Quorum sensing molecules promote the nutrients removal in a HN-AD bacteria-Chlorella symbiotic system

The symbiotic system of heterotrophic nitrification-aerobic denitrification (HN-AD) bacteria and Chlorella shows significant nitrogen and phosphorus removal in biogas slurry treatment. It uses quorum sensing signaling molecules to form symbiotic biofilms, significantly boosting nitrogen and phosphorus removal efficiency. This study systematically explored the effect of exogenous N-octanoyl-DL-homoserine lactone (C8-HSL) concentrations on pollutant removal efficiency, extracellular polymeric substance (EPS) production, and microbial dynamics in the HN-AD bacteria- Chlorella symbiotic system. Results showed that the pollutant removal of the symbiotic system is maximized when the C8-HSL concentration is 0.8 μM. At concentrations below 0.8 μM, the system significantly enhances pollutant removal through increased EPS secretion. However, when the concentration exceeds 0.8 μM, both EPS production and pollutant removal are inhibited. Metagenomic analysis shows that C8-HSL at 0.8 μM can enrich key bacterial genera such as Halomonas and Sphingobium . By regulating key genes like narGHI , nirKS , phnX , and ppa , it adjusts their metabolic pathways, thereby influencing nitrogen and phosphorus removal. This highlights the crucial role of C8-HSL concentration in pollutant removal within HN-AD- Chlorella symbiotic systems.