Facultative anaerobe can utilize nitrate, nitrite, fumarate, elemental sulfur, or metal ions like iron or manganese as an electron acceptor when placed in an oxygen-deficient environment. As facultative organisms have the capacity to survive in oxygenated as well deoxygenated environments, the question is: which condition is preferable for their survival, aerobic or anaerobic?
Do facultative anaerobes grow better in oxygen or in the absence of oxygen? Well, facultative anaerobes may grow better in aerobic conditions based on the ATP yield.
To understand the transition of facultative anaerobes to aerobic respiration or vice versa, we need to have a basic understanding of the bioenergetic cycle involved in respiration, i. The generation of proton motive force pmf across the membrane due to the reduction of the electron acceptor substrate in the final step of the electron transport chain serves as the primary point for the generation of the ATP.
Eventually, pmf is involved in the ATP generation. In facultative anaerobes, the pmf generation takes place by a number of alternative pathways, as discussed below. Now, it is important to understand: What enzymes do facultative anaerobes have? Enzyme SOD eliminates the harmful superoxide anion by converting it into ground-state oxygen along with hydrogen peroxide. Thus eliminating or neutralizing destructive superoxide anions from the cell via the following chemical reaction.
The reaction product is hydrogen peroxide, which is an oxidizing agent. It has a tendency to diffuse out of the cell. However, many facultative anaerobes also have catalase enzymes, which further help to eliminate the hydrogen peroxide from the cell as well.
Catalase utilizes hydrogen peroxide as an oxidant electron acceptor as well as a reducing agent electron donor resulting in the formation of water and molecular oxygen. The most common examples of the facultative anaerobes are bacteria e. Many of the human pathogenic bacteria are facultative anaerobes, like Salmonella and P. Temperature, pH, and oxygen have always been the core environmental condition that has led to the evolution of life on earth.
Depending on these physical environmental conditions, organisms, especially prokaryotes , have been classified into various categories. In the current context, we will limit our classification based on the availability of oxygen. Based on the critical need for environmental oxygen, organisms can be classified into the following categories:.
These organisms mandatorily need molecular oxygen O 2 for their survival and growth. These organisms derive energy by aerobic respiration wherein they utilize O 2 as a final electron acceptor. Examples are Mycobacterium tuberculosis , Nocardia asteroids , etc. Based on the tolerance to the amount of oxygen, Obligate anaerobes can be categorized as:. In effect, for such organisms, O 2 is toxic, which can result in complete inhibition or killing of these organisms. These organisms derive their complete energy from fermentation or anaerobic respiration or bacterial photosynthesis, or methanogenesis.
Actinomyces, Bacteroides, Clostridium, etc are some of the anaerobic bacteria. Facultative anaerobe definition biology- The organisms which can survive in both oxygenated as well as the deoxygenated environment are known as facultative anaerobes. These are the most adaptable organisms that have the capability to switch between aerobic and anaerobic types of respiration. In anaerobic conditions i. Escherichia coli , Pseudomonas aeruginosa , Staphylococcus spp.
These are the bacteria that survive entirely on an anaerobic fermentative type of metabolism however, the presence of O 2 does not affect these organisms.
Thus, it can be said that these organisms are insensitive or tolerant to the presence of O 2. Such organisms completely derive energy from fermentation alone irrespective of the presence of environmental O 2. Examples are- Campylobacter jejuni , lactobacilli, and streptococci. Those organisms that need a low amount of O 2 for their survival i. These are different from aerotolerant organisms as these organisms need oxygen for their survival, however in extremely low amounts.
Some of the common examples are Actinomyces , Clostridium , Propionibacterium , Bifidobacterium , Bacteroides , Fusobacterium , Prevotella , etc. This is a simple test that can help to identify different kinds of bacteria, depending on their oxygen requirement. The difference in the behavior of different organisms in oxygenated and deoxygenated environment can be observed in vitro in the test tube by growing bacteria in thioglycolate culture media.
The sterilized thioglycolate medium permits complete motility of the test bacterium as it contains a low amount of agar. Sterilizing thioglycolate medium, which has strong reducing properties, removes oxygen from it. The sky is up. Gravity sucks. Nothing can travel faster than light. Multicellular life needs oxygen to live. Except we might need to rethink that last one. Scientists have just discovered that a jellyfish-like parasite doesn't have a mitochondrial genome - the first multicellular organism known to have this absence.
That means it doesn't breathe; in fact, it lives its life completely free of oxygen dependency. This discovery isn't just changing our understanding of how life can work here on Earth - it could also have implications for the search for extraterrestrial life.
Life started to develop the ability to metabolise oxygen - that is, respirate - sometime over 1. A larger archaeon engulfed a smaller bacterium, and somehow the bacterium's new home was beneficial to both parties, and the two stayed together.
That symbiotic relationship resulted in the two organisms evolving together, and eventually those bacteria ensconced within became organelles called mitochondria. Every cell in your body except red blood cells has large numbers of mitochondria, and these are essential for the respiration process. Eukaryotes can also undergo anaerobic respiration. Some examples include alcohol fermentation in yeast and lactic acid fermentation in mammals.
The fermentation method used by animals and certain bacteria like those in yogurt is called lactic acid fermentation. This type of fermentation is used routinely in mammalian red blood cells and in skeletal muscle that has an insufficient oxygen supply to allow aerobic respiration to continue that is, in muscles used to the point of fatigue.
The excess amount of lactate in those muscles is what causes the burning sensation in your legs while running. This pain is a signal to rest the overworked muscles so they can recover. In these muscles, lactic acid accumulation must be removed by the blood circulation and the lactate brought to the liver for further metabolism. The chemical reactions of lactic acid fermentation are the following:.
Lactic acid fermentation : Lactic acid fermentation is common in muscle cells that have run out of oxygen. The enzyme used in this reaction is lactate dehydrogenase LDH. The reaction can proceed in either direction, but the reaction from left to right is inhibited by acidic conditions. Such lactic acid accumulation was once believed to cause muscle stiffness, fatigue, and soreness, although more recent research disputes this hypothesis. Once the lactic acid has been removed from the muscle and circulated to the liver, it can be reconverted into pyruvic acid and further catabolized for energy.
Another familiar fermentation process is alcohol fermentation, which produces ethanol, an alcohol. The use of alcohol fermentation can be traced back in history for thousands of years.
The chemical reactions of alcoholic fermentation are the following Note: CO 2 does not participate in the second reaction :. Alcohol Fermentation : Fermentation of grape juice into wine produces CO2 as a byproduct. Fermentation tanks have valves so that the pressure inside the tanks created by the carbon dioxide produced can be released.
The first reaction is catalyzed by pyruvate decarboxylase, a cytoplasmic enzyme, with a coenzyme of thiamine pyrophosphate TPP, derived from vitamin B 1 and also called thiamine.
A carboxyl group is removed from pyruvic acid, releasing carbon dioxide as a gas.
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