What is Facultative Anaerobe?
Anaerobes are microorganisms that can survive in the lack of free oxygen; obligatory, also known as stringent microbes are anaerobes that can only survive in the anaerobic environment. Some species, known as facultative anaerobes, can support the growth both in the presence or absence of free oxygen. Microaerophiles, on the other hand, are organisms that thrive in low oxygen environments. Let us see the facultative anaerobe definition that will help us in understanding the concept of the facultative anaerobe and facultative anaerobic process.
Facultative anaerobe definition in biology, a microbe that can produce energy via aerobic respiration but then shift to anaerobic respiration based on the quantity of oxygen and fermentable content present in the environment. The facultative anaerobes examples include E. Coli and yeast. The article focuses on the discussion of the facultative anaerobe definition, facultative anaerobes examples. Ecological Importance of Facultative Anaerobes and a comparative study between the obligate anaerobes vs facultative anaerobe is also mentioned in the article.
What is Aerobic and Anaerobic Respiration?
Let us briefly understand what is aerobic and anaerobic respiration to develop the understanding of facultative anaerobic bacteria. Aerobic respiration is the process of breaking down glucose in the presence of oxygen in order to generate energy in the form of compounds like ATP. The cascade of reactions is catalyzed by enzymes can be defined as aerobic respiration.
The method entails the movement of electrons between compounds that serve as a source of the substrate, such as glucose, to oxygen, which serves as the terminal electron acceptor. Aerobic respiration is the most important mechanism for generating energy. Finally, this strategy offers ATP and metabolic intermediates for a variety of additional cell pathways, including carbohydrate, lipids, and protein synthesis.
The chemical equation mentioned below will help in better understanding the concept.
\[ C_6H_{12}O_6 + 6O_2 \rightarrow Energy + 6H_{2}O + 6CO_{2}\]
Anaerobic respiration is differentiated from that of aerobic respiration with respect to the requirement of oxygen while converting the given substrate such as glucose into energy.
The breakdown of glucose in the absence of oxygen to produce energy is called anaerobic respiration. Some bacteria have evolved a system that uses oxygen-containing salts as an electron acceptor rather than free oxygen. The energy produced by anaerobic respiration is useful when there is a high demand for energy. However, when compared to aerobic respiration, it is produced in much smaller amounts.
The chemical reaction mentioned below will help in understanding the concept of anaerobic respiration.
\[ C_6H_{12}O_{6} + 6O_{2} \rightarrow 2C_3H_{6}O_3 + Energy \]
Facultative Anaerobic Bacteria
The facultative anaerobic bacteria are those bacteria that can survive and grow in both aerobic and anaerobic conditions. One of the common facultative anaerobes examples in the bacterial category is E.coli. Enterobacteriaceae, Vibrionaceae, and Pasteurellaceae are the three major families of facultative anaerobic bacteria.
Since the facultative anaerobic bacteria can perform respiration in both conditions there are three cellular pathways for energy production of these microbes, they are aerobic respiration, anaerobic respiration, and fermentation. As we have already discussed the anaerobic and aerobic respiration, let us understand fermentation.
Fermentation is the process by which large and complex organic acids and sugar molecules are broken down into a simpler form that can be utilized to generate chemical energy. Chemical energy, usually in the form of ATP, is crucial because it powers a variety of biological functions. Fermentation is seen in obligate anaerobes and facultative anaerobe because it does not consume oxygen. Another key aspect to remember is that the electrons are not passed through the electron transport chain system to the ultimate electron acceptor. An organic compound, such as pyruvate in lactic acid fermentation or acetaldehyde in alcohol fermentation, serves as the final electron acceptor.
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Facultative Anaerobes Examples
As we have seen the facultative anaerobe definition and the basis n which these classifications are made let us look into some examples. Enterobacteriaceae, Vibrionaceae, and Pasteurellaceae constitute the major families of facultative anaerobic bacteria.
Facultative anaerobes examples from the Enterobacteriaceae family
E.coli
Klebsiella pneumoniae
Proteus mirabilis
Shigella
Salmonella
Yersinia pestis
Facultative anaerobes examples from the Vibrionaceae family
Vibrio
Aeromonas
Photobacterium
Facultative anaerobes examples from the Pasteurellaceae
Pasteurella and Haemophilus
Obligate anaerobes vs facultative anaerobe
Since we have understood the facultative anaerobe, let us have a comparative study about the obligate anaerobes vs facultative anaerobe.
Difference Between Obligate Anaerobes Vs Facultative Anaerobe
Ecological Importance of Facultative Anaerobes
Facultative anaerobes have played a critical role in the preservation and continuation of the global reserve of life's key elements, namely carbon, nitrogen, and sulphur, as well as the breakdown of complex molecules. Because facultative anaerobes can survive in a variety of environments, including those with and without oxygen. Alternative substrates for metabolism are used by these creatures, such as nitrogen, sulphur, and iron, which have all been part of various biogeochemical cycles on the planet that have led to the evolution of life, thus helping in the preservation of global resources. The facultative anaerobes are used as an alternative to producing biofuels, these organisms are also used in the process of water purification in the wastewater treatment process.
In conclusion of the article, we have learned about facultative anaerobes, their definition example, and the mode of respiration. We have also learned about the difference between obligate anaerobes vs facultative anaerobe.
FAQs on Facultative Anaerobes
1. What exactly is a facultative anaerobe?
A facultative anaerobe is a versatile organism, typically a bacterium or yeast, that can produce energy and grow in both the presence and absence of oxygen. When oxygen is available, it performs aerobic respiration, which is highly efficient. When oxygen is absent, it switches to a less efficient process like fermentation or anaerobic respiration to survive. This metabolic flexibility allows it to thrive in diverse environments.
2. What are some common examples of facultative anaerobes?
Facultative anaerobes are found across different kingdoms. Some common examples include:
- Escherichia coli (E. coli): A bacterium commonly found in the lower intestine of warm-blooded organisms.
- Saccharomyces cerevisiae: The species of yeast used in baking and brewing.
- Staphylococcus aureus: A bacterium that is part of the normal skin flora but can also cause infections.
- Listeria monocytogenes: A pathogenic bacterium that can be found in contaminated food.
- Enterococcus faecalis: A Gram-positive bacterium that inhabits the human gastrointestinal tract.
3. Is yeast a facultative anaerobe, and how does this relate to baking?
Yes, yeast (specifically Saccharomyces cerevisiae) is a classic example of a facultative anaerobe. In baking, when yeast is mixed into dough, it first uses the trapped oxygen for aerobic respiration, producing carbon dioxide and water. As the oxygen runs out, it switches to alcoholic fermentation. This anaerobic process produces more carbon dioxide, which makes the dough rise, and also ethanol, which mostly evaporates during baking.
4. How does a facultative anaerobe's energy production change with and without oxygen?
A facultative anaerobe's method of energy (ATP) production changes dramatically based on oxygen availability:
- With Oxygen: It uses aerobic respiration. Glucose is completely broken down through glycolysis, the Krebs cycle, and the electron transport chain, with oxygen acting as the final electron acceptor. This process is very efficient, yielding approximately 36-38 ATP molecules per glucose molecule.
- Without Oxygen: It switches to fermentation or anaerobic respiration. Glycolysis still occurs, but the subsequent steps only serve to regenerate NAD+ so glycolysis can continue. This process is far less efficient, yielding only 2 ATP molecules per glucose molecule.
5. What is the key difference between a facultative anaerobe and an obligate anaerobe?
The key difference lies in their relationship with oxygen. A facultative anaerobe can grow with or without oxygen but grows better with it because aerobic respiration yields more energy. In contrast, an obligate anaerobe cannot survive in the presence of oxygen. Oxygen is toxic to them because they lack the necessary enzymes, like catalase and superoxide dismutase, to break down harmful byproducts of oxygen metabolism.
6. Why would a facultative anaerobe prefer to grow in an environment with oxygen if it can survive without it?
A facultative anaerobe prefers growing with oxygen due to energy efficiency. Aerobic respiration generates up to 19 times more ATP (energy currency of the cell) from a single glucose molecule compared to fermentation. This large energy surplus allows the organism to grow faster, reproduce more quickly, and perform cellular functions more effectively. The ability to survive without oxygen is a crucial adaptation for environments where oxygen is scarce, but it is a much lower-energy mode of living.
7. Where are facultative anaerobes important in the human body and the environment?
Facultative anaerobes play critical roles in various ecosystems:
- In the Human Body: The human gut is a prime example of an environment with fluctuating oxygen levels. Facultative anaerobes like E. coli thrive here, helping to maintain gut health by consuming any available oxygen, thereby creating a suitable anaerobic environment for the beneficial obligate anaerobes.
- In the Environment: They are abundant in soil, water, and aquatic sediments, where they are essential for nutrient cycles like the nitrogen cycle.
- In Food Industry: Species like yeast and some lactic acid bacteria are used to produce bread, cheese, yoghurt, and alcoholic beverages through controlled fermentation processes.
