Emerging contaminant stress promotes greenhouse gas production through microbial defence–energy trade-off in receiving rivers

Abstract

Rivers receiving wastewater treatment plant effluents accumulate emerging contaminants (ECs) and generate greenhouse gases (GHGs), yet how EC mixtures reshape microbial metabolism remains unclear. Here we investigated a wastewater treatment plant–receiving river continuum by integrating 159 ECs, cytotoxicity, GHGs, risk prioritization, multi-omics and controlled microcosms. Although treatment removed 82.21% of ECs, effluent increased downstream ECs (53.21%), cytotoxicity (44.15%) and CO2 equivalents (11.31%). Moreover, defence functions (efflux pumps, biofilm formation and P450 detoxification) declined by 52.34–57.98%, whereas GHG-linked carbon/nitrogen genes were 1.94–33.67 times more abundant than upstream levels, beyond what could be explained by source mixing alone. Semi-continuous microcosms comparing EC-rich effluent, upstream and EC-depleted effluent showed that EC stress suppressed defence functions while activating respiration, fermentation and carbon/nitrogen transformations. Enzyme and metabolite analyses revealed EC-induced oxidative stress and transient energy depletion, followed by recovery of acetyl-CoA content, citrate synthase activity and adenosine triphosphate availability, indicating a shift from defence to energy maintenance, thereby promoting GHG generation under long-term downstream EC exposure. Using multi-omics and microcosm analyses, this study shows that mixtures of emerging contaminants suppress microbial defence functions while redirecting metabolism towards energy production, enhancing greenhouse gas generation.