Understanding Aerobes: Definition, Examples, and Their Role in Life
Aerobic organisms or aerobes meaning can grow in an oxygenated environment. The organism which can survive in the absence of oxygen is known as anaerobes. Anaerobes can grow only in the absence of oxygen are either obligate anaerobes or strict anaerobes. As per the research of marine biologists in July 2020, aerobic microorganisms in quasi-suspended animation were widely found in organically poor sediments. Those organisms are living at 250 feet below the seafloor of ages are up to 101.5 million years.
Types of Aerobes
Microorganisms like bacteria are usually classified into different groups depending on their characteristics such as physical appearance, nutrient and energy, culture properties, optimal growth temperature, oxygen requirement, biosynthetic capacity..etc. They are broadly classified into two types based on their oxygen requirements. They are aerobes and anaerobes. Based on the method of consuming oxygen, the aerobes are classified into three types. They are listed below.
Obligate aerobes
Facultative anaerobes
Microaerophiles
Aerotolerant anaerobes
Obligate Aerobes: The obligate aerobic bacteria definition requires free oxygen to survive. While undergoing cellular respiration, these organisms use oxygen for the metabolism process like sugar or fats to generate energy. During this type of respiration, oxygen will serve as the terminal electron acceptor for the electron transport chain. The advantage of aerobic respiration is it can yield more energy than anaerobic respiration or fermentation process. But the obligate aerobes undergo a high level of oxidative stress. The obligate aerobes get harmed due to reactive oxygen molecules. Examples of obligate aerobes are fungi and bacteria. The list of bacterias includes Mycobacterium tuberculosis, Pseudomonas aeruginosa, Bacillus, and Nocardia asteroides.
Streptomyces coelicolor is a gram-positive bacterium, belongs to the phylum Actinobacteria. This is known as a unique obligate aerobe because the genome of this aerobe bacterium encodes by numerous enzymes with its functions. It usually attributes to anaerobic metabolism in facultative and strictly anaerobic bacteria.
Facultative Anaerobes: A facultative anaerobes can synthesize energy through aerobic respiration in the presence of oxygen. Also, it has the capability to switch to the fermentation process for synthesizing energy in the absence of oxygen. Example of facultative anaerobes are bacterias namely Staphylococcus spp, Salmonella, Escherichia coli, Listeria spp, Shewanella oneidensis, and Yersinia pestis, and certain eukaryotic organisms like Saccharomyces cerevisiae
Microaerophiles: The microorganism under the microaerophiles, requires oxygen for survival, but it became toxic while exploring the atmospheric concentration of oxygen. That is the atmospheric air contains 21% of the oxygen. Many microaerophiles are also capnophiles, which require an elevated concentration of carbon dioxide. Examples of microaerophiles are Campylobacter, Helicobacter pylori...etc.
Function of Aerobes
Respiration is the important source of cells to convert fuel into energy. The end product of the respiration process is adenosine triphosphate (ATP), which uses the energy stored in phosphate bands to power chemical reactions. ATP is known as the currency of the cells. As oxygen is an excellent electron acceptor for generating ATP chemical reaction. Aerobic respiration can procedure more ATP while comparing to anaerobic respiration. The oxidation of glucose is a good example of aerobic respiration.
C₆H₁₂O₆ + 6O₂ + 38 ADP + 38 phosphate → 6 CO₂ + 44 H₂O + 38 ATP
The energy released during the above reaction is about 2880kJ per mol, During this process, every 38 ADP get conserved and regenerated into 38 ATP molecules per glucose. This is 19 times more energy per sugar molecule than the ATP generated in an anaerobic reaction. During the oxidation of glucose and water, oxygen is used during oxidation. The above reaction is the combined form of three series of biochemical reactions glycolysis, oxidative phosphorylation, and Krebs cycle.
Difference Between Aerobes and Anaerobes
Oxygen is an important molecule for the metabolism, survival, and growth of many microorganisms. Some organisms cannot survive in the presence of oxygen, and some organisms can survive without oxygen. The highly reactive molecules are such as hydrogen peroxide and superoxide free radicals are formed during the biochemical reactions involving oxygen. This causes harm to the organisms. In order to fight against the harmful effect of molecules, the enzymes in bacteria can convert free radicals into oxygen compounds such as water, microbes, possess enzymes, aerobes, peroxidase, and superoxide dismutase for oxygen metabolism. The anaerobes do not produce any enzymes to convert free radicals. So, it cannot survive in the presence of oxygen.
The aerobic bacteria meaning, it requires oxygen for the growth and survival of organisms.
The anaerobic bacteria definition does not require oxygen for its survival. The anaerobes use acetone, sulfur carbon dioxide as a final electron acceptor during energy metabolism.
The anaerobes are classified into two classes. They are listed below,
Aerotolerant anaerobes
Obligate anaerobes
Aerotolerant Anaerobe: The microorganisms under the classification of aerotolerant anaerobes will produce ATP using fermentation reaction without using oxygen. But they will use reactive oxygen molecules to protect themselves.
Obligate Anaerobes: These microorganisms cannot survive once it is explored to the environment oxygen, which contains 21% of oxygen. Oxygen tolerance varies from species to species. Some species can survive up to 8% of oxygen, while other organisms lose their vulnerability even at the 0.5% concentration of oxygen.
Using certain biochemical reactions, the bacteria are classified based on their oxygen requirements. The redox reaction indicator dyes adding to the other media can determine unknown bacterium can utilize oxygen. To demonstrate the anaerobic conditions and oxygen utilization, resazurin dye is used. This indicates the oxygen reduction reaction by changing the colour from blue to pink. Here, colour change intensity is associated with the oxygen requirement of the bacteria present in the medium. These methods are usually followed to demonstrate milk’s anaerobic condition.
Some researchers found some problems in conducting conventional techniques to determine the oxygen requirement of bacteria. These anaerobic bacteria are highly sensitive to the oxygen environment. But new technologies with sequencing technologies can be used to determine the oxygen requirement and other biochemical characteristics to support the growth of bacteria.
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FAQs on What Are Aerobes? Types, Functions & Biological Significance
1. What is an aerobe? Provide some examples.
An aerobe is an organism that requires an oxygenated environment to live and grow. These organisms use molecular oxygen (O₂) for cellular respiration, a process that efficiently converts nutrients into energy (ATP). Many life forms, from complex animals to simple microorganisms, are aerobes. Common examples include humans, most animals, and specific bacteria like Mycobacterium tuberculosis (which causes tuberculosis) and Nocardia species.
2. How are aerobes different from anaerobes?
The primary difference between aerobes and anaerobes lies in their relationship with oxygen. Aerobes depend on oxygen to carry out metabolic functions and cannot survive without it. In contrast, anaerobes do not require oxygen for survival and growth. In fact, for some anaerobes, known as obligate anaerobes, oxygen is toxic. Aerobic respiration yields significantly more energy (ATP) than anaerobic respiration, making it a more efficient metabolic pathway.
3. What are the main types of aerobes based on their oxygen requirements?
Aerobes can be classified into different types based on how they interact with oxygen:
- Obligate Aerobes: These organisms strictly require oxygen to survive as they cannot perform anaerobic respiration or fermentation. Example: Pseudomonas aeruginosa.
- Facultative Anaerobes: These are adaptable organisms that can switch between aerobic respiration (if oxygen is present) and anaerobic respiration or fermentation (if oxygen is absent). Example: E. coli, Yeast.
- Microaerophiles: These organisms require oxygen but at concentrations lower than what is found in the atmosphere (typically 2-10%). High oxygen levels can be toxic to them. Example: Helicobacter pylori.
- Aerotolerant Anaerobes: These organisms do not use oxygen for metabolism but are not harmed by its presence. They exclusively use anaerobic respiration or fermentation.
4. Why is oxygen so essential for the survival of an obligate aerobe?
Oxygen is essential for an obligate aerobe because it acts as the final electron acceptor in the electron transport chain (ETC) during aerobic respiration. This process allows the organism to generate a large amount of ATP (energy currency of the cell). Without oxygen, the ETC halts, and the organism cannot produce sufficient energy to maintain its life processes, leading to its death. They lack the metabolic pathways for fermentation or anaerobic respiration to generate energy in an oxygen-deprived environment.
5. Can an organism be both an aerobe and an anaerobe?
Yes, an organism that can function as both an aerobe and an anaerobe is called a facultative anaerobe. These organisms are metabolically flexible. They prefer to use oxygen for aerobic respiration because it yields more energy. However, if oxygen is not available, they can switch to alternative pathways like fermentation or anaerobic respiration to survive. A classic example is yeast (Saccharomyces cerevisiae), which performs aerobic respiration in the presence of oxygen and fermentation (producing alcohol) in its absence.
6. What is the importance of aerobic bacteria in our ecosystem?
Aerobic bacteria play a crucial role in the ecosystem. Their importance includes:
- Decomposition: They are primary decomposers, breaking down dead organic matter and recycling essential nutrients like carbon and nitrogen back into the environment.
- Bioremediation: Many aerobic bacteria are used in cleaning up environmental pollutants. They can metabolise and break down harmful substances like petroleum hydrocarbons and pesticides into less toxic compounds.
- Wastewater Treatment: In sewage treatment plants, aerobic bacteria are used in the aeration tanks to decompose organic waste, purifying the water.
7. How does a facultative anaerobe differ from an aerotolerant anaerobe?
The key difference is in their metabolic response to oxygen. A facultative anaerobe can use oxygen if it's present (via aerobic respiration) but can also grow without it (via fermentation/anaerobic respiration). It actively switches its metabolic pathway. An aerotolerant anaerobe, on the other hand, never uses oxygen for its metabolism; it only uses fermentation or anaerobic respiration. It simply tolerates the presence of oxygen without being harmed, but it does not gain any metabolic benefit from it.
