Nicosulfuron-driven antibiotic resistance in corn silage: Effect and its mitigation by zinc oxide nanoparticles.

Antibiotic resistance genes (ARGs) present in animal feed represent a significant threat to human health via the food chain, and pesticide application in crop production may further accelerate the ARGs dissemination. Corn silage, a primary forage for herbivorous livestock, has been shown to harbor diverse ARGs; however, the impact of pesticide-induced stress and potential mitigation strategies on ARG proliferation remains poorly understood. This study investigated the mechanistic link between nicosulfuron exposure and ARG dynamics in corn silage, as well as the mitigating effects of zinc oxide nanoparticles (ZnO NPs) on ARG under nicosulfuron exposure using metagenomic sequencing and high-throughput quantitative PCR. Nicosulfuron exposure increased (P < 0.05) ARG diversity and abundance, enriched (P < 0.05) ARG-hosting genera such as Pantoea, Escherichia, and Klebsiella, and intensified (P < 0.05) the correlation between ARGs and mobile genetic elements (MGEs). Additionally, it disrupted microbial metabolic pathways and elevated (P < 0.05) the ARG-associated risk index in corn silage. Conversely, ZnO NPs alleviated (P < 0.05) these effects by reducing the abundance of key ARGs-bacA, tetM, and ermB, enhancing microbial diversity, promoting beneficial genera such as Levilactobacillus and Companilactobacillus, and decreasing the complexity of ARG-MGE-microbe co-occurrence networks in corn silage under nicosulfuron exposure. Structural equation modeling indicated that there was a significant association between bacterial community and ARGs proliferation, and it had the strongest explanatory power for the variation in ARGs abundance, followed by MGEs. These findings underscore the ecological risks associated with nicosulfuron and demonstrate that ZnO NPs have the potential to mitigate ARGs dissemination in pesticide-contaminated silage. However, this potential does not qualify ZnO NPs as an effective strategy, and their role in promoting safer forage production still requires further evaluation.