Bacterial N-acyl-homoserine lactone enhances the degradation of sulfamethoxazole by microalgae and the associated metabolic regulatory mechanisms

Recent studies have revealed that N -acyl-homoserine lactones (AHLs), common quorum-sensing (QS) signal molecules in Gram-negative bacteria, can also influence microalgal cells. However, their role in regulating the metabolism of pollutants, such as antibiotics, within microalgae remains poorly understood. This study investigated the effects of N -hexanoyl-L-homoserine lactone (C6-HSL) on the degradation of sulfamethoxazole (SMX) in aquaculture wastewater by Chlorella vulgaris . The addition of 0.5 μM C6-HSL resulted in the highest biomass accumulation and the maximum SMX removal efficiency (95.6 %). At optimal concentrations, C6-HSL effectively modulated key secondary messenger signaling pathways including reactive oxygen species (ROS), nitric oxide (NO), and calcium ions (Ca 2+ ) in microalgal cells. Additionally, it upregulated the activity of detoxification enzymes such as glutathione S-transferase (GST) and cytochrome P450 (CYP450), thereby altering SMX degradation pathways and significantly enhancing its removal. Transcriptomic analysis further demonstrated that exogenous C6-HSL upregulated critical genes associated with ROS, Ca 2+ , and NO signaling, along with genes encoding antioxidant enzymes and those involved in SMX metabolism. These findings indicated that C6-HSL, as a bacterial QS signal, could enhance microalgal tolerance and antibiotic degradation, offering a novel strategy to improve microalgae-based antibiotic removal in wastewater treatment.