Effects of adding corn straw and apple tree branches on antibiotic resistance genes removal during sheep manure composting.

The study investigates the effects of composting sheep manure with corn straw (CM) and sheep manure with apple tree branches (AM) on antibiotic resistance genes (ARGs) and microbial communities. The results indicate that AM treatment enables the compost pile to reach the high-temperature phase more quickly. The total phosphorus and total potassium content in AM treatment compost increased compared to the initial stage of composting, while CM treatment effectively enhanced the total nitrogen and total phosphorus content, and CM treatment compost was more conducive to reducing the compost's electrical conductivity. The relative abundance of total ARGs for sulfonamides, tetracyclines, and integrase genes in CM treatment compost were lower than in AM treatment compost. CM treatment was beneficial in reducing the relative abundance of sul1 and tetA-02 by 33.61% and 35.51%, respectively. Both treatments were effective in reducing the relative abundance of sul3 and intI2. The relative abundance of Chloroflexi and Proteobacteria in AM treatment decreased over time, while Bacteroidetes increased, which was opposite to the trend observed in CM treatment. There were significant correlations between the compost's physicochemical properties, bacterial communities, ARGs, and mobile genetic elements (MGEs). ARGs and MGEs can exist in multiple host bacteria, and various ARGs and MGEs can also be hosted in the same bacterium. Mantel analysis showed that the total organic matter, total phosphorus, and total potassium had the greatest contributions to the changes in ARGs and MGEs, while temperature and bacterial communities regulated ARGs by affecting MGEs. Obviously, adding corn straw is more effective in reducing the abundance of ARGs during the sheep manure composting.