Anaerobic digestion is the method of wastes treatment aimed at a reduction of their hazardous effects on the biosphere. The
mutualistic behavior of various anaerobic microorganisms results in the decomposition of complex organic substances into simple,
chemically stabilized compounds, mainly methane and CO2. The conversions of complex organic compounds to CH4 and CO2
are possible due to the cooperation of four different groups of microorganisms, that is, fermentative, syntrophic, acetogenic, and
methanogenic bacteria. Microbes adopt various pathways to evade from the unfavorable conditions in the anaerobic digester
like competition between sulfate reducing bacteria (SRB) and methane forming bacteria for the same substrate. Methanosarcina
are able to use both acetoclastic and hydrogenotrophic pathways for methane production. This review highlights the cellulosic
microorganisms, structure of cellulose, inoculum to substrate ratio, and source of inoculum and its effect on methanogenesis.
The molecular techniques such as DGGE (denaturing gradient gel electrophoresis) utilized for dynamic changes in microbial
communities and FISH(fluorescent in situ hybridization) that deal with taxonomy and interaction and distribution of tropic groups
used are also discussed.