Clean results: U-M researchers learn how bleach kills bacteria
Developed more than 200 years ago and found in households around the world, chlorine bleach is among the most widely used disinfectants, yet scientists never have understood exactly how the familiar product kills bacteria.
New research, however, reveals key details in the process by which bleach works its antimicrobial magic.
In a study published in the Nov. 14 issue of the journal Cell, a team led by molecular biologist Ursula Jakob describes a mechanism by which hypochlorite, the active ingredient of household bleach, attacks essential bacterial proteins, ultimately killing the bugs.
"As so often happens in science, we did not set out to address this question," says Jakob, an associate professor of molecular, cellular and developmental biology at LSA. "But when we stumbled on the answer midway through a different project, we were all very excited."
Jakob and her team members were studying a bacterial protein known as heat shock protein 33 (Hsp33), which is classified as a molecular chaperone. The main job of chaperones is to protect proteins from unfavorable interactions, a function that's particularly important when cells are under conditions of stress, such as the high temperatures that result from fever.
"At high temperatures, proteins begin to lose their three-dimensional molecular structure and start to clump together and form large, insoluble aggregates, just like when you boil an egg," says lead author Jeannette Winter, who was a postdoctoral fellow in Jakob's lab. And like eggs, which once boiled never turn liquid again, aggregated proteins usually remain insoluble, and the stressed cells eventually die.
Jakob and her research team figured out that bleach and high temperatures have very similar effects on proteins. Just like heat, the hypochlorite in bleach causes proteins to lose their structure and form large aggregates.
"Many of the proteins that hypochlorite attacks are essential for bacterial growth, so inactivating those proteins likely kills the bacteria," says second author Marianne Ilbert, a postdoctoral fellow in Jakob's lab.
These findings not only are important for understanding how bleach keeps kitchen countertops sanitary, but they may lead to insights into how humans fight off bacterial infections. Immune cells produce significant amounts of hypochlorite as a first line of defense to kill invading microorganisms. Unfortunately, hypochlorite damages not just bacterial cells, but human cells as well. It is the uncontrolled production of hypochlorite acid that is thought to cause tissue damage at sites of chronic inflammation.
How did studying the protein Hsp33 lead to the bleach discovery? The researchers learned that hypochlorite, rather than damaging Hsp33 as it does most proteins, actually revs up the molecular chaperone. When bacteria encounter the disinfectant, Hsp33 jumps into action to protect bacterial proteins against bleach-induced aggregation.
"With Hsp33, bacteria have evolved a very clever system that directly senses the insult, responds to it and increases the bacteria's resistance to bleach," Jakob says.