchers have found that bleach can kill bacteria by attacking proteins, quickly destroying their delicate shape. Furthermore, the model bacterium Escherichia colieven produces a protein that is activated by bleach and rescues injured proteins before the damage becomes permanent…

To the researcher’s surprise, they found a protein which was unperturbed by the killer chlorine

…In fact, Hsp33 (heat shock protein) becomes more active when cells are exposed to hypochlorous acid. When bleach reacts with some of this protein’s amino acids, Hsp33 partly unfolds and assumes an active structure. This is unusual: unfolding renders most proteins non-functional, yet for Hsp33 the process acts as switch to turn the protein on…

Read more… Source: Nature…

Specifically, hypochlorite can activate Hsp33 within 1 minute at both high and low temperatures. However, in mutants of Escherichia coli lacking the Hsp33 gene, exposure to hypochlorite leads proteins to aggregate 1.5- to 17-times more than in wild-type cells containing Hsp33. Activated Hsp33 appears to protect proteins against bleach-induced aggregation, and it may increase the resistance of wild-type E. coli to bleach. Vibrio cholera mutants missing the Hsp33 gene behave similarly, suggesting that the protective function of Hsp33 may be conserved across species. Read more in American Society of Microbiology

Original research article: Cell

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