Exogenous AHLs can effectively promote propionic acid oxidation and methanogenesis by regulating syntrophic consortia

Environmental context Anaerobic digestion (AD) is an important wastewater treatment technology. Quorum sensing (bacterial communication) regulates the interaction relationship between microorganisms, but the regulatory mechanism for methanogenic microorganisms in AD remains unclear. This study found that certain microbially produced chemicals (N-acyl homoserine lactones) can effectively regulate metabolic processes, encouraging mutualism and symbiosis between syntrophic bacteria and methanogens, making AD more efficient. Rationale This paper adopts an effective regulatory method for group social behaviour – quorum sensing – to achieve the regulation of syntrophic bacteria metabolism and increase methane production. The key focus is on the process in which the electronic carriers synthesised by the metabolism of syntrophic bacteria are used by methanogens. The results of this study will provide an effective regulatory means for enhancing the methanogenic efficiency during anaerobic digestion. Methodology A co-culture system of propionic acid co-oxidising bacteria and methanogens was constructed through anaerobic granular sludge acclimation. Different types of N-acyl homoserine lactones (AHLs, 2.0 µg L–1) were added, including C4-HSL, C6-HSL, C8-HSL, C10-HSL and C12-HSL. The degradation rate of propionic acid, methane production, enzyme activity and microbial community structure were investigated. Results It was found that C4-HSL, C6-HSL and C12-HSL entered the rapid degradation period 1 day earlier than the blank group; methane production was enhanced by 28.3, 23.4 and 26.4% respectively; and the activities of formate dehydrogenase (FDH) enzymes were increased by 107.8, 86.2 and 90.0% respectively; and H2ase activity increased by 71.3, 90.1 and 69.1% respectively. Discussion Gene prediction indicated that AHLs promoted the process by regulating the FDH and H2ase genes. The AHLs enhanced the methanogenic process by enhancing enzyme activity. This was an important discovery that AHLs regulated the methanogenic production of methanogens’ metabolism, and it provided a new strategy for the regulation of anaerobic digestion (AD).