Functionalization of Methane in Anaerobic Microorganisms

摘要

Aipproximately 140 Gt (1 Gt = 10~(15) g) of biomass (70 Gt carbon) are formed globally each year from CO2 via oxygenic photosynthesis (net primary production). Of this amount, 2-3 % end up in anaerobic environments that not only lack O2 but are also deficient in other electron acceptors with a high redox potential, such as nitrate, manganese(IV), iron(III), and sulfate. Such environments include freshwater sediments, swamps, paddy fields, landfills, the intestinal tract of ruminants and termites, and deeper layers of marine sediments. In these methanogenic environments, the biomass is fermented to methane, which involves anaerobic bacteria, protozoa and/or fungi, and methanogenic archaea, yielding approximately 1 Gt CH4 per year. Recalcitrant biomass components, such as lignin, require up to thousands of years to be completely fermented. Methane is also formed from biomass thermogenically and from carbonate geochemically. Methane has built up to large deposits over millions of years; the quantities trapped in methane hydrates alone are estimated to be up to 10000 Gt (Figure 1).