Metagenomic insights into antibiotic resistance genes in cyanobacterial blooms of plateau lakes: spatial patterns, environmental associations, and risk implications

Harmful cyanobacterial blooms (cyanoHABs) significantly threaten plateau freshwater lakes, impacting drinking water safety and interacting with antibiotic resistance genes (ARGs). However, the mechanisms behind this interaction are still unclear. In this study, we used metagenomic techniques and antibiotic exposure experiments to investigate ARGs distribution and driving factors in Erhai Lake during cyanoHABs. We identified 28 ARG subtypes (65 in total), with elfamycin and tetracycline ARGs being particularly enriched in sediment and overlying water. Dominant microbial phyla, such as Actinobacteria and Pseudomonadota , facilitated horizontal gene transfer (HGT) through co-occurrence networks, with transposases as key genes driving ARGs diffusion. Nutrient gradients enhanced ARGs spread by boosting Pseudomonadota proliferation, increasing mobile genetic elements (MGEs), and raising algal biomass, which co-enriched virulence factors (VFs) and ARGs. ARG environmental risk scores (ERS) showed spatial differences: high ERS in southern overlying water was linked to wastewater discharge and longer water retention, while peak ERS in northern sediment was tied to livestock farming and agriculture. Tetracycline exposure had concentration-dependent effects: low concentrations (10 ng/L) competitively inhibited ARG carriers (cyanobacteria), while high concentrations (100 ng/L) caused algal death, releasing organic matter and MGEs that promoted heterotrophic bacterial growth and ARGs’ HGT. This study offers valuable insights for managing antibiotic resistance in plateau lakes and highlights the need for targeted strategies to address nutrient-ARG interactions during cyanoHABs. • The ARGs in Erhai Lake exhibit dual - source driving characteristics. • Transposases serve as key mediators of ARGs' horizontal transfer. • Nutrients exert dual regulatory effects on the spread of ARGs. • Antibiotic exposure poses ecological risks that are concentration-dependent. This study shows how antibiotic resistance genes spread during blue-green algae blooms in plateau lakes and stresses the need to control nutrient inputs to curb their spread.