Autotrophic methanogens

Winter J, C Lerp, H-P Zabel, F X Wildenaner, H Konig, F Schindler (1984) Methanobacterium wolfei, sp. nov., a new tungsten-requiring, thermophilic, autotrophic methanogen. Syst Appl Microbiol 5 457-466. 

Heterotrophic methanogens use acetate directly for biosynthesis and as an energy source. During this process, methanogens convert acetate to carbon dioxide and methane by utilizing a different biochemical pathway than the autotrophic methanogens. The sequence of reactions involved are as... 

H4SPt is the tetrahydrosarcinapterin cofactor. The a2S2 units correspond to CODH, /3 is ACS, yS is a corrinoid cobalt-containing iron-sulfur protein (CoFeSP) that transfers a methyl group to H4SPt. The electron acceptor is a ferredoxin (see [36] and references therein). A similar complex is used by obligate chemo-autotrophic methanogens, such as Methanococcus jannaschii, to catalyze the formation of acetyl-CoA from CO2 and H2 in the reverse reaction [35]. 

The catalysis of the transfer of a methyl group is an important role of enzyme-bound vitamin B12 derivatives in human, animal, and bacterial metabolism. The known enzyme-controlled methyl group-transfer reactions are key steps in the cobamide-dependent methylations of homocysteine to methionine, in the metabolic formation of methane from other Ci-compounds in methanogenic bacteria, and in the fixation of carbon dioxide via the acetyl coenzyme A pathway of some bacterial autotrophs (Figure 10). ... 

Methanogens appear to interconvert glucose and pyruvate via the normal glycolytic pathway shown in Fig. 1. However, most methanogens are autotrophs and carbon is fixed into acetyl-CoA thus, much of the evidence for an Embden-Meyerhof route has been gained in the direction of carbohydrate synthesis and then mainly from the one organism, Methanobacterium thermoautotrophicum. 

Almost all methanogen species can grow on H2+CO2 carrying out autotrophic cell carbon biosynthesis [183]. Due to simplicity of the catabolites, C02-reduction to methane has been extensively used as a model system to study the biochemistry of methanogenesis. Most of this work has used M. thermoautotrophicum, and to a lesser extent, M. barkeri. 

Hydrogen Oxidation Kinetics. Shea et al. (22) studied the kinetics of methane fermentation by an enrichment culture of lithotrophic (autotrophic) hydrogen oxidizing methanogenic bacteria at 37 °C. Reported values of the kinetic coeflScients are as follows (1) Y = 0.043 mg volatile suspended solids per mg of hydrogen COD removed, (2) b = —0.009 day"S (3) k = 24.8 mg hydrogen COD removed per mg volatile suspended solids per day and (4) Ks = 569 mm of mercury, hydrogen pressure. 

Bhatnagar L, Jain MK, Zeikus JG (1991) Methanogenic bacteria. In Shively JM, Barton LL (eds) Variations in autotrophic life. Academic Press, London, pp 251-270 Blake RC Jr, Howard GT, McGinness S (1994) Enhanced yields of iron-oxidizing bacteria by in situ electrochemical reduction of soluble iron in the growth medium. Appl Environ Microbiol 60 2704-2710... 

Table 5.8 Isotopic composition of major autotrophes and methanogens (data after Schidlowski 1988)...

---