Five SAR-302503 batch reactors were set up to investigate the correlations between Spirochaetes and hydrogenotrophic methanogens. Anaerobic sludge was collected from the five full-scale anaerobic digesters (S1, J2, N1, N2, and T1 digesters), located in Seoul, South Korea. The sludge samples were used as the inocula for the batch test examining methane production. Among them, the S1 and J2 digesters were operated under thermophilic conditions (48–51 °C), while the N1, N2, and T1 digesters were operated under mesophilic conditions (36–40 °C). Detailed information about the digesters and sludge, such as digester configuration, characteristics of feed waste, and operating conditions, were described in a previous study ( Lee et al., 2012). Before seeding the inocula into the batch reactors, all sludge samples were starved under anaerobic conditions for four days without the addition of feed at the same temperature conditions as the digesters from which the sludge samples were taken.