Metagenomic indications of potential pathogen-associated and antibiotic resistance risks following UV-chlorine disinfection in sprout production.

Hydroponic agriculture commonly relies on low-pressure UV combined with chlorination (LPUV-chlorine) disinfection for water reuse, yet its impacts on non-coliform pathogens and associated resistance risks remain insufficiently understood. Here, metagenomic analysis of a commercial sprout production system revealed that LPUV-chlorine treatment did not completely remove pathogen-associated DNA signals and was associated with an increased relative abundance of Pseudomonas aeruginosa, accompanied by increased abundance of antibiotic resistance genes (ARGs) and virulence factor genes (VFGs). The relative abundances of VFGs related to biofilm formation and exoenzyme activity increased by 16∼18-fold compared to source water (SW), while β-lactam resistance genes showed marked increases in relative abundance. Network analysis revealed statistical associations between several pathogen-associated taxa and ARG profiles but did not establish their genomic hosts or transfer pathways. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis further revealed higher relative representation of genes associated with two-component systems and flagellar assembly, suggesting potential stress-adaptive functions and preferential persistence. In contrast, medium-pressure UV (MPUV) achieved ≥ 4-log reductions of P. aeruginosa, Escherichia coli, and Salmonella enterica within seconds, with 40.24%, 2.29%, and 26.44% lower fluence than LPUV, respectively. Transcriptomic analysis revealed decreased expression of selected virulence-associated genes and increased expression of phage-associated genes, suggesting potential effects on virulence-related functions and prophage responses. These findings highlight a potential pathogen-selection risk under LPUV-chlorine disinfection and indicate MPUV as a promising chlorine-free microbial risk control strategy in hydroponic water reuse systems.