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Highlights • Specific QS signals of various populations in anaerobic digestion were identified. • Most AHLs in anaerobic digestion were secreted in starvation conditions. • The specific QS signals induced the K -strategy of populations to survive. • The QS regulated cooperation among populations in resource-limited situations. • Profiles of AHLs indicated the performance of anaerobic digestion processes. Abstract A series of dominant functional floras involved in anaerobic digestion was obtained by subculturing anaerobic sludge with specific substrates, respectively, and their specific quorum sensing signals (AHLs) were identified. It was found that most of the AHLs were secreted in starvation of the functional floras. One or two AHLs were found to have a significant positive correlation with the behavior of hydrolytic-fermentative bacteria, homoacetogens, syntrophic propionate-oxidizing bacteria, syntrophic butyrate-oxidizing bacteria and aceticlastic methanogens, respectively. Hydrogenotrophic methanogens had a various self-organization means and broader relations with the other populations, which was induced by six AHLs at least. Performance of an upflow anaerobic sludge blanket in the startup process revealed that the dominant populations involved in anaerobic digestion would secret specific AHLs to induce K -strategy in resource-limited situation for reproduction and regulating their cooperation. This work presents a novel perspective on the social behaviors of microbial populations in anaerobic digestion. [ABSTRACT FROM AUTHOR]

Bicarbonate (HCO 3 − ) has been extensively researched as a buffer in anaerobic digestion. The effect of HCO 3 − concentration on syntrophic butyrate oxidation process was evaluated by batch culturing of anaerobic activated sludge, and the mechanism was further revealed by the changes of Gibbs free energy (Δ G ) and the interspecies transfers of electron and proton. The results showed that butyrate degradation rate was enhanced by 32.07% when the supplement of HCO 3 − increased from 0 to 0.20 mol/L. However, methane production and acetate degradation were strongly inhibited by HCO 3 − more than 0.10 mol/L. More function of HCO 3 − was found as 1) decreasing the Δ G of syntrophic methanogenesis of butyrate while increasing the Δ G of methanogenesis of acetate, 2) enriching M. harundinacea and M. concilii , 3) increasing the diffusion rate of protons between the syntrophic consortia. This work would increase the anaerobic digestion efficiency by enhancing the interaction of the syntrophic consortia. [ABSTRACT FROM AUTHOR]