The reduction of antibiotic resistance genes in lettuce and soil amended with sewage sludge compost

Sludge compost product (SCP) application may lead to an increase in antibiotic resistance genes (ARGs) in crops cultivated in soil with a low background of ARGs. Yet, the impact of SCP application on ARGs in crops cultivated in soils previously fertilized with manures remains unclear. Therefore, this study applied SCP to amend soil previously fertilized with manures and then cultivated lettuce to explore the variations of ARGs in soil and crops through pot experiments. After lettuce harvest, ARGs, and factors affecting ARGs, such as heavy metals, mobile genetic elements (MGEs), metal resistance genes (MRGs), and bacterial communities, were investigated. The results revealed that 2%-15% of SCP addition increased lettuce biomass by 1.92-2.27 times and strongly reduced the relative abundance of ARGs in both soils and lettuces. Furthermore, SCP addition resulted in significant alteration of bacterial communities in soil, lettuce phyllosphere and endophyte. The alteration of bacterial communities, particularly Proteobacteria and Firmicutes, explained the changes in ARGs in soil, lettuce phyllosphere and endophyte. Notably, MGEs did not contribute to the dissemination of ARGs in both soil and lettuce, while MRGs co-occurred with ARGs in soil and lettuce endophyte. Additionally, a SCP addition rate of 5% is recommended in agricultural use because it not only increased lettuce biomass and reduced the relative abundance of ARGs by 53.59% in lettuce, but also ensured that heavy metals in lettuce grown in 5% SCP -amended soil met the requirement of China’s national standards. This study provides valuable insights into the application of ARGs in agriculture soils fertilized with manures.