The key difference between obligate aerobes and obligate anaerobes is that obligate aerobes cannot live without the presence of oxygen while obligate anaerobes cannot live in the presence of oxygen.
Microorganisms show great diversity since they are present everywhere. They react differently to molecular oxygen. There are six major groups of microorganisms based on the oxygen requirement: obligate aerobes, obligate anaerobe, facultative anaerobe, aerotolerant, microaerophile, and capnophile. Obligate aerobes or strict aerobes need oxygen to live and grow. They need a sufficient amount of oxygen to survive. In contrast, obligate anaerobes or strict anaerobes cannot live in the presence of oxygen. They are killed by oxygen.
What are Obligate Aerobes?
Obligate aerobes or strict aerobes are organisms that cannot grow without a sufficient supply of oxygen. Therefore, oxygen is absolutely essential for the survival and multiplication of obligate aerobes. They carry out aerobic respiration with a goal of oxidizing substrates in order to produce energy. Oxygen is used as the final electron acceptor, and they produce more energy than anaerobes.
All animals, plants, most fungi and some bacteria are obligate aerobes. Mycobacterium tuberculosis, Micrococcus luteus, Neisseria meningitides, N. gonorrheae, Pseudomonas aeruginosa, Nocardia spp, Legionellae, and Bacillus are several examples of obligate aerobic bacteria. Obligate aerobes are easy to grow in laboratory conditions. In a culture test tube, obligate aerobes grow near the surface.
What are Obligate Anaerobes?
Obligate anaerobes are a group of microorganisms that cannot survive in the presence of oxygen. Obligate anaerobes die due to oxygen poisoning. They don’t possess the enzymes such as superoxide dismutase and catalase which are necessary to convert lethal superoxide formed due to the presence of oxygen. When oxygen is present, all the functions occurring in the obligate anaerobes are stopped.
Obligate anaerobes do not require oxygen for respiration. They carry out anaerobic respiration or fermentation in order to produce energy. During anaerobic respiration, they use different types of molecules such as sulfate, nitrate, iron, manganese, mercury, or carbon monoxide as electron acceptors for respiration. Some examples of obligate anaerobic bacteria are Actinomyces, Bacteroides, Clostridium spp, Fusobacterium spp, Porphyromonas spp, Prevotella spp, Propionibacterium spp, and Veillonella spp.
These organisms are found in anaerobic environments such as deep sediments of soil, still waters, at the bottom of the deep ocean, the intestinal tract of animals and hot springs, etc. Moreover, obligate anaerobes are difficult to grow and study under laboratory conditions. Special equipment is needed to study obligate anaerobes. Anaerobic jar is one of the most commonly used equipment in obligate anaerobe studies. This equipment removes oxygen from the inner environment and fills it with carbon dioxide, which facilitates the growth of obligate anaerobes.
What is the Difference Between Obligate Aerobes and Obligate Anaerobes?
Obligate aerobes are organisms that require a sufficient amount of oxygen for the growth and multiplication while obligate anaerobes are organisms which live in an anaerobic environment, in the complete absence of oxygen. So, this is the key difference between obligate aerobes and obligate anaerobes. Obligate aerobes require the presence of abundant oxygen. In contrast, obligate anaerobes are killed in the presence of oxygen. Furthermore, obligate aerobes carry out aerobic respiration while obligate anaerobes show anaerobic respiration or fermentation.
Besides, another difference between obligate aerobes and obligate anaerobes is that in a culture test tube, obligate aerobes always grow very close to the surface of the culture tube while obligate anaerobes gather at the bottom of the culture tube.
Below is a summary tabulation of the difference between obligate aerobes and obligate anaerobes.
Summary – Obligate Aerobes vs Obligate Anaerobes
Obligate aerobes need abundant oxygen to grow and multiply. In contrast, obligate anaerobes live under the complete absence of oxygen. Molecular oxygen is poison for obligate anaerobes since all their metabolic functions cease in the presence of oxygen. Thus, this is the key difference between obligate aerobes and obligate anaerobes. In a culture tube, we can see obligate aerobic bacteria at the surface of the liquid medium while obligate anaerobes are at the bottom of the tube.
1. “Anaerobic” By Pixie – Own work (Public Domain) via Commons Wikimedia
2. “Clostridium perfringens” By CDC/Don Stalons – the Centers for Disease Control and Prevention’s Public Health Image Library (PHIL) (Public Domain) via Commons Wikimedia