Methane bacterial activities

Below the stage of methane production is the fermentation (fifth) stage, followed by the sixth, thermocatalytic stage at still greater depths. The initial five stages require the presence of bacteria below stage five, bacterial activity ceases... 

Carbon monoxide (CO), a toxic gas, is produced during combustion, both in wildfires and in fuel-burning devices CO also can be produced and consumed by bacterial activity. The presence of CO may indirectly increase the atmospheric mixing ratios of other gases by competing for oxidant species (such as the hydroxyl radical, OH-), thereby decreasing the oxidation rates of the other gases. This competition for oxidant species is believed to be one reason for the current increase in atmospheric methane, whose major atmospheric sink is reaction with the hydroxyl radical. 

A process of bacterial degradation of carbon compounds can be conceived essentially as a conversion from a C02-predominant to a CH4-predominant system (Stumm and Morgan, 1981). The production of organic methane by microbial activity is a typical example of such conversion. Organic matter is first transformed into organic acids, which are then decomposed into acetic acid, gaseous hydrogen, and CO2, and finally recombined as CH4 ... 

To summarize, the isotopic and textural evidence collectively implies the activity in the Belingwe belt of a variety of prokaryotic processes (1) sulphate reduction and possibly photosynthetic sulphide oxidation (2) operation of rubisco both in cyanobacterial stromatolites (as expected) but also possibly in non-photosynthetic sulphur-bacterial mats (3) oxygenic photosynthesis (in stromatolites) (4) methanogenesis and methane oxidation. Most probably, other sulphur-based metabolic reactions (e.g. dissim-ilatory sulphate reduction) were also taking place. This complexity is consistent with the relative timing of the metabolic phylogeny deduced from rRNA studies (Woese 1987 Pace 1997). 

We consider briefly the structure and mechanism of action of soluble MMO (sMMO), the best characterized of the BMMs (bacterial methane monooxygenases) (Figure 13.27), which is able to activate the inert C—H bond of... 

Hydrothermal and mantle contributions of methane are not significant. Oceanic surface waters are oversaturated with respect to methane, due to bacterial (methanogenic) activity in localized anaerobic environments, such as the digestive tracts of zooplankton, resulting in a net flux of methane to the air. Methane is similarly produced in freshwater environments. Deep ocean waters contain much lower methane concentrations than surface waters and the methane generated within anaerobic sediments is mostly oxidized by methanotrophes. Marine and lacustrine environments as a whole do not make a large contribution to the methane flux, but natural wetlands do. The bacterial... 

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