How can facultative anaerobes exist without catalase?

How can facultative anaerobes exist without catalase?

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Catalase-negative bacteria may be anaerobes, or they may be facultative anaerobes that only ferment and do not respire using oxygen as a terminal electron acceptor

A facultative anaerobe is an organism that makes ATP by aerobic respiration if oxygen is present, but is capable of switching to fermentation or anaerobic respiration if oxygen is absent

But if facultative anaerobes can be present in oxygen rich environments, don't they have to have catalase in order not to die?

There is another class of peroxide decomposing enzymes called peroxidases. These enzymes can catalyze the reduction of $ce{H2O2}$ to water using an electron donor. However, unlike in the catalase reaction, the electron donor is not another $ce{H2O2}$ molecule and no molecular oxygen is produced. Thus their presence would not be detected by the typical spot catalase test (which looks for gaseous oxygen generation). For example, NADH peroxidase catalyzes the following reaction to protect cells from oxidative damage:

$$ce{NADH + H+ + H2O2 -> NAD+ + 2H2O}$$

Thus catalase negative organisms can still have a means of protection against $ce{H2O2}$. You can read more in this textbook, specifically the section titled "Oxygen Toxicity".


Q-Could you please tell me if the term ''anaerobe'' describes a dangerous condition or disease? This information is most important to me.

A-You must have overheard conversations at your doctor`s office. Anaerobes are a type of bacteria. All bacteria are divided roughly into two types: those that must have oxygen to develop, or aerobic bacteria, and those that can live and grow without it, anaerobic bacteria, or simply anaerobes.

As with other microbes, not all anaerobes are dangerous. In fact, anaerobes are commonly found on our skin and mucus membranes, where they do no harm until damage or disease lets them into deeper tissue. There, little oxygen is present and anaerobes are in a situation that favors their growth, and an infection occurs. Some infections, called mixed infections, are caused by combinations of anaerobic and aerobic bacteria.

The classic anaerobic infection is gangrene, where tissue that has had its blood supply (and thus oxygen supply) cut off becomes anaerobically infected, and dies. Abscesses, pockets of infection that are closed off, are commonly caused by anaerobes, as is peritonitis. The hallmark of an anaerobic infection is a foul or putrid odor.

Anaerobic infections can occur after surgery, especially abdominal operations, but surgery is also one of the best ways to treat an anaerobic infection. Simply opening up and cleaning out an abscess will let in oxygen that stops the anaerobic growth. In some cases, a surgeon will put in a drainage tube to drain the infection site. Anaerobes are hard to kill with antibiotics, but some strains of anaerobic bacteria do respond to drug therapy.


Bacteria, including those that are pathogenic, have been generally classified according to their ability to survive and grow in the presence or absence of oxygen: aerobic and anaerobic bacteria, respectively. Strict aerobes require oxygen to grow (e.g., Neisseria), and strict anaerobes grow exclusively without, and do not survive oxygen exposure (e.g., Clostridia) aerotolerant bacteria (e.g., Lactobacilli) are insensitive to oxygen exposure. Facultative anaerobes (e.g., E. coli) have the unique ability to grow in the presence or in the absence of oxygen and are thus well-adapted to these changing conditions, which may constitute an underestimated selective advantage for infection. In the WHO antibiotic-resistant ‘priority pathogens’ list, facultative anaerobes are overrepresented (8 among 12 listed pathogens), consistent with clinical studies performed in populations particularly susceptible to infectious diseases. Bacteria aerobic respiratory chain plays a central role in oxygen consumption, leading to the formation of hypoxic infectious sites (infectious hypoxia). Facultative anaerobes have developed a wide diversity of aerotolerance and anaerotolerance strategies in vivo. However, at a single cell level, the modulation of the intracellular oxygen level in host infected cells remains elusive and will be discussed in this review. In conclusion, the ability of facultative bacteria to evolve in the presence or the absence of oxygen is essential for their virulence strategy and constitute a selective advantage.

Take Away

  • Most life-threatening pathogenic bacteria are facultative anaerobes.
  • Only facultative anaerobes are aerotolerant, anaerotolerant and capable of consuming O2.
  • Facultative anaerobes induce and are well adapted to cellular hypoxia.

Bacterial Vaginosis

Jeanne M. Marrazzo , Sharon L. Hillier , in Sexually Transmitted Diseases (Second Edition) , 2013

Pelvic Inflammatory Disease

Anaerobes have long been linked with salpingitis ( Sweet, 2000 ). Many of the bacteria recovered from the endometrium and Fallopian tubes of patients with PID are those present in the vagina in high numbers among women with BV ( Soper et al., 1994 ). However, likely interactions between Chlamydia trachomatis, N. gonorrhoeae, and facultative bacteria in producing PID have not been well defined, and the relationship between BV or intermediate flora and acquisition of C. trachomatis and N. gonorrhoeae is probably complex and may depend in part on the microbiologic composition of BV itself. In one study that prospectively followed more than 1000 women for 3 years, BV at baseline was associated with concurrent chlamydial or gonococcal infection (adjusted OR 2.8, 95% CI 1.81–4.42) but not significantly with subsequent detection of either of these pathogens at follow-up visits (RR 1.52, 95% CI 0.74–3.13). However, among women whose BV at baseline was characterized by dense growth of pigmented, anaerobic Gram-negative rods, risk of subsequent detection of chlamydia or gonorrhea was increased (RR 1.93, 95% CI 0.97–3.83)( Ness et al., 2005 ).

In a study of symptomatic women presenting for care, endometrial biopsies were obtained on 178 consecutive women with suspected PID ( Hillier et al., 1996 ). Endometrial specimens and cervical swabs were tested for N. gonorrhoeae and C. trachomatis. Eighty-five of the patients also underwent laparoscopy to confirm a clinical diagnosis of salpingitis. Among women with endometritis, 27% had N.gonorrhoeae present in the endometrium, while 13% had endometrial C. trachomatis. Approximately 50% of the patients with endometritis had anaerobic Gram-negative rods in their endometrial samples. Endometrial N. gonorrhoeae was independently associated with a fivefold increase in endometritis, which was similar for endometrial C. trachomatis (OR 4.8) and anaerobic Gram-negative rods (OR 2.6), respectively. BV was not an independent risk factor for endometritis in the absence of endometrial anaerobes. More recently, Wiesenfeld performed endometrial biopsies on women with BV (and other lower genital tract infections, including chlamydia and gonorrhea) but without symptoms or signs of acute PID ( Wiesenfeld et al., 2002 ). Among 377 women with BV, 58 (15%) had evidence of subclinical PID (defined as the presence of 5 neutrophils per 400× field and 1 plasma cell per 120× field of endometrial tissue), while plasma cell endometritis (defined as the presence of at least 1 plasma cell per 120 of endometrial tissue) was present in 90 (24%). Subclinical PID, but not plasma cell endometritis, was more common in women with BV than in women without BV. Women with intermediate vaginal flora on Gram stain were at intermediate risk for subclinical PID (P < 0.05, test for trend), but not plasma cell endometritis. In a multivariate model that included proliferative phase of the menstrual cycle, previous pregnancy, black race, and current infection with N. gonorrhoeae, C. trachomatis, BV, or T. vaginalis, subclinical PID remained significantly associated with BV (adjusted OR 2.7, 95% CI 1.02–7.2).


One of the former definitions of “obligate anaerobiosis” was based on three main criteria: 1) it occurs in organisms, so-called obligate anaerobes, which live in environments without oxygen (O2), 2) O2-dependent (aerobic) respiration, and 3) antioxidant enzymes are absent in obligate anaerobes. In contrast, aerobes need O2 in order to grow and develop properly. Obligate (or strict) anaerobes belong to prokaryotic microorganisms from two domains, Bacteria and Archaea. A closer look at anaerobiosis covers a wide range of microorganisms that permanently or in a time-dependent manner tolerate different concentrations of O2 in their habitats. On this basis they can be classified as obligate/facultative anaerobes, microaerophiles and nanaerobes. Paradoxically, O2 tolerance in strict anaerobes is usually, as in aerobes, associated with the activity of the antioxidant response system, which involves different antioxidant enzymes responsible for removing excess reactive oxygen species (ROS). In our opinion, the traditional definition of “obligate anaerobiosis” loses its original sense. Strict anaerobiosis should only be restricted to the occurrence of O2-independent pathways involved in energy generation. For that reason, a term better than “obligate anaerobes” would be O2/ROS tolerant anaerobes, where the role of the O2/ROS detoxification system is separated from O2-independent metabolic pathways that supply energy. Ubiquitous key antioxidant enzymes like superoxide dismutase (SOD) and superoxide reductase (SOR) in contemporary obligate anaerobes might suggest that their origin is ancient, maybe even the beginning of the evolution of life on Earth. It cannot be ruled out that c. 3.5 Gyr ago, local microquantities of O2/ROS played a role in the evolution of the last universal common ancestor (LUCA) of all modern organisms. On the basis of data in the literature, the hypothesis that LUCA could be an O2/ROS tolerant anaerobe is discussed together with the question of the abiotic sources of O2/ROS and/or the early evolution of cyanobacteria that perform oxygenic photosynthesis.

Two Types of Anaerobes

There are two main types of anaerobes: facultative and obligate. Facultative anaerobes can live with or without oxygen. When oxygen is present in their environment, they use aerobic cellular respiration to produce energy in the form of ATP. If oxygen becomes depleted, they can switch to anaerobic respiration or fermentation. In contrast, obligate anaerobes must live without oxygen. They are only equipped to undergo anaerobic respiration or fermentation, and the presence of oxygen kills them.

Facultative Anaerobes

Human muscle cells are facultative anaerobes. During exercise in which a person gets plenty of oxygen to their muscles, like distance running, the cells undergo aerobic respiration. But during intense exercise such as sprinting, in which the body’s oxygen needs outstrip the lungs’ ability to provide it, muscle cells will switch to lactic acid fermentation. This process is much less efficient than aerobic respiration and produces lactic acid as a byproduct, which builds up in the muscles and causes the burning sensation commonly felt during strenuous exercise. Because this is so much less efficient, a person can only do such intense activity for a very short period of time before “hitting the wall” and having to stop.

Another familiar facultative anaerobe is the bacterium Escherichia coli. While E.coli has had a bad rap in the press due to incidents of food poisoning, E.coli are actually very important and beneficial residents of the human gastrointestinal tract. They aid in digestion of food and absorption of necessary vitamins, as well as protection from potentially harmful infections. These bacteria can easily function with or without oxygen, which makes them highly adaptable to different environments. In the anaerobic intestine, they use fermentation to produce energy. If found in the oxygen-rich environment outside the gut, they switch to aerobic respiration.

Other Examples of Facultative Anaerobes

  • Staphylococcus aureus: Causes staph infections. Methicillin-resistant S. aureus is responsible for MRSA.
  • Lactococcus lactis: Its lactic acid fermentation is used in processing many types of cheese.

Obligate Anaerobes

One infamous example of an obligate anaerobe is Clostridium botulinum. This common bacterium produces a potent neurotoxin that can be fatal in even small amounts. It is found growing in items such as home-canned products, baked potatoes wrapped in aluminum foil, and honey. Under poor survival conditions, C. botulinum produces spores with a tough coat that allows them to survive for years. When conditions improve, the bacteria begin to grow and produce potentially lethal toxins. If a person consumes food contaminated with actively growing C. botulinum they are likely to succumb to a deadly food poisoning called botulism, the early symptoms of which are nausea, vomiting, and weakness. Then come the neurological effects: blurred vision, difficulty speaking and swallowing, and impaired muscle control, followed by difficulty in breathing and possibly death by asphyxia. Infantile botulism occurs after a baby ingests C. botulinum spores, which may be found in soil, dust, or honey. This is why young babies should never be given honey before one year of age, their immune system isn’t strong enough to handle the spores, so they begin to grow and cause severe illness.

Other Examples of Obligate Anaerobes

  • Clostridium tetani: Causes tetanus
  • Chlorobium, Chloroflexus and several other species contribute to the prismatic colors of Yellowstone National Park’s hot springs

Principle of Catalase Test

The principle of the catalase test is based on the rapid detection of catalase presence, which becomes evident by the formation of copious gas bubbles. Catalase positive organisms can detoxify the toxic effect of H2O2 by the catalytic activity of catalase.

Oppositely, catalase-negative microorganisms cannot decompose H2O2 as they lack catalase. The catalase test involves the mixing of inoculum with hydrogen peroxide. If the test organisms contain catalase, they can easily degrade H2O2 into H2O and O2 (in the form of bubbles). There will be no formation of gas bubbles if a test organism lacks catalase.

Test Reagent

The catalase test only uses a single reagent (hydrogen peroxide). 3% of hydrogen peroxide is needed to check the presence of catalase in aerobically cultured bacteria. 15% of hydrogen peroxide is required to check the presence of catalase in an anaerobically cultured test organism.

  • To prepare a 3% solution of H2O2: Dissolve 3 grams of hydrogen peroxide in 100 ml of distilled water.
  • Similarly, for the preparation of a 15% solution of H2O2: Dissolve 15 grams of hydrogen peroxide in 100 ml of distilled water.


The catalase test can be performed by two standard methods, namely the tube and slide method.

Tube Method

It involves the following sequential steps:

  1. First, sterilize the test tubes by either using an autoclave or a hot air oven.
  2. Then, pour 1-3 ml of hydrogen peroxide into the tubes under sterile conditions.
  3. After that, take 24 hours of bacterial inoculum via a sterilized inoculating loop.
  4. Dip the inoculating loop straight into the test tube containing H2O2
  5. Observe the tubes for instant bubbling.

Slide Method

It involves the following sequential steps:

  1. First, sterilize glass slides by either using an autoclave or a hot air oven.
  2. Then, take 24 hours old bacterial inoculum via a sterilized inoculating loop under sterile conditions.
  3. Prepare a bacterial smear over the glass slide.
  4. Add 1-2 drops of H2O2 to the top of the bacterial smear.
  5. Observe the glass slide for the formation of bubbles.

Test Results

Positive result: Formation of effervescences or copious gas bubbles occurs.
Example: Corynebacterium diphtheria, mycobacterium tuberculosis, Rhodococcus equi, Staphylococcus sp, Listeria sp etc.

Negative result: There will be no formation of oxygen bubbles.
Example: Streptococcus sp, Enterococcus sp etc.

Uses of Catalase Test

  • The catalase test marks the existence of the catalase enzyme in the microbial sample.
  • It differentiates the catalase-positive and catalase-negative organisms relative to their genera as well as speciation.
  • It also uses as a possible method in identifying and differentiating different organisms belonging to the Enterobacteriaceae family.
  • The catalase test also distinguishes between the aerobic and obligate anaerobic bacteria based on the production of catalase enzyme.
  • It also differentiates between the aerotolerant strains of Clostridium sp (non-catalase producers) from the Bacillus sp (catalase producers).

Limitations of Catalase Test

  • To perform a catalase test, a test organism incubated for 18 to 24 hours should be used.
  • Hydrogen peroxide should be freshly prepared to perform the experiment, as it is a volatile compound.
  • Test organism inoculated from the blood agar media frequently gives false-positive results, as the RBCs are catalase-positive cells.

Therefore, the catalase test is a prevalent method to differentiate between different groups (aerobic and anaerobic), species based on the production of catalase enzyme.

Evolutionary Significance of Obligate Anaerobes

The existence of obligate anaerobes is a significant clue in the theory of the origins of life on planet Earth. While our atmosphere has a significant amount of oxygen now, that may not have always been the case. The presence of obligate anaerobes today suggests that the atmosphere once had much less oxygen, allowing bacteria to survive without oxygen facilitating enzymes. The theory suggests that with the rise of photosynthetic organisms, there also came a rise in the level of oxygen in the environment.

Aerotolerant anaerobe

Aerotolerant anaerobes use fermentation to produce ATP. They do not use oxygen, but they can protect themselves from reactive oxygen molecules. In contrast, obligate anaerobes can be harmed by reactive oxygen molecules.

There are three categories of anaerobes. Where obligate aerobes require oxygen to grow, obligate anaerobes are damaged by oxygen, aerotolerant organisms cannot use oxygen but tolerate its presence, and facultative anaerobes use oxygen if it is present but can grow without it.

Most aerotolerant anaerobes have superoxide dismutase and (non-catalase) peroxidase but don't have catalase. [1] More specifically, they may use a NADH oxidase/NADH peroxidase (NOX/NPR) system or a glutathione peroxidase system. [2] An example of an aerotolerant anaerobe is Propionibacterium acnes. [3]

  1. ^ WI, Kenneth Todar, Madison. "Nutrition and Growth of Bacteria".
  2. ^
  3. Zotta, T. Parente, E. Ricciardi, A. (2017). "Aerobic metabolism in the genus Lactobacillus: impact on stress response and potential applications in the food industry". Journal of Applied Microbiology. 122 (4): 857–869. doi: 10.1111/jam.13399 .
  4. ^
  5. Achermann, Y Goldstein, EJ Coenye, T Shirtliff, ME (July 2014). "Propionibacterium acnes: from commensal to opportunistic biofilm-associated implant pathogen". Clinical Microbiology Reviews. 27 (3): 419–40. doi:10.1128/CMR.00092-13. PMC4135900 . PMID24982315.

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In his letter of 14 June 1680 to The Royal Society, Antonie van Leeuwenhoek described an experiment he carried out by filling two identical glass tubes about halfway with crushed pepper powder, to which some clean rain water was added. Van Leeuwenhoek sealed one of the glass tubes using a flame and left the other glass tube open. Several days later, he discovered in the open glass tube 'a great many very little animalcules, of divers sort having its own particular motion.' Not expecting to see any life in the sealed glass tube, Van Leeuwenhoek saw to his surprise 'a kind of living animalcules that were round and bigger than the biggest sort that I have said were in the other water.' The conditions in the sealed tube had become quite anaerobic due to consumption of oxygen by aerobic microorganisms. [4]

In 1913 Martinus Beijerinck repeated Van Leeuwenhoek's experiment and identified Clostridium butyricum as a prominent anaerobic bacterium in the sealed pepper infusion tube liquid. Beijerinck commented:

'We thus come to the remarkable conclusion that, beyond doubt, Van Leeuwenhoek in his experiment with the fully closed tube had cultivated and seen genuine anaerobic bacteria, which would happen again only after 200 years, namely about 1862 by Pasteur. That Leeuwenhoek, one hundred years before the discovery of oxygen and the composition of air, was not aware of the meaning of his observations is understandable. But the fact that in the closed tube he observed an increased gas pressure caused by fermentative bacteria and in addition saw the bacteria, prove in any case that he not only was a good observer, but also was able to design an experiment from which a conclusion could be drawn.' [4]

For practical purposes, there are three categories of anaerobe:

  • Obligate anaerobes, which are harmed by the presence of oxygen. [5][6] Two examples of obligate anaerobes are Clostridium botulinum and the bacteria which live near hydrothermal vents on the deep-sea ocean floor.
  • Aerotolerant organisms, which cannot use oxygen for growth, but tolerate its presence. [7]
  • Facultative anaerobes, which can grow without oxygen but use oxygen if it is present. [7]

However, this classification has been questioned after recent research showed that human "obligate anaerobes" (such as Finegoldia magna or the methanogenic archaea Methanobrevibacter smithii) can be grown in aerobic atmosphere if the culture medium is supplemented with antioxidants such as ascorbic acid, glutathione and uric acid. [8] [9] [10] [11]

Some obligate anaerobes use fermentation, while others use anaerobic respiration. [12] Aerotolerant organisms are strictly fermentative. [13] In the presence of oxygen, facultative anaerobes use aerobic respiration without oxygen, some of them ferment some use anaerobic respiration. [7]

Fermentation Edit

There are many anaerobic fermentative reactions.

Fermentative anaerobic organisms mostly use the lactic acid fermentation pathway:

The energy released in this reaction (without ADP and phosphate) is approximately 150 kJ per mol, which is conserved in generating two ATP from ADP per glucose. This is only 5% of the energy per sugar molecule that the typical aerobic reaction generates taking advantage of the high energy of O2. [14]

Plants and fungi (e.g., yeasts) in general use alcohol (ethanol) fermentation when oxygen becomes limiting:

The energy released is about 180 kJ per mol, which is conserved in generating two ATP from ADP per glucose.

Anaerobic bacteria and archaea use these and many other fermentative pathways, e.g., propionic acid fermentation, butyric acid fermentation, solvent fermentation, mixed acid fermentation, butanediol fermentation, Stickland fermentation, acetogenesis, or methanogenesis.

Since normal microbial culturing occurs in atmospheric air, which is an aerobic environment, the culturing of anaerobes poses a problem. Therefore, a number of techniques are employed by microbiologists when culturing anaerobic organisms, for example, handling the bacteria in a glovebox filled with nitrogen or the use of other specially sealed containers, or techniques such as injection of the bacteria into a dicot plant, which is an environment with limited oxygen. The GasPak System is an isolated container that achieves an anaerobic environment by the reaction of water with sodium borohydride and sodium bicarbonate tablets to produce hydrogen gas and carbon dioxide. Hydrogen then reacts with oxygen gas on a palladium catalyst to produce more water, thereby removing oxygen gas. The issue with the GasPak method is that an adverse reaction can take place where the bacteria may die, which is why a thioglycollate medium should be used. The thioglycollate supplies a medium mimicking that of a dicot, thus providing not only an anaerobic environment but all the nutrients needed for the bacteria to thrive. [15]

Recently, a French team evidenced a link between redox and gut anaerobes [16] based on clinical studies of severe acute malnutrition. [17] These findings led to the development of aerobic culture of "anaerobes" by the addition of antioxidants in the culture medium. [18]

Few multicellular life forms are anaerobic, since only O2 with its weak double bond can provide enough energy for complex metabolism. [14] Exceptions include three species of Loricifera (< 1 mm in size) and the 10-cell Henneguya zschokkei. [19]

In 2010 three species of anaerobic loricifera were discovered in the hypersaline anoxic L'Atalante basin at the bottom of the Mediterranean Sea. They lack mitochondria which contain the oxidative phosphorylation pathway, which in all other animals combines oxygen with glucose to produce metabolic energy, and thus they consume no oxygen. Instead these loricifera derive their energy from hydrogen using hydrogenosomes. [20] [3]