Exploring the dynamics of antibiotic resistome on plastic debris traveling from the river to the sea along a representative estuary based on field sequential transfer incubations

The environmental risks arising from ubiquitous microplastics or plastic debris (PD) acting as carriers of antibiotic resistance genes (ARGs) have attracted widespread attention. Enormous amounts of plastic waste are transported by rivers and traverse estuaries into the sea every year. However, changes in the antibiotic resistome within the plastisphere (the biofilms formed on PD) as PD travels through estuaries are largely unknown. In this study, we performed sequential migration incubations for PD along Haihe Estuary to simulate the natural process of PD floating from rivers to the ocean. Metagenomic sequencing and analysis techniques were used to track microbial communities and antibiotic resistome on migrating PD and in seawater representing the marine environment. The total relative gene copies of ARGs on traveling PD remained stable. As migration between greatly varied waters, additional ARG subtypes were recruited to the plastisphere. Above 80 % ARG subtypes identified in the plastisphere were persistent throughout the migration, and over 30 % of these persistent ARGs were undetected in seawater. The bacterial hosts composition of ARGs on PD progressively altered as transported downstream. Human pathogenic bacteria carrying ARGs (HPBs-ARG) exhibited decreasing trends in abundance and species number during transfer. Individual HPBs-ARG persisted on transferred PD and were absent in seawater samples, comprising Enterobacter cloacae, Klebsiella pneumoniae, Mycobacterium tuberculosis, and Vibrio parahaemolyticus. Based on all detected ARGs and HPBs-ARG, the Projection Pursuit model was applied to synthetically evaluate the potential risks of antibiotic resistance on migrating PD. Diminished risks on PD were observed upon the river-to-sea journey but consistently remained significantly higher than in seawater. The potential risks posed to marine environments by drifting PD as dispersal vectors for antibiotic resistance deserve greater attention. Our results provide initial insights into the dynamics or stability of antibiotic resistome on PD crossing distinct aquatic systems in field estuaries.