- Describe what catalase is and why it is important for bacterial survival.
- Give the chemical reaction catalyzed by catalase.
- Explain how testing for catalase is useful for characterizing and identifying bacterial species.
- Tell the types of bacterial species that typically produce catalase and those that typically do not produce catalase.
- Successfully conduct a catalase test.
- Interpret results for a catalase test.
Catalase is an enzyme produced by some species of bacteria. This enzyme protects bacteria from hydrogen peroxide (H2O2) that can damage and kill them. Catalase will convert hydrogen peroxide into liquid water (H2O) and oxygen gas (O2). As a result, if catalase is very active due to an abundance of hydrogen peroxide, the rapid production of oxygen gas (O2) will produce bubbles.
Figure 1: The reaction catalyzed by the enzyme catalase. Two hydrogen peroxide molecules (2 H2O2) is converted into two water molecules (2 H2O) and an oxygen molecule (O2). "Catalase" is written over the reaction arrow to show that this is the enzyme that enables this chemical reaction to occur.
Bacteria that conduct aerobic metabolism (biological reactions that require O2) produce hydrogen peroxide (H2O2) as a toxic byproduct of their metabolism. Toxic hydrogen peroxide can cause intracellular damage, such as damage to DNA, lipids, and proteins. To remove H2O2 and other similar compounds, cells produce enzymes to break them down, such as catalase.
Bacteria can only make catalase if they have the gene for catalase in their DNA. When the catalase gene is expressed by the cell (DNA-->RNA-->protein), the bacteria produce catalase. Only species that have the catalase gene will make catalase and will test catalase positive. Bacterial species that do not have the catalase gene cannot make catalase and will test catalase negative. Therefore, testing for the presence or absence of catalase is a way bacterial species can be characterized and another tool for classifying and identifying bacterial species.
Figure 2: Slide catalase test results. Hydrogen peroxide was added directly to bacteria placed on a microscope slide. A catalase positive reaction is indicated by bubbling (top); a negative reaction is indicated by lack of bubbling (bottom). Image by Karen Reiner, Andrews University, Berrien Springs, MI.
A simple test to determine if bacteria produce catalase is to add hydrogen peroxide to bacteria. This may be done by adding the hydrogen peroxide to bacteria placed on a slide or adding it to bacteria growing on an agar slant. If catalase is present, the hydrogen peroxide will be broken down into water and oxygen gas, resulting in the production of bubbles (catalase positive). This test does not require any special type of medium, however it should never be performed on organisms that have been grown on blood agar (a medium that contains blood). This is because there is a catalase activity in blood that would produce a false positive result.
Most aerobic bacteria (bacteria that require O2) and facultatively anaerobic bacteria (bacteria that live and metabolize O2 or in an environment without O2) produce catalase. Obligate anaerobe bacterial species (bacteria that must live in an environment without O2 to survive) lack catalase, which is why they cannot survive in an atmosphere containing oxygen. However, some of them have modified versions of catalase to deal with any possible exposure to oxygen.
- Obtain a glass slide and a bottle of hydrogen peroxide.
- Using a sterilized inoculating loop, smear a small amount of bacteria onto the dry slide.
- Place a drop of hydrogen peroxide on top of the bacteria.
- Look for bubbles immediately:
- bubbles = catalase positive
- no bubbles = catalase negative
Results & Questions
- Complete the table above with results from the catalase test.
- What is catalase?
- Why is catalase production an advantage for bacteria to survive?
- What types of bacteria typically produce catalase?
- What types of bacteria typically do not produce catalase?
- Give the chemical reaction catalyzed by the catalase enzyme.
- When a bacterial species produces the catalase enzyme, what does it tell us about this species genes?
- When a bacterial species does not produce the catalase enzyme, what does this tell us about this species genes?
- Why can the catalase test be used to help with bacterial identification?
- Chapter Image: Catalase reaction.jpg by Nase assumed (based on copyright claims) is licensed under CC BY-SA 3.0
- MB352 General Microbiology Laboratory 2021 (Lee) by Alice_Lee@ncsu.edu is licensed under CC BY-NC-SA 4.0
- Red Mountain Microbiology by Jill Raymond Ph.D.; Graham Boorse, Ph.D.; Anne Mason M.S. is licensed under CC BY-NC 4.0