- Some examples of anaerobic respiration
- Use of nitrates as an electron acceptor
- Sulfate as an electron acceptor
- Carbon dioxide as an electron acceptor
- Iron as an electron acceptor
- Organisms that can use multiple electron acceptors
- References
Anaerobic respiration is the respiratory process by which different microorganisms obtain energy and metabolize organic compounds while they are in the absence of molecular oxygen.
In aerobic respiration, oxygen acts as an electron receptor at the end of the electron transport chain. This chain is the process by which cells can generate energy.
Desulfovibrio desulfuricans, an organism that uses sulfates for anaerobic respiration
Organisms that carry out anaerobic respiration, mainly prokaryotic organisms, replace oxygen with other compounds that act as final acceptors in the electron transport chain.
Anaerobic respiration should not be confused with fermentation processes. In the latter, the electron acceptor ends up being an organic molecule that is not completely reduced and there is no electron transport chain as in respiration processes.
In anaerobic respiration, the electron acceptors at the end of the electron transport chain can be compounds such as sulfur, sulfates, nitrates and carbon dioxide, among others.
Some examples of anaerobic respiration
Use of nitrates as an electron acceptor
Some organisms of the genus Geobacter, such as G. metallireducens and G. sulphurreducens can use humic substances as electron donors and use nitrate and / or fumarate as electron acceptors.
In general, organisms that carry out this process reduce nitrates (# 3 -) to nitrites (# 2 -) through the enzyme nitrate reductase.
In turn, nitrites can be used as electron acceptors by other organisms.
Sulfate as an electron acceptor
Desulfovibrio desulfuricans is a sulfate reducing bacteria. These types of bacteria use sulfate as the final electron acceptor. Some species of the genus Clostridium also use sulfates in this way.
The use of sulfates (SO 4 2-) as an electron acceptor results in the production of sulfite ion (S 2-) or hydrogen sulfite (H 2 S).
In sulfur deposits, soils and fresh waters, it is common to find bacteria that use sulfates as an electron acceptor.
Carbon dioxide as an electron acceptor
Many of the methanogenic organisms, that is, that are responsible for the production of methane, use carbon dioxide as an electron acceptor.
Bacteria from the Methanobacterium, Methanococcus and Methanosarcina genera, among others, belong to this group.
It is common to find methanogenic organisms that use carbon dioxide as an electron acceptor in industrial anaerobic water treatment systems.
In these systems organisms that use sulfate as an electron acceptor are also common.
Iron as an electron acceptor
Other organisms can use the ferric ion as an electron acceptor. In this process the ferric ion (Fe 3+) is reduced to ferrous ion (Fe 2+).
This reduction is carried out by the enzyme iron reductase, present in organisms such as Geobacter metallireducens.
Organisms that can use multiple electron acceptors
Living organisms have a great capacity for adaptation, which has allowed many to use multiple electron acceptors.
This is the case of Anaeromyxobacter dehalogenans, a strain that can use as electron acceptors, compounds as different as nitrites, nitrates, iron, oxygen, fumarate and even uranium.
References
- Gerardi M. (2003). The mycrobiology of anaerobic digesters. John Wiley and Sons. New Jersey, USA
- Lovley D. et al. Humics as an electron donor for anaerobic respiration. Environmental Microbiology. 1999; 1 (1): 89-98
- Seifriz W. Anaerobic Respiration. Science, New Series. 1945; 101 (2613): 88-89
- Scott G. Anaerobic Respiration Vs. Fermentation. Science, New Series. 1945; 101 (2632): 585-586
- Wu Q. Sanford R. Löffler F. Uranium (VI) Reduction by Anaeromyxobacter dehalogenans Strain 2CP-C. Applied Environmental Microbiology. 2006; 72 (5): 3608-3614.