Cyanobacteria-mediated attenuation of antibiotic resistance genes during long-term photocatalytic-biological treatment of sulfamethoxazole

ICPB induced early ARGs enrichment but unexpectedly later inhibition. • Cyanobacteria proliferation under continuous light mitigated ARGs dissemination. • Algal carotenoid biosynthesis pathway was activated to scavenge oxidative stress. • Cyanobacterial photosynthesis shifted microbial metabolism toward autotrophy. • Energy-extensive ARGs like efflux pump transporters were notably downregulated. The intimate coupling of photocatalysis and biodegradation (ICPB) serves as a promising alternative for rapid, enhanced antibiotics removal, while the concurrent induction of antibiotic resistance genes (ARGs) accumulation has become a critical barrier restricting its further industrial popularization. Here, we tracked ARGs fates in an ICPB reactor treating sulfamethoxazole (SMX) over 30 days, with emphasis on how microbial succession and functional adaptation within algae-bacteria consortia shape ARG dynamics. The ICPB system removed more than 71.7% of SMX within the first 7 days, yet this early-stage performance coincided with increased abundance of sul genes and the overall resistome, likely driven by folate biosynthesis and oxidative stress responses. With prolonged operation to 30 days, total ARGs abundance declined unexpectedly, even though SMX residuals accumulated. This shift was closely associated with sustained illumination that promoted algal proliferation, particularly Cyanobacteria. In parallel, carotenoid production was markedly enhanced through activation of the ε-carotene biosynthesis pathway, which reinforced oxidative stress scavenging and relieved folate-associated selective pressure, thereby mitigating ARGs dissemination. In addition, cyanobacteria-derived photosynthate favored autotrophic metabolism within the bacterial consortium, which reduced the abundance of genes encoding energy-dependent efflux pump transporters and consequently constrained the propagation of energy-intensive ARGs. Collectively, these findings highlight a cyanobacteria-mediated route to attenuate ARGs during prolonged ICPB operation and provide guidance for designing photocatalysis-coupled cyanobacterial biofilms for sustainable wastewater treatment. Download: Download high-res image (170KB) Download: Download full-size image