Sulfate addition enhanced antibiotic resistance in lake sediments by enriching resistant bacteria and promoting the potential of horizontal gene transfer.

Lake sediments represent a typical reservoir of antibiotic resistance genes (ARGs), an emerging contaminant. As a key nutrient for sediment microorganisms, elevated sulfate levels can profoundly influence sulfur cycling and related microbial processes. However, the impact of sulfate loads on the profiles of ARGs in lake sediments remains poorly understood. This study utilized a microcosm experiment to examine how sulfate addition at various concentrations (200, 400, and 600 mg/kg dry weight) affects the sediment resistome, via metagenomic analysis. Sulfate addition significantly increased sediment sulfides and the relative abundance of sulfate-reducing genes (SRGs). Notably, the high sulfate treatment (600 mg/kg) resulted in a significant rise in the relative abundance of ARGs, virulence factor genes (VFGs), and mobile genetic elements (MGEs), indicating an increased potential for resistance dissemination under high sulfate loading. The relative abundance of horizontal transfer related genes, including those mediating cell membrane permeability and type IV secretion system, was enhanced by sulfate addition, potentially promoting ARG dissemination. Linear regression identified strong positive relationships between the abundance of ARGs and abundances of both MGEs and VFGs. Sulfate addition enriched specific antibiotic-resistant bacteria (ARBs) carrying SRGs that were identified via network analysis. The genera Burkholderia, JACDDX01, and Hylemonella showed marked enrichment, with increases of 16.7 %, 13.2 %, and 94.6 %, respectively. Overall, the rise in ARG abundance under sulfate addition shows close links to specific ARBs and enhanced horizontal transfer. These findings have implications for understanding sulfate-driven changes in sediment resistome and assessing environmental risk in sulfate-enriched lake ecosystems.