How microalgae-bacteria consortia adapt sulfamethoxazole pressure: Insights from physiological and genetic responses

Microalgae-bacteria consortia (MBC) are regarded as an energy-saving alternative for wastewater treatment process, while their reliability is challenged under long-term antibiotic pressure. Unfortunately, the underlying physiological and genetic mechanisms enabling adaptation to such prolonged antibiotic pressure remain largely unknown. This study systematically investigates the adaptive responses of MBC systems to sulfamethoxazole (SMX) pressure during two exposure stages (100 and 200 μg/L). While the system remained stable at 100 μg/L SMX (stage I), its performance declined at 200 μg/L (stage II), with COD and ammonium removal decreasing by 7.5 % and 8.8 %, respectively. This was accompanied by adverse physiological responses, including a 36.3 ± 3.2 % decrease in photosynthetic oxygen production, a 96.2 ± 9.7 % increase in ROS levels, and a 49.0 ± 5.3 % reduction in EPS content. Remarkably, both pollutant removal and physiological state were fully restored following a 100-day recovery period. This resilience may be attributed to the enrichment of microbial communities such as Chlorophyta and Bacillariophyta, whose presence strongly correlated with reduced antibiotic resistance gene (ARG) dissemination. Genetic analysis further indicated that suppressed ATP synthase and electron transfer within the oxidative phosphorylation pathway may represent important adaptive costs. Fortunately, the response regulators within the two-component system functioned as central mediators, coordinating both extracellular EPS secretion and intracellular antioxidant activity. Overall, this study advances current understandings of adaptive mechanism and offers insights for facilitating stable operation under long-term antibiotic pressure.