Antibiotic resistance profile of nitrogen-metabolizing microbes in anoxic‒oxic processes for swine wastewater treatment

Abstract The anoxic-oxic (A/O) process is the most common biological method for removing nitrogen (N) from wastewater, but the antibiotic resistance profile of N-metabolizing microbes in A/O processes remains largely underexplored. Here we demonstrated a significant positive correlation between various types of N-metabolizing genes and antibiotic resistance genes (ARGs) in swine wastewater A/O processes across China. We assembled 180 high-quality genomes of dominant N-metabolizing microbes (12.6% of the total metagenome-assembled genomes), all harboring transcriptionally active ARGs. And Pseudomonas was identified as the primary N-metabolizing genus and major ARG host. Among 1110 culturable N-metabolizing isolates, 22.34% were Pseudomonas strains showing high N removal capacity and multi-antibiotic resistance. Moreover, plasmid-mediated ARG transfer further heightened resistance risks. Overall, these findings highlight a significant ARG risk among predominant N-metabolizing microbes in A/O treatment processes, underscoring the urgency of balancing N removal performance with resistance control in wastewater treatment processes.