Polystyrene nanoparticles and phosphorus sources jointly modulate antibiotic resistance gene enrichment in...

The regulatory mechanisms of antibiotic resistance genes (ARGs) in freshwater microalgae-bacteria systems under combined nutrient-nanoplastic stress remain poorly understood. Herein, we investigated the combined effects of phosphorus (P) sources (inorganic phosphate (IP), adenosine monophosphate (AMP), and phytic acid (PA)) and polystyrene nanoplastics (PS-NPs; 10 and 100 mg/L) on the Chlorella pyrenoidosa‑bacteria system. Results showed that P utilization efficiency followed the order IP > AMP > PA. PS-NPs exerted concentration-dependent effects: low concentrations activated adaptive pathways (including glutathione metabolism) to maintain homeostasis, whereas high concentrations disrupted photosynthesis and membrane integrity, reducing chlorophyll a levels by 20.84%-58.89% and suppressing algal growth. Quantitative PCR and microbial sequencing confirmed that P supplementation increased ARG abundances by 37.58%-59.34%, with organic phosphorus groups harboring higher ARG levels than those of IP groups. Low PS-NP concentrations further promoted ARGs by 16.21% via mobile genetic elements (intI1 and tnpA-04) that mediate horizontal gene transfer, whereas high PS-NP concentrations reduced ARGs by 2.70% through diversity suppression. Proteobacteria dominated, with Brevundimonas and Aquimonas identified as potential ARG hosts. Microbial community assembly was a primary driver of resistome profiles, alongside mobile genetic elements and P metabolism. These findings highlight that nutrient-nanoplastic interactions accelerate ARG propagation in microalgae-bacteria systems, providing insights for managing environmental antibiotic resistance.