Pathogenic bacteria contribute to antibiotic resistance genes dissemination in microcystin-LR exposed intestine of zebrafish.

Cyanobacterial blooms and antibiotic resistance genes (ARGs) in aquatic ecosystems are emerging public health concerns. Microcystin-LR (MC-LR), a representative cyanotoxin released from cyanobacterial blooms, has poorly understood mechanisms regarding its influence on the dissemination of ARGs. In this study, zebrafish were exposed to MC-LR at environmentally relevant concentrations to investigate the mechanisms underlying the influence of MC-LR on the prevalence and dissemination of ARGs in the intestine, with a focus on intestinal microbiota and pathogenic bacteria. Overall, MC-LR exposure significantly increased the total abundance of ARGs (p < 0.01). Microbial assembly taxa explained the largest proportion of ARGs variation (25.4 %), substantially more than mobile genetic elements (20.6 %) and oxidative stress (5.7 %). Specifically, pathogenic assembly taxa showed stronger correlations with ARGs than whole microbial taxa (Mantel p = 0.001 vs. 0.005; Procrustes p < 0.002 vs. < 0.004). Furthermore, the pathogenic community was a direct and significant determinant of ARGs dissemination compared to the non-pathogenic community (PLS-PM goodness-of-fit: 0.971 vs. 0.936; p < 0.05 vs. > 0.05). More concerning, MC-LR exposure promoted the dominance of the pathogenic biomarker Vibrio, which significantly contributed to ARGs variation. This study highlights the dominance of pathogenic bacteria in the prevalence of ARGs under MC-LR exposure, indicating that potential environmental risks to public health should be re-evaluated in cyanobacteria-contaminated aquatic ecosystems.