Methanogenesis, archaea

These reductases play a key role both in methanogenesis and in the degradation of phenols that carry several nitro groups, which is discussed further in Chapter 9, Part 5. Although these reductases are typically found in methanogens, they have been encountered in a number of other bacteria and archaea ... 

Methanogenesis H2 C02 OO2, possibly formate, acetate 4H2+ CO2 CH4 + 2H2O (CO2 reduction) CH3COOH CH4 + CO2 (acetate fermentation) Mesophilic to hyperthermophilic archaea at vents and seeps... 

In contrast to Sec-tRNA and fMet-tRNA formation, Pyl-tRNA y formation can occur by direct acylation of pyrrolysine onto tRNA i Pyrrolysine (Pyl), the twenty-second amino acid, was discovered incorporated in methylamine methyltrans-ferases from Methanosarcinaceae, a branch of methanogenic archaea that has the ability to reduce a wide variety of compounds to methane including carbon dioxide, acetate, methanol, methylated thiols, and methylated amines (72). Methanogenesis... 

Lehmann-Richter, S., GrosBkopf, R., Liesack, W., Frenzel, P., and Conrad, R. (1999). Methanogenic archaea and CO2-dependent methanogenesis on washed rice roots. Environ. Microbiol. 1, 159-166. 

Janssen, P.H. and P. Frenzel. 1997. Inhibition of methanogenesis by methyl fluoride studies of pure and defined mixed cultures of anaerobic bacteria and archaea. Appl. Environ. Microbiol. 63 4552-4557. 

It is not known if all archaea contain adenylated corrinoids or not, however, because most archaea contain a corrinoid adenosyl transferase (CobA) orthologue it is presumed that the corrin biosynthetic intermediates are adenylated. The archaeal ATP Co(I)rrinoid adenosyltransferase from M. mazei strain Gol has been cloned and characterized. Unlike the bacterial enzyme, the M. mazei CobA was found to prefer cobalamin as a substrate over cobinamide, have increased selectivity for ATP over other nucleotides, and was able to utilize 2-deoxynucleotides (dCTP) as well as ribonucleotides. " As it is the methylated form of cobalamin, not the adenylated form, that is involved in methanogenesis, a possible role of the adenylated form of the coenzyme has not been determined. 

As indicated in Figure 4.6, the last step in the sedimentary metabolic pathway is methanogenesis. The formation of methane at a depth level, where all sulfate has been consumed, involves a group of strictly anaerobic archaea, collectively called methanogens. They use a small number of different low-molecular-weight substances for the biosynthesis of methane which, together with elemental hydrogen, in turn are formed... 

Below the sulfate zone, methanogenesis is the main terminal pathway of organic carbon mineralization. Methane is produced exelusively by anaerobic archaea that utilize a narrow speetrum of substrates for the process (Whitman et al. 

Acetotrophic archaea (genera Methanosarcina, Methanosaeta, Methanothrix) have the capability for such methanogenesis. It is believed that this process is responsible for the generation of most, up to 70%, of methane in the subsurface. 

Hydrogenotrophic methanogenesis are archaea, which, using H as electron donor, are reducing carbon of CO, HCOj or formiat HCOO and forming CH ... 

Acetidastic methanogenesis are also archaea, for which major substrate is either only acetate at its low concentrations (Methanosaeta sp) or both acetate and methanol and other compounds with one carbon atom, and also mix of Fi and CO at high acetate concentrations (Methanosardna sp.) (Westerholm, 2012). The process of acetidastic methanogenesis itself is viewed as decomposition of acetate into methyl (CH ) and carboxylic (COOH) groups. The former converts into CH, the latter is oxidized to CO. ... 

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