Decoupling antibiotic degradation from resistance development: photogranules act as a biocontainment for ARGs in wastewater

Bacterial granular sludge (BGS) efficiently removes antibiotics but acts as a hotspot for the enrichment of antibiotic resistance genes (ARGs). To decouple removal from resistance, we integrated Microcystis aeruginosa with BGS to form a cyanobacterial–bacterial granular sludge (CBGS) system. During 120-day operation under multi-class antibiotic stress (0–500 µg L⁻¹), CBGS demonstrated enhanced structural stability, pollutant removal, and a higher antibiotic elimination capacity (93.71–671.93 vs. 93.38–499.63 µg L⁻¹ d⁻¹ in BGS). Simultaneously, the system achieved suppression of endogenous microcystin-LR (a cyanotoxin variant containing Leucine and Arginine) release. Metagenomic, network, and transformation product analyses revealed that cyanobacterial integration induced a functional decoupling within the community, promoting oxidative biodegradation pathways and reducing selective pressure on ARG hosts. Mobility gene analysis further indicated restricted horizontal gene transfer, limiting ARG exchange between biomass and effluent. Consequently, ARG abundance decreased in effluents for 13 of 20 types in CBGS but increased for 16 of 20 in BGS. This study deepens our understanding of how microbial consortia can be engineered to separate antibiotic degradation from resistance propagation, offering a promising biologically contained strategy to mitigate resistance risks in wastewater treatment.