Microbial and Functional Succession during Anaerobic Digestion along a Fine-Scale Temperature Gradient of 26–65 °C

Engineering robust or specialized microbial ecosystems by regulating the operating temperatures of anaerobic digestion (AD) has not yet received enough attention. Further, the critical temperature range for restructuring the structure and function of microbial community has not been assessed. In this study, batch AD experiments were conducted along a fine-scale 3 °C temperature gradient of 26–65 °C. Stable performance of AD was observed at 26–41 and 50–56 °C. However, sudden performance deterioration was observed at 47 and 59 °C, accompanied by a severe reconstruction of the microbial community and metagenomics-indicated functional dynamics. These effects were particularly observed during methanogenesis qualitatively and quantitatively, suggesting that 47 and 59 °C were the critical temperatures from mesophilic to thermophilic temperatures and from thermophilic to hyperthermophilic temperatures, respectively. Contrary to most prior studies, hydrogenotrophs also dominated at mesophilic temperatures, which suggested that the primary methanogenesis pathway shifted from acetoclastic and hydrogenotrophic to hydrogenotrophic, with the temperature shifting from mesophilic to thermophilic. The present study suggests that modulating operating temperatures to shape the microecosystem of the AD system is an efficient strategy, and avoiding a temperature pitfall at approximately 47 or 59 °C is imperative.