Methanogenesis electron acceptors

The sequence of electron-acceptor utilization can be spatially observed in horizontal layers of increasing depth in aquatic water columns and sediments. In a typical littoral marine sediment, only the first few millimeters of the sediment are oxygenated and nitrate serves as the electron acceptor. Below this, for several meters, sulfate is the principal electron acceptor. Methanogenesis is usually confined to the sulfate-depleted deeper sediment layers methane... 

In the final step of methanogenesis, methyl coenzyme M reductase catalyzes the reaction of methyl coenzyme M (CH3 S-CoM) with coenzyme B (CoB-SH) to form methane and the CoM-S-S oB heterodisulfide. The heterodisulfide functions as the terminal electron acceptor of... 

A second site for ATP synthesis in acetate fermentation appears be the oxidation of the enzyme-bound CO to CO2. This was deduced from the following findings cell suspensions of Methanosarcina barkeri catalyze the oxidation of free CO to CO2 with as electron acceptor, when methanogenesis is inhibited by bromoethanesulfonate [233] ... 

A wide variety of evidence suggests that carbon availability limits methanogenesis in situ. The fact that methanogenesis is often inhibited by the presence of alternative electron acceptors such as Fe(lll) and SO is evidence of competition for fermentation products and thus widespread carbon limitation of the process (Section 8.08.8). 

A more recent addition to the list of terminal electron acceptors is humic substances (Section 8.08.6.4.1). Cervantes et al. (2000) demonstrated that a humic acid analogue (AQDS) inhibited methanogenesis due to a combination of toxic and... 

Frenzel P., Bosse U., and Janssen P. H. (1999) Rice roots and methanogenesis in a paddy soil ferric iron as an alternative electron acceptor in the rooted soil. Soil Biol. Biochem. 31, 421-430. 

Internal Sources and Atmospheric Exchange of Methane. Methane is produced by specialized groups of obligate anaerobic bacteria (22, 23). The formation of methane as a metabolic product results either from the microbial reduction of CO2 with molecular H2, or via the fermentation of acetic acid. More structurally complex substrates may also serve as electron acceptors/donors, but the end result of methanogenesis is to produce methane and CO2 as end products (23). 

Within the first 20 m, all dissolved and solid oxidants are depleted (Figure 11,6b,c). Microbial metabolism uses DOC and electron acceptors in the sequence 02, NO(T, SO -, then methanogenesis becomes the dominant pathway for biodegradation. When... 

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