Effect of biochar amendment on the alleviation of antibiotic resistance in soil and phyllosphere of Brassica chinensis L.

The increasing prevalence of antibiotic resistance is a global threat to public health. Antibiotic resistance genes (ARGs) in soil have been demonstrated to be able to enter food chain. Strategies to mitigate the spread of antibiotic resistance from soil to crops are of great importance for food safety and human health. Soil amendment with biochar is a widely used approach to improve soil fertility. However, the impact of biochar on mitigating antibiotic resistance of soil and organically produced vegetables that are eaten raw is largely unknown. To gain insights into this impact, pot experiments planting Brassica chinensis L. in soil amended with biochar were conducted and antibiotic resistance genes (ARGs) were characterized by HT-qPCR targeting almost all major classes of ARGs and 10 mobile genetic elements (MGEs) marker genes. A total of 131 ARGs and 9 MGEs in soil and phyllosphere samples were identified. After biochar amendment, the abundance of ARGs was significantly decreased in non-planted soil. By comparison, no significant decrease of ARGs was found in rhizosphere and phyllosphere, indicating that vegetable planting affected antibiotic resistome in biochar-amended soil. To understand this effect, bacterial phylogeny structures within soil and phyllosphere were analyzed and found to correlate with their respective resistome, indicating that planting can influence the effect of biochar on soil antibiotic resistome by altering microbial community compositions. Structure equation models further revealed that a higher bacterial diversity corresponded to a decreased ARGs content. These results suggested that biochar amendment alone was not sufficient enough to alleviate ARGs level in planted soil and crops, instead, maintaining or increasing soil microbial diversity is potentially more useful in mitigating ARG spread and accumulation.