Effects of sub-inhibitory antibiotic exposure on elemental cycling genes in an aquatic microbial community

Understanding how low concentrations of antibiotics influence biogeochemical cycling mediated by aquatic microbes is essential for assessing the ecological risks of antibiotic pollution. Here we examined the responses of carbon, nitrogen, and sulfur cycling genes in an aquatic microbial community to trimethoprim, lincomycin, and their combined exposure across seven sub-inhibitory concentrations spanning three orders of magnitude. We found that while the diversity of elemental cycling genes remained largely unchanged, the abundance of associated metabolic pathways declined significantly under high antibiotic levels,particularly after seven days of exposure to 10 mg/L lincomycin or ≥ 1 mg/L trimethoprim-lincomycin combinations. Some elemental cycling genes increased in abundance under elevated antibiotic exposure, accompanied by concentration-dependent enrichment of antibiotic resistance genes (ARGs). Metagenomic assembly further revealed that enriched ARGs and cycling genes co-localized on the same contigs. In addition, antibiotic exposure reshaped the topological structure of molecular ecological networks among cycling genes, indicating altered microbial interactions and ecological processes. Together, these findings show that antibiotics not only enrich resistance determinants but also modulate the abundance of carbon, nitrogen, and sulfur cycling genes, underscoring the complex impacts of anthropogenic antibiotic pollution on microbially mediated biogeochemical cycles.