초록
<P><B>Abstract</B></P> <P>To understand the syntrophic mechanism of acetogens and methanogens in anaerobic digestion (AD), functional floras of syntrophic propionate-oxidizing bacteria (SPOB), syntrophic butyrate-oxidizing bacteria (SBOB), aceticlastic methanogens (AM) and hydrogenotrophic methanogens (HM) were separately tested by microbial density to reveal their performance in metabolic activity, extracellular polymeric substances (EPS) production and quorum sensing (QS) signal molecules (acyl homoserine lactones, AHLs) secretion, as well as the regulation of endogenous AHLs in balancing the social behaviors of syntrophic microorganism. The results showed that methanogenesis, EPS production and AHLs secretion of the functional floras were all observably affected by microbial density. The metabolic activity of SBOB, SPOB, AM and HM decreased with a microbial density more than 344, 295, 229 and 237 mgMLVSS/L, respectively. The intraspecific regulation of SPOB and HM were achieved with the mediation of OXOC6-HSL and C10-HSL, respectively. With the mediation of enjoyed signal molecules, metabolic coordination between SPOB and AM was of bidirectional regulation, but it was a unidirectional regulation from HM to SPOB. Syntrophic acetogens and methanogens in AD could bidirectionally regulate their EPS production via QS system to construct syntrophic floras that make the methane fermentation of propionate and butyrate more efficient. The present research work provides a practical strategy to regulate endogenous AHLs by microbial density to enhance the syntrophism of acetogens and methanogens in AD.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Effect of microbial density on syntrophic acetogens and methanogens was revealed. </LI> <LI> AHLs secretion of acetogens and methanogens were affected by microbial density. </LI> <LI> Social behavior of syntrophic acetogens and methanogens was mediated by the AHLs. </LI> <LI> Mediation of endogenous AHLs between acetogens and methanogens was networked. </LI> <LI> Microbial density control was a feasible approach to regulate endogenous AHLs in AD. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>