Unveiling the role of aeration tanks in the emission and enrichment of airborne antibiotic resistance genes in a wastewater treatment plant

The aeration tanks in wastewater treatment plants (WWTPs) are important sources of airborne antibiotic resistance genes (ARGs) and antibiotic-resistant bacteria (ARB) due to bubble bursts at the air-liquid interface. This study employed an integrated metagenomic workflow, encompassing reference-based, assembly-based, and binning-based modules, to investigate resistomes in a WWTP in northern Taiwan. The role of aeration tanks in emitting airborne ARGs and their associated risks was assessed. The findings revealed a strong similarity between the ARG profiles in aeration tank wastewater and surrounding PM2.5, indicating atmospheric transmission of ARGs. Notably, the ARG level in PM2.5 (0.83 +/- 0.11 ARGs/cell) was 59.6 % higher than in wastewater (0.52 +/- 0.01 ARGs/cell). The assembly-based analysis showed that foam-forming bacteria such as Mycobacterium and Gordonia dominated ARGs-carrying contigs in PM2.5, suggesting that higher atomization capabilities of ARB contribute to airborne ARG prevalence. Furthermore, a significant proportion of stress response genes and increasing efflux pump resistance (122.6 %) in PM2.5 imply that mechanical forces during aerosolization and harsh atmospheric conditions select for airborne ARB capable of overcoming stress induced by dramatic environmental changes. Overall, the study indicates that ARG risk is intensified in PM2.5 due to their abundance, mobility, and pathogenicity. In conclusion, aeration tanks not only emit airborne ARGs but also cause an unexpected enrichment effect and exposure risk during aeration, highlighting the critical water-to-air transmission route of ARGs in WWTPs.