摘要

    放牧有望对草原生态系统中的抗生素抗性基因（ARG）产生重大影响。但是，放牧对草原土壤中ARGs组成的确切影响仍不清楚。对于长期放牧的草原土壤尤其如此。在这里，我们调查了长期历史放牧（13-39年）和相应的未磨砂样品的土壤中的ARGs和细菌群落组成。结合使用gun弹枪宏基因组学，扩增子分析和相关的土壤理化数据，我们提供了有关草地土壤中ARGs结构的新颖见解。有趣的是，我们的分析表明，长期的历史放牧对草原土壤中ARGs的组成没有影响。在放牧和未绿化地区平均发现了378种抗药性RGS，对14种主要抗生素具有抗药性（80％）。放线菌，变形杆菌和酸性细菌是这些土壤中最普遍预测的宿主，也显示出具有多重抗性ARGs的遗传能力。我们的结果表明，细菌群落组成对ARGs的积极影响可以通过影响MGEs来控制。通过影响细菌间水平基因转移的频率，土壤性质对ARGs的组成具有直接影响。在S. grandis草原草原上发现了十二种新颖的ARG，这表明不同的植被类型可能会引起土壤ARG的转变。总体而言，这些发现表明，土壤特性，植物和微生物在塑造草地上的ARG模式方面起着至关重要的作用。这些数据共同为了解草原的环境抗生素抗性奠定了坚实的基础。

    Grazing is expected to exert a substantial influence on antibiotic resistance genes (ARGs) in grassland ecosystems. However, the precise effects of grazing on the composition of ARGs in grassland soils remain unclear. This is especially the case for grassland soils subject to long-term grazing. Here, we investigated ARGs and bacterial community composition in soils subject to long-term historic grazing (13–39 years) and corresponding ungrazed samples. Using a combination of shotgun metagenomics, amplicon analyses and associated soil physicochemical data, we provide novel insights regarding the structure of ARGs in grassland soils. Interestingly, our analysis revealed that long-term historic grazing had no impacts on the composition of ARGs in grassland soils. An average of 378 ARGs, conferring resistance to 14 major categories of antibiotics (80%), were identified in both grazing and ungrazed sites. Actinobacteria, Proteobacteria and Acidobacteria were the most prevalent predicted hosts in these soils and were also shown to harbour genetic capacity for multiple-resistant ARGs. Our results suggested that positive effects of bacterial community composition on ARGs could potentially be controlled by affecting MGEs. Soil properties had direct effects on the composition of ARGs through affecting the frequency of horizontal gene transfer among bacteria. Twelve novel ARGs were found in S. grandis steppe grasslands, indicating that different vegetation types might induce shifts in soil ARGs. Collectively, these findings suggest that soil properties, plants and microorganisms play critical roles in shaping ARG patterns in grasslands. Together, these data establish a solid baseline for understanding environmental antibiotic resistance in grasslands.

    https://www.sciencedirect.com/science/article/abs/pii/S004896972036736X