Silicon dioxide nanoparticles have contrasting effects on the temporal dynamics of sulfonamide and beta-lactam resistance genes in soils amended with antibiotics

Nanoparticles (NPs) and antibiotic resistant genes (ARGs), as emerging environmental contaminants, have been reported to be accumulated in the soil environment. The use of NPs have raised increasing concerns about their environmental impacts, but the combined effect of NPs and antibiotics on ARGs remains less understood. Here, we established laboratory microcosms to explore the impacts of different concentrations of SiO2 NPs on beta-lactam and sulfonamide resistance genes in soils amended with beta-lactam or sulfonamide. Illumina sequencing and quantitative PCR revealed that the addition of NPs increased the bacterial community diversity but had no significant effects on the bacterial abundance. Moreover, NPs and sulfonamide jointly increased the abundances of sulfonamide resistance genes, while the exposure of NPs and beta-lactam decreased beta-lactam resistance genes. The detected ARGs were associated closely with two mobile genetic elements (MGEs, the tnpAand intI1 genes), indicating that MGEs may contribute to the dissemination of ARGs. Correlation analysis indicated the shifts in potential bacterial hosts and the frequency of horizontal gene transfer were important factors explaining the patterns of ARGs. Furthermore, structural equation models indicated that NPs exposure decreased the abundances of beta-lactam resistance genes by driving changes in bacterial community and MGEs, whereas the increased abundances of sulfonamide resistance genes were mainly associated with the bacterial community, diversity and MGEs mediated by NPs and antibiotics. These results suggested that the combined effects of NPs and antibiotics on soil bacterial resistance were different due to the types of antibiotics.