The Population Features of Methanogens and the Biodegradation of Hydrocarbons in Coal Organic Matters

methane and have wide distribution in lakes, swamps, paddy fields and ruminant rumen in the earth surface ecosystem. As a very important greenhouse gas, methane of different sources can induce global warming (Table 1). Hence, more and more attentions are paid to the population features of methanogens and formation mechanisms of biogenic methane. However, microbial coalbed methane (CBM) has good resource prospect and exploitation potential because of the large distribution, shallow buried depth and low exploration and development cost. In the newest taxonomy system, there are four classes (Methanobacteria, Methanococci, Methanomicrobia and Methanopyri), seven orders, fourteen families and thirtyfive genera for methanogens (Wang et al., 2014). Moreover, most of the researches were mainly focused on Methanomicrobia, which has four orders, nine families and twenty-five genera. The genome size for methanogens is usually between 1.6×10~5.7×10 bp, and the genome is made up by a circular chromosome. During the formation of microbial methane, different enzymes in bacteria such as MFR, THMP, HSoCM, CoF420, CoF430 and HS-HTP play significant roles. By monitoring the variation characteristics of special enzymes during the methanogenesis can help to understand the metabolic rule of methanogens. For example, under ultraviolet excitation conditions, CoF420 may generate blue-green fluorescence. Based on the substrate types for methanogens metabolism, the microbial methane can be generated by three paths: (1) Acetic fermentation; (2) H2/CO2 reduction; (3) Methyl/methanol-utilization. The amount of biogenic methane generated by acetic fermentation is up to 67% in nature, H2/CO2 reduction and methyl/methanol utilization formed the other 33%. Acetic fermentation: CH3COOH→CH4 +CO2 H2/CO2 reduction: CO2+8H+8e⎯→CH4+2H2O Methyl/methanol-utilization: CH3-A+H2O→CH4+CO2+A-H