Response behavior of antibiotic resistance genes to zinc oxide nanoparticles in cattle manure thermophilic anaerobic digestion process: A metagenomic analysis

•Anaerobic digestion of cattle manure containing zinc oxide nanoparticles (ZnO NPs) was studied.•A metagenomics-based approach to explore behaviors of antibiotic resistance genes (ARGs) was used.•ZnO NPs reduce ARGs’ risk in cattle manure anaerobic digestion (55 °C) by abundance.•ZnO NPs pose significant effects on ARGs mechanisms and decrease potential hosts.•Declined chemotaxis by ZnO NPs induces a possible inhibition on ARGs’ propagation. This work investigated the metagenomics-based behavior of antibiotic resistance genes (ARGs) during cattle manure anaerobic digestion with zinc oxide nanoparticles (ZnO NPs) that are commonly used as animal feed additives. The 6.6% decrease in total ARGs abundance while remained unchanged ARGs diversity with ZnO NPs (5 mg/g total solid), suggested ZnO NPs may mitigate ARGs risk by abundance. Also, ZnO NPs affected ARGs with mechanisms specifically of antibiotic inactivation and antibiotic target change, and declined potential hosts’ abundance (bacterial genus Ruminiclostridium, Riminococcus, and Paenibacillus) which mainly contributed to the decreased ARGs’ abundance. Besides, microbial chemotaxis decreased by 17% with ZnO NPs compared to that without nanoparticles indicated a depression on potential hosts, who could develop the mechanism to adapt to altered digestion conditions, which probably inhibited the ARGs’ propagation. These findings are important to promote understanding of the potential ARGs risks in treatments of livestock wastes containing animal feed additives.