Co-exposure to cyazofamid and polymyxin E: Variations in microbial community and antibiotic resistance in the soil-animal-plant system

Abstract

Human activity is accelerating the emergence of fungal pathogens, prompting substantial efforts to discover novel fungicides. Meanwhile, the runoff and spray drift from agricultural fields adversely affect aquatic and terrestrial nontarget organisms. However, few studies have examined the effects of co-contamination by agrochemical fungicides and pharmaceutical antibiotics on microorganisms and antibiotic resistance genes (ARGs) in the soil-animal-plant system. To further explore the mechanisms, an investigation was conducted into the individual and combined effects of a widely used fungicide (cyazofamid, CZF) and a last-resort antibiotic (colistin, polymyxin E, PME) in the soil-earthworm-tomato system. This study revealed that CZF and PME co-contamination exerted synergistic toxicity, significantly reducing earthworm survival and inhibiting tomato growth. This study found that the structure of microbial communities was more severely disturbed by the fungicide CZF than by the antibiotic PME, with the most severe impact being that of CZF + PME co-contamination. Fungicides and antibiotics had significantly distinct effects on bacterial functional pathways: CZF and CZF + PME treatments enhanced compound degradation, whereas PME treatments promoted biological nitrogen cycling. Moreover, co-contamination significantly increased the abundance of insertional and plasmid-associated genes and number of total ARGs in bulk and rhizosphere soil. In addition, the relationships between bacterial communities and the antibiotic resistome were investigated. The analysis revealed that Gram-positive bacteria (Sporosarcina, Bacillus, and Rhodococcus) capable of resistance and degradation, as well as the genes MexB (multidrug) and aadA2 (aminoglycoside) were enriched. Taken together, interactions between co-pollutants can significantly increase toxicity levels and the risk of ARG proliferation. The findings provide new insights into the potential impacts of co-contamination in complex real-life environments, such as soil–animal–plant systems.