Profiling of intracellular and extracellular antibiotic resistance genes in municipal wastewater treatment plant and their effluent-receiving river.

The presence of antibiotic resistance genes (ARGs) and heavy metal resistance genes (MRGs) in extracellular and intracellular DNA (eDNA and iDNA) has received considerable attention in recent years owing to the potential threat to human health and the ecosystem. As a result, we investigated six ARGs, three MRGs, and two mobile genetic elements (MGEs) in the municipal wastewater treatment plant (MWWTP) and its adjacent environments. Results revealed that the absolute abundances of eARGs and eMRGs were lower than iARGs and iMRGs in MWWTP. By contrast, eARGs and eMRGs were higher in river sediments. Among ARGs, aminoglycoside resistance genes (aadA) was the most abundant gene (3.13 × 10 to 2.31 × 10 copies/mL in iDNA; 1.27 × 10 to 7.23 × 10 copies/mL in eDNA) in MWWTP, while zntA gene (9.4 × 10 to 3.97 × 10 copies/mL in iDNA; 3.2 × 10 to 6 × 10 copies/mL in eDNA) was amongst the MRGs. Notably, intI1 was enriched and positively correlated with iDNA (tetA, sul1, blaCTX-M, ermB, and merA) and eDNA (blaCTX-M, ermB, and merA), demonstrating its function in the proliferation of resistance genes. This widespread distribution of ARGs, MRGs, and MGEs in MWWTP and its adjacent river sediments will help clarify the transmission routes within these environments and provide a theoretical basis for better monitoring and mitigation of such dissemination.