Manure sterilization reduced antibiotic resistance genes in lettuce endophytes

Livestock manure is commonly utilized as a fertilizer in agricultural system, potentially resulting in the dissemination of antibiotic resistance genes (ARGs) to plants. This raises concerns about the efficiency of manure treatment methods in reducing ARGs. Although sterilization treatment is frequently applied to mitigate the microbial loads, its efficacy in reducing ARGs remains unclear. This study investigated the impact of sterilized vs. unsterilized manure on the profiles of ARGs and bacterial community in a hydroponic lettuce system. After the 20-day cultivation period, 68 ARGs and 18 mobile genetic elements (MGEs) were identified. Manure sterilization not only promoted lettuce growth but also resulted in a reduction of ARG and MGE subtypes by 50.00%-86.21% in lettuce endophytes. Proteobacteria, Bacteroidota, and Firmicute were the dominant phyla, with a notable reduction of 70.05%-99.01% in Firmicutes by sterilization in lettuce endophytes. The predominant human pathogenic bacteria genera were Pseudomonas, Sphingomonas, and Bacillus, and sterilization effectively reduced the presence of Bacillus. Moreover, the estimated intake of ARGs in leaf endophytes ranged from 2.88 x 10(5) to 9.16 x 10(8) copies per day, including 6 high-risk ARGs. Manure sterilization reduced the association between high-risk ARGs and human pathogenic bacteria. The interaction between bacterial community and MGEs shaped ARG patterns with a contribution of 81.87%. Overall, these findings highlighted the critical role of sterilization in reducing ARGs in the manure used for hydroponic agriculture, providing guidance in waste management, crop safety, and public health.