Deciphering the code of temperature rise on aerobic granular sludge stability: A DSF-c-di-GMP mediated regulatory mechanism

Diffusible signal factor (DSF)-c-di-GMP-mediated strategies have been proposed as an effective regulatory approach for signal molecules in aerobic granular sludge (AGS). The increase in temperature from low to normal levels had a significant impact on AGS stability. In this study, two reactors were established to investigate the effects of different temperature rise modes (abrupt or gradual) on AGS stability. Following the temperature rise, the DSF concentration in Reactor 1 (R1, abrupt) rose nearly fourfold by day 125, while LB-EPS levels decreased by 70%. In contrast, in Reactor 2 (R2, gradual), the DSF concentration increased by only twofold, and TB-EPS levels decreased by 25%. Flavobacterium (R1: 3.64%→0.41%, R2: 3.70%→1.97%) and Thauera (R1: 28.62%→4.01%, R2: 27.56%→13.10%), which are associated with EPS and signal molecule production, exhibited significantly different trends in response to the different temperature rise modes. Batch experiments exhibited that the exogenous addition of DSF and the DSF inhibitor, salicylic acid (SA), can regulate EPS content by altering the concentration of signaling molecules, particularly the LB-EPS, thereby reducing the risk of sludge collapse. These findings offer novel insights into the role of DSF in bacterial communication during AGS formation under temperature rise, providing a basis for regulating AGS formation and stability.