Hydrogen cycle

For the nuclear fusion process producing helium from hydrogen see Proton-proton chain reaction

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Hydrogen is one of the constituents of water. It recycles as in other biogeochemical cycles. It is actively involved with the other cycles like the carbon cycle, nitrogen cycle and sulfur cycle as well.

Anaerobic fermentation of organic substances to carbon dioxide and methane is a collaborative effort involving many different biochemical reactions, processes and species of microorganisms. One of these many processes that occur is termed "interspecies hydrogen transfer". This process has been described as integral to the symbiosis between certain methane-producing bacteria (methanogens) and nonmethanogenic anaerobes. In this symbiosis, the nonmethanogenic anaerobes degrade the organic substance and produce -among other things- molecular hydrogen (H₂). This hydrogen is then taken up by methanogens and converted to methane via methanogenesis. One important characteristic of interspecies hydrogen transfer is that the H₂ concentration in the microbial environment is very low. Maintaining a low hydrogen concentration is important because the anaerobic fermentative process become increasingly thermodynamically unfavorable as the partial pressure of hydrogen increases.

References

Bibliography

• "Microbiology and Biochemistry of Strict Anaerobes Involved in Interspecies Hydrogen Transfer" by Jean-Pierre Bélaich; Mireille Bruschi; Jean-Louis Garcia; Federation of European Microbiological Societies. Published Nov 1990. ISBN 0306435179

• [1] F.A.M. de Bok, C.M. Plugge, and A.J.M. Stams; "Interspecies eletron transfer in methanogenic proprionate degrading consortia". Water Research 38 (2004): 1368-1375

• [2] A.J.M. Stams et al., "Exocellular electron transfer in anaerobic microbial communities", Environmental Microbiology, 8 (2006):371-382