Endogenous quorum sensing orchestrates microbial social behaviors for anaerobic digestion adaptation to temperature...

Anaerobic digestion (AD) offers a cost-effective and efficient approach for wastewater treatment, but the mesophilic anaerobic digestion only well performed within a narrow temperature range, typically between 30 and 40 °C. However, lower temperatures affected the performance of AD, microbial community and granular sludge properties. Recent studies mainly focused on adding exogenous quorum sensing (QS) signal molecules to accelerate the recovery of anaerobic digestion performance under pressure conditions, while few studies on endogenous QS molecules. To investigate microbial stress adaptation mediated by endogenous QS system under stepwise temperature reduction, an Upflow Anaerobic Sludge Blanket (UASB) reactor with gradual temperature reduction from 35 to 20 °C was constructed.

This study investigated the performance and microbial dynamics of the UASB reactor subjected to gradual temperature reduction from 35 to 20 °C. The reactor maintained stable COD removal efficiency (78-79%) even at 20 °C after adaptation. Temperature reduction shifted microbial community structure, with Proteobacteria becoming dominant at lower temperatures. Especially, Pleomorphomonas and the Christensenellaceae R-7 group are highly adaptable to low temperatures, and their flourish was the microbial basis of sustained performance of UASB under low-temperature stress. In archaeal community, the relative abundance of Methanosaeta belong to acetoclastic methanogen decreased, while the hydrogenotrophic methanogens Methanobacterium and Methanospirillum increased. These findings indicated that the methanogenic pathway transitioned from acetoclastic to hydrogenotrophic, likely contributing to sustained methanogenic activity. The results of Mantel test between QS molecules profiles, microbial community and granular sludge properties revealed the endogenously generated AHLs and AI-2 play a crucial role in optimizing the bacterial and methanogenic communities, resulting in faster recovery of the anaerobic sludge from temperature reduction.

Quorum sensing molecules, especially AHLs and AI-2, played a crucial role in regulating microbial social behaviors and EPS production under temperature stress. Moreover, These QS changes coincide with a shift from acetoclastic to hydrogenotrophic methanogenesis and with EPS composition adjustments (PN/PS changes), suggesting that QS promotes low-temperature adaptation by regulating EPS secretion and community adhesion, thereby stabilizing granule structure and maintaining metabolic syntrophy and methanogenesis. These findings enhance our understanding of temperature effects on anaerobic systems and provide a basis for optimizing psychrophilic anaerobic processes, addressing the need for energy-efficient wastewater treatment in colder climates.