Root Exudates Are Linked to Antibiotic Resistance Gene Variation by Modulating Rhizosphere Microbial Community Assembly Under Swine Wastewater Irrigation

Background: Irrigation with swine wastewater may increase the dissemination risk of antibiotic resistance genes (ARGs) in the rhizosphere and alter root exudate composition. However, the relationship between root exudates and ARG dynamics under swine wastewater irrigation remains poorly understood. This study therefore aimed to clarify how root exudates are connected with ARG dynamics under swine wastewater irrigation. Methods: To address this, untargeted metabolomics and metagenomic sequencing were combined to characterize rhizosphere ARG composition, microbial community structure, and root exudate profiles in different soybean cultivars under swine wastewater irrigation. Results: The results showed that irrigation water source and soybean cultivar were associated with variation in soil ARG composition and changes in plant root metabolic profiles. Under wastewater irrigation, the relative abundances of secondary metabolites in root exudates were generally elevated, particularly those of organic nitrogen compounds and organic oxygenated compounds. Cultivar-related variation remained evident in rhizosphere microbial communities and ARG profiles, and differences in exudate composition among cultivars became smaller. Irrigation water source and soybean cultivar were associated with changes in ARG dynamics. This association was mainly linked to variation in rhizosphere microbial community structure rather than direct effects of root exudates on ARGs. Xanthine and 3-isobutylpentanedioic acid, identified as key root exudates, increased under wastewater irrigation and were related to variation in the potential ARG host genus SCGC-AG-212-J23 and the related ARGs. In contrast, 5-methylheptan-3-one decreased under wastewater irrigation and was correlated with variation in SCGC-AG-212-J23, Gp6-AA40, and the related ARGs. Conclusions: Swine wastewater irrigation and soybean cultivar altered root metabolism, which were linked to variation in rhizosphere microbial communities. These changes may have collectively contributed to shifts in rhizosphere ARGs. This could provide a basis for understanding the ecological relationships among root exudates, microorganisms, and ARGs under swine wastewater irrigation.