Bacteria autotrophic methanogens

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). ... 

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... 

Hydrogen produced by some anaerobic bacteria can be utilized by autotrophic bacteria to reduce oxidized organic compounds and COz to form either acetic acid (acetogenic bacteria) or methane (methanogenic bacteria), as follows ... 

Calvin cycle (see), and a lesser amount by the Hatch-Slack-Kortschack cycle (see). C. can also be driven by chemical energy in autotrophic or che-moautotrophic organisms, in particular bacteria. Some of these use a process similar to the Calvin cycle. The methanogenic bacterium, Methanobacterium thermoautotrophicum, however, fbtes CO2 by a series of S major reactions which do not include the Calvin cycle (Fig.). There is also anaplerotic CO2 fixation (see Carboxylation, Biotin enzymes). 

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