Long-term survival of methanogens of an anaerobic digestion sludge under starvation and temperature variation

To Investigate starvation effect on methanogen community, two Identical membrane reactors were continuously operated for 84 consecutive days, with a temperature change from 50°C to 20°C. Continuous feeding washed out 97% biomass from reactors during the experimental period. Quantitative PCR, using mcrA genes, indicated that the methanogen abundance decreased from 7.0×10⁷ to 1.2×10⁷ mcrA copies·ml^-1 (volume basis) at 50 °C, and then increased to 4.4 ×10⁷ mcrA coples-ml^-1 at 20 °C (p<0.05). Correspondence analysis Indicated that methanogen communities were distinctly grouped by each temperature. Canonical correspondence analysis Indicated that temperature showed a significant correlation with the methanogen community composition. These results suggest that methanogens can survive for a long time (at least more than 84 days) under starvation conditions, and that temperature could be a primary factor determining the density and community of methanogens.