In biochemistry, anaerobic metabolism is one the most studied concepts and this piece is going to focus on discussing it. It is a kind of metabolism in which other electron acceptors (also called oxidizers or oxidizing agents) except for molecular oxygen are used. Even though the oxygen itself is not going to be the final acceptor of electrons, the mechanism still utilizes a metabolic electron transport chain.
This is not the same with aerobic organisms that have metabolic processes, where electrons are transported to the electron transport chain, and as expected, the final acceptor of electrons is oxygen. A lot of energy is involved with molecular oxygen when used as an oxidizing agent and that is what makes it a first-class electron acceptor.
Anaerobes make use of other weaker oxidizers like fumarate, sulfur, sulfate compounds, and nitrate. These are all classified as terminal acceptors of electrons and their reduction potentials are much lower than when compared with oxygen. What this implies is that a lower level of energy is released for each molecule that has been oxidized. Hence, the efficiency of anaerobic is remarkably lower than aerobic versions.
Importance of Anaerobic Metabolism
Even though anaerobic metabolism is not at the same level as the aerobic versions, it has a lot of important applications. A good example of this is that anaerobic metabolism is a crucial part of the sulfur, nitrogen, carbon, and iron cycles in nature. This is made possible via the decrease of the oxy-anions of carbon, sulfur, and nitrogen to compounds that are more reduced.
The cycling of all these various compounds can only be done via processes of anaerobic metabolism and it has its effects on global warming and the carbon cycle. This form of metabolism is seen in different natural habitats. These include the soil, subterranean spaces, freshwater sediments, aquifers, biofilms, and others. These environments, like the soil, have oxygen that contains micro-environments that do not have oxygen as a result of the reduced diffusion of the features of gaseous oxygen.
A common illustration here regarding the importance of anaerobic metabolism to the global ecology will be the utilization of nitrate in the form of a terminal acceptor of electrons or denitrification, and this is the principal way via which fixed nitrogen is recycled right to the natural air in the form of nitrogen gas in molecules. This process of denitrification is needed in the interactions between hosts and the microbes.
Examples of Anaerobic Metabolism
Now that explanation has been given for anaerobic metabolism, it is good to give illustrations or further details. This process is often compared with the presence of mitochondria in microorganisms that depend on oxygen, but the real equivalent is with anaerobic ciliates that make use of denitrifying organisms to increase their energy profile.
Another illustration here is the one referred to as methanogenesis, which is a kind of carbon dioxide respiration and is utilized for the production of methane gas via anaerobic digestion. The biogenic methane is also utilized as a reliable alternative to crude oils which have a severe impact on our planet today. However, it must be said that excessive production of biogenic methane as seen in landfills is inimical.
This is because they end up releasing massive quantities of methane into the atmosphere – methane is a very powerful example of greenhouse gases and it has its impact on the climate. There is also sulfate-based respiration which releases compounds like hydrogen sulfide, known for its horrible smell in the wetlands. This compound can react with the heavy metals found in the solution and that causes the formation of sulfide-containing metal ores.
Anaerobic respiration is not just about ecological importance but also real-life economic applications. Denitrification has found wide usage when it comes to the removal of nitrites and nitrate from waste grounds.
An excessive fraction of nitrate can cause what is known as the eutrophication of the waterways that would later become the destination for treated water. Increased level of nitrite present in drinking water triggers problems because of the toxic elements. The process of denitrification transforms the compounds into gaseous nitrogen that does not contribute any harm or damage.
Particular examples of anaerobic metabolism will be the one referred to as bioremediation which utilizes microbes to transform dangerous chemicals into less dangerous molecules which can then be used for the cleaning up of water bodies like oceans, lakes, aquifers, and beaches. A way to illustrate this will be to consider dangerous selenate or arsenate compounds which can be relatively neutralize using anaerobic bacteria through anaerobic metabolism.
Even the reduction of other chlorinated compounds which are classified as chemical pollutants like carbon tetrachloride and vinyl chloride happens through anaerobic metabolism but this is not even the end of its economic relevance. It is also very helpful when it comes to the generation of electricity in microbial fuel cells.
This involves microorganisms that do metabolism via solid acceptors of electrons like oxidized iron involving the transfer of electrons from the reduced compounds to the electrode. The same mechanism here can also see the breakdown of organic carbon waste which can then be channeled towards the generation of electricity.
Comparison Anaerobic Metabolism with Fermentation
Some always manage to compare anaerobic metabolism with fermentation or even think that they are the same. However, the fact is that these two processes are far from being the same. The way both systems generate and use energy is different so they should not in any way be considered to be the same.
For metabolism in cells, both anaerobic and aerobic, there is a usage of chemical compounds that have undergone reduction. Fermentation, on the other hand, does not make use of an electrochemical gradient. It is a process that rather utilizes substrate-level phosphorylation for the generation of ATP.
In this instance, nicotinamide adenine dinucleotide (NAD) is the electron acceptor and it is produced from NADH created in the steps of the oxidation of the fermentation process via the reduction of compounds that have undergone oxidation. Even though the oxidized compounds are created during the pathway of fermentation but they can also be done with the influence of external substances.