Ni Contaminated soil antibiotic resistance genes study

Heavy metal contamination is assumed to function as a selection pressure in the proliferation of antibiotic resistance, however, our knowledge of the heavy metal-induced changes of antibiotic resistance is lacking in a long-term basis. Using high-capacity quantitative PCR array and Illumina sequencing, we investigated the responses of a wide spectrum of soil antibiotic resistance genes (ARGs) to 4-5 year nickel exposure (0-800 mg kg-1 22 ) in two well manipulated experimental sites. In total, 149 unique ARGs were detected in the two sites, with genes conferring resistance to multidrug and ß-lactam as the most prevailing ARG types. The frequencies and relative abundance of ARGs tended to increase along the gradient of increasing nickel concentrations, with the highest values recorded in the treatments amended with 400 mg nickel kg-1 27 soil. The abundance of mobile genetic elements (MGEs) showed increasing tendency with increasing nickel levels and was significantly correlated with ARGs, suggesting that nickel exposure might enhance the mobility potential of ARGs. Network analysis revealed significant association between ARGs and MGEs, with the integrase intI1 gene having the most frequent interactions with other co-occurring ARGs. Structural equation models demonstrated that the nickel-induced changes of ARGs were mainly driven by nickel bioavailability and MGEs, rather than by bacterial communities. Taken together, we provide field-based evidence that long-term nickel exposure significantly increased the diversity, abundance, and mobility potential of soil antibiotic resistance, and highlight the health risk of multi-resistant ARGs selected by heavy metal in polluted environments.