Definition of an anaerobic organism
Anaerobic organisms are those that live in an anoxic environment – an environment that lacks oxygen. While most living things require oxygen to survive, aerobic oxygen can actually be toxic to anaerobic organisms.
The vast majority of organisms produce energy molecules called ATP (adenosine triphosphate) through a process of aerobic cellular respiration. These complex chemical interactions take place in the cytoplasm and cell membrane of prokaryotes and in the mitochondria of eukaryotes.
During respiration, oxygen acts as the final electron acceptor at the end of an electron transport chain, which is why aerobic organisms must breathe oxygen-rich air to survive. However, anaerobic organisms use either fermentation or anaerobic cellular respiration to produce ATP. In this case, an atom other than oxygen is the final electron acceptor.
For example, some anaerobic bacteria that live deep in the mud in swampy areas use a sulfate ion instead of oxygen, and the by-product is hydrogen sulfide instead of water. This explains the sulphurous smell in many swamps and mud flats.
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 there is a lack of oxygen, they can switch to anaerobic respiration or fermentation. In contrast, obligate anaerobes must live without oxygen. They are only equipped for anaerobic respiration or fermentation, and the presence of oxygen kills them.
Facultative anaerobes
Human muscle cells are facultative anaerobes. During exercise where a person gets a lot of oxygen to their muscles, such as B. long-distance running, the cells are subjected to aerobic respiration. But during high-intensity exercise like sprinting, when the body’s demand for oxygen exceeds the lungs’ ability to provide it, muscle cells 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 often felt during strenuous exercise. Because this is so much less efficient, a person can only engage in such an intense activity for a very short period of time before they “hit the wall” and have to stop.
Another well-known facultative anaerobes are the bacterium Escherichia coli. While E.coli has had a bad rap in the press due to foodborne illness incidents, E.coli is actually very important and beneficial to residents of the human gastrointestinal tract.
They aid in the digestion of food and the absorption of necessary vitamins, as well as protection from potentially harmful infections. These bacteria can easily function with or without oxygen, making them highly adaptable to different environments.
In the anaerobic intestine, they use fermentation to generate energy. When found in the oxygen-rich environment outside of 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 the processing of many types of cheese.
Obligatory anaerobes
A notorious example of an obligate anaerobe is Clostridium botulinum. This widespread bacterium produces a potent neurotoxin that can be deadly even in small amounts. It grows in products like homemade preserves, 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. As conditions improve, the bacteria begin to grow and produce potentially deadly toxins.
If a person consumes food contaminated with actively growing C. botulinum, they are likely to succumb to a fatal 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 breathing and possible death by suffocation. Infantile botulism occurs after a baby ingests C. botulinum spores, which can be found in soil, dust, or honey.
For this reason, honey should never be given to young babies; Before the age of one year, their immune system is not strong enough to deal with the spores, so they start to grow and cause serious diseases.
Possibly the largest concentration of obligate anaerobes on the planet resides on the deep-sea floor, where they inhabit hydrothermal vents. Erupting from the earth’s crust, these hot underwater springs are loaded with minerals that the bacteria use to fuel their chemosynthetic process, thereby building organic molecules.
First discovered by researchers of the Galapagos Islands in 1977, its existence rewrote all biology textbooks. Until then, it was thought that photosynthesis was the only means by which autotrophic organisms could convert energy into food for themselves.
Bob Ballard, the deep-sea explorer who discovered the Titanic wreck, was on the day the submersible Alvin went down to film the vents. He later said that the discovery of chemosynthesis in Vent bacteria was one of the greatest biological discoveries of the 20th century – far more important than any historical wreck. Evolutionists speculate that life began on the deep ocean floor, fueled by chemosynthesis.
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
Anaerobes: friend or foe?
It is clear that our planet is well populated with various anaerobic organisms. Some are pathogenic and cause serious infections such as MRSA, botulism, and tetanus. Others are useful, adding beauty to hot springs, flavoring cheeses, and shaping the communities of the ocean.
For others, like E. coli, their status depends on their location: while E. coli is a necessary, helpful resident of the human gut, it can become pathogenic when ingested orally or otherwise. In summary, anaerobes are important inhabitants of the earth, excellently filling their ecological niches.
