The enzyme that breaks down hydrogen peroxide in bacteria is catalase. It converts hydrogen peroxide into water and oxygen, helping protect bacterial cells from oxidative damage.
Hydrogen peroxide can form when oxygen-based metabolism or immune defenses generate reactive oxygen species. In high concentrations, it can damage proteins, membranes, and DNA. Catalase contains heme groups that help rapidly split hydrogen peroxide, often producing visible bubbles of oxygen in laboratory tests.
The catalase test is a useful way to distinguish bacterial groups. Staphylococci are generally catalase-positive, while streptococci are typically catalase-negative. Superoxide dismutase is related but performs a different job: it converts superoxide radicals into hydrogen peroxide, which catalase can then remove. Peroxidases also break down hydrogen peroxide, but catalase is the classic answer for the rapid bacterial detoxification reaction.
Catalase is not unique to bacteria; plants, fungi, and animals also use it. In humans, it is especially abundant in peroxisomes, where it helps manage peroxide produced during normal cellular chemistry.