Inhibiting Cr(VI)-mediated ARG dissemination in wastewater: Synthetic antioxidant-, extracellular polymeric...

Heavy metals (HMs) trigger the sustained enrichment and dissemination of antibiotic resistance genes (ARGs) by exerting selective pressure, and there is an urgent need for effective and environmentally friendly control strategies. Herein, we found that long-term (180 d) hexavalent chromium [Cr(VI)] stress (10 mg/L) could facilitate the enrichment of multidrug-resistant plasmids (e.g., bla_TEM and sul1) and significantly increase (p < 0.05) the conjugative transfer frequency. Subsequently, we constructed a synthetic carotenoid- and extracellular nuclease gene exeM-producing microbiome centered on Deinococcus radiodurans R1, which synthesizes and secretes extracellular polymeric substances (EPS) via the Wzx/Wzy-dependent pathway, thereby alleviating environmental oxidative stress by adsorbing Cr(VI) (over 85%) and scavenging ROS (approximately 18-26-fold). qPCR results demonstrated that the synthetic microbiome effectively reduced ARG abundances, along with the mobile genetic elements traG and intI1 (by more than one order of magnitude, MGEs) and the metal resistance gene chrA (by more than two orders of magnitude, MRG). Electron microscopy and metagenomic analysis demonstrated that the synthetic microbiome could further reduce the co-occurrence of ARGs and MRGs (e.g., tetA, chrA, and chrB) by impairing plasmid integrity and preserving cell membrane integrity (ompC, oprC, plsB, and fabR), thus inhibiting horizontal gene transfer. In addition, it reduced the abundance of Pseudomonadota (the host harboring ARGs and MGEs, p < 0.05) by 33-48%. This study provides a sustainable bioremediation strategy for controlling the dissemination of ARGs in heavy metal-polluted wastewater.