Fermentation system of biogas production is a complicated ecology system, and more than 99% of the microorganisms in biogas digesters are unculturable. To optimize conditions for cellulose conversion and biogas production in biogas digesters, and also to investigate the microbial diversity in biogas digesters, Chemical lysis method, lysozyme lysis method and QIAamp DNA Stool Mini Kit were used to extract total microbe DNA of biogas digesters, and then the DNA quality, the DNA yield, the size of DNA fragments, and existence of PCR inhibitor were examined, finally PCR-DGGE profiles were carried ...