Anaerobic respiration

Anaerobic respiration

Anaerobic respiration is a form of fumarate are used. These terminal electron acceptors have smaller reduction potentials than O2, meaning that less energy is released per oxidized molecule. Anaerobic respiration is, therefore, in general energetically less efficient than aerobic respiration.

Anaerobic respiration is used mainly by obligate anaerobes meaning that they can respire only using anaerobic compounds and will die in the presence of oxygen.

Contents

  • Anaerobic respiration as compared with fermentation 1
  • Ecological importance 2
  • Economic relevance 3
  • Examples of respiration 4
  • See also 5
  • References 6
  • Bibliography 7

Anaerobic respiration as compared with fermentation

Cellular respiration (both aerobic and anaerobic) utilizes highly reduced species such as NADH and FADH2 (for example produced during glycolysis and the citric acid cycle) to establish an electrochemical gradient (often a proton gradient) across a membrane, resulting in an electrical potential or ion concentration difference across the membrane. The reduced species are oxidized by a series of respiratory integral membrane proteins with sequentially increasing reduction potentials with the final electron acceptor being oxygen (in aerobic respiration) or another species (in anaerobic respiration). The membrane in question is the inner mitochondrial membrane in eukaryotes and the cell membrane in prokaryotes. A proton motive force or pmf drives protons down the gradient (across the membrane) through the proton channel of ATP synthase. The resulting current drives ATP synthesis from ADP and inorganic phosphate.

Fermentation, in contrast, does not utilize an electrochemical gradient. Fermentation instead only uses substrate-level phosphorylation to produce ATP. The electron acceptor NAD+ is regenerated from NADH formed in oxidative steps of the fermentation pathway by the reduction of oxidized compounds. These oxidized compounds are often formed during the fermentation pathway itself, but may also be external. For example, in homofermentative lactic acid bacteria, NADH formed during the oxidation of glyceraldehyde-3-phosphate is oxidized back to NAD+ by the reduction of pyruvate to lactic acid at a later stage in the pathway. In yeast, acetaldehyde is reduced to ethanol to regenerate NAD+.

Ecological importance

Anaerobic respiration plays a major role in the global

  • Lawrence, Eleanor; Holmes, Sandra (1989), Henderson's dictionary of biological terms (10th ed.), University of Michigan: Wiley,  
  • Ralf, Cord-Ruwisch; H-J, Seitz; R, Conrad (1988), The capacity of hydrogenotrophic anaerobic bacteria to compete for traces of hydrogen depends on the redox potential of the terminal electron acceptor, Archives of Microbiology. 149 (4). pp. 350-357. 

Bibliography

Ralf, Cord-Ruwisch; H-J, Seitz; R, Conrad (1988), The capacity of hydrogenotrophic anaerobic bacteria to compete for traces of hydrogen depends on the redox potential of the terminal electron acceptor, Archives of Microbiology. 149 (4). pp. 350–357.

  1. ^ Sims, G.K. (2012). Ph.D. New York: Casteneda, S.F., Emerson, M.L., editors. Xenobiotics: New Research, Nova Science Publishers. pp. 67–84. 
  2. ^ Holliger, C.; Wohlfarth, G.; Diekert, G. (1998). "Reductive dechlorination in the energy metabolism of anaerobic bacteria". FEMS Microbiology Reviews 22 (5): 383.  

References

See also

Type Lifestyle Electron acceptor Products Eo' [V] Example organisms
aerobic respiration obligate aerobes and facultative anaerobes oxygen O2 H2O + CO2 + 0.82 aerobic prokaryotes
iron reduction facultative anaerobes and obligate anaerobes ferric iron Fe(III) Fe(II) + 0.75 Geobacter, Geothermobacter, Geopsychrobacter, Pelobacter carbinolicus, P. acetylenicus, P. venetianus, Desulfuromonadales, Desulfovibrio
manganese facultative anaerobes and obligate anaerobes Mn(IV) Mn(II) Desulfuromonadales, Desulfovibrio
cobalt reduction facultative anaerobes and obligate anaerobes Co(III) Co(II) Geobacter sulfurreducens
uranium reduction facultative anaerobes and obligate anaerobes U(VI) U(IV) Geobacter metallireducens, Shewanella putrefaciens, (Desulfovibrio)
nitrate reduction (denitrification) facultative anaerobes nitrate NO3 nitrite NO2 + 0.40 Paracoccus denitrificans, E. coli
fumarate respiration facultative anaerobes fumarate succinate + 0.03 Escherichia coli
sulfate respiration obligate anaerobes sulfate SO42− sulfide HS - 0.22 Desulfobacter latus, Desulfovibrio' oxygen
methanogenesis (carbonate reduction) methanogens carbon dioxide CO2 methane CH4 - 0.25 Methanothrix thermophila
sulfur respiration (sulfur reduction) facultative anaerobes and obligate anaerobes sulfur S0 sulfide HS - 0.27 Desulfuromonadales
acetogenesis (carbonate reduction) acetogens carbon dioxide CO2 acetate - 0.30 Acetobacterium woodii
dehalorespiration facultative anaerobes and obligate anaerobes halogenated organic compounds R-X Halide ions and dehalogenated compound X + R-H + 0.25–+ 0.60[2] Trichlorobacter (Geobacteraceae)

Examples of respiration

Specific types of anaerobic respiration are also used to convert toxic chemicals into less-harmful molecules. For example, toxic arsenate or selenate can be reduced to less toxic compounds by various bacteria.

Methanogenesis is a form of carbonate respiration that is exploited to produce methane gas by anaerobic digestion. Biogenic methane is used as a sustainable alternative to fossil fuels. On the negative side, uncontrolled methanogenesis in landfill sites releases large volumes of methane into the atmosphere, where it acts as a powerful greenhouse gas.

Dissimiltory denitrification is widely used in the removal of nitrate and nitrite from municipal wastewater. An excess of nitrate can lead to eutrophication of waterways into which treated water is released. Elevated nitrite levels in drinking water can lead to problems due to its toxicity. Denitrification converts both compounds into harmless nitrogen gas.

Economic relevance

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