Coexposure to Environmentally Relevant Concentrations of Sulfamethoxazole and Graphene Oxide Boosted Aerobic Denitrification by Pseudomonas psychrophila HA-2

Antibiotics and engineered nanomaterials are widely recognized as emerging contaminants in the aquatic environment. While the individual toxic effects of sulfamethoxazole (SMX) and graphene oxide (GO) on denitrifying microorganisms have been well-documented, their combined effects under environmentally relevant concentrations remain poorly understood. This study investigated the joint influence of SMX and GO on aerobic denitrification by the newly isolated strain Pseudomonas psychrophila HA-2. The results showed that while single exposure to either contaminant induced inhibitions of nitrate removal, coexposure to environmental concentrations of SMX and GO unexpectedly enhanced aerobic nitrate reduction efficiency, with this stimulatory effect remaining stable over long-term cultivation. Mechanistically, the transcriptomic repression of apoptotic and necroptotic signaling, coupled with physiologically elevated electron transport activity, switched cells from a passive suppressed state to an active adaptive mode that prioritized energy replenishment and stress resistance over programmed cell death. Active defense involving enhanced extracellular polymeric substance (EPS) production and SMX efflux and a metabolic promotion cascade involving upregulated electron transport activity and energy synthesis drove coordinated adaptation and improved denitrification performance. SMX and GO exhibited synergistic effects on the induction of microbial hormesis, particularly by collectively boosting the energy synthesis. Overall, the findings refine our understanding of microbial responses to combined emerging anthropogenic pollutant stress, offering mechanistic insights into how aerobic denitrifying bacteria cope with co-occurring antibiotic and nanomaterial pollutants.