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Abstract In the present study, the occurrence and abundance of tetracycline resistance genes (TRGs) were investigated in a paddy soil after continuous application of composted swine manure (9.0t/hm2 and 4.5t/hm2) for 6years. Nine classes of TRGs (tetW, tetB(P), tetO, tetS, tetC, tetG, tetZ, tetL, and tetX) was detected in the soil applied with composted swine manure, among which the absolute abundance of tetG, tetL, tetB(P), tetO, tetW were significantly increased, and there were significantly more copies of tetB(P), tetW, tetO in the soil treated with 9.0t/hm2 composted swine manure than with 4.5t/hm2, while the absolute abundance of tetZ, tetC and tetS was not influenced. There was no significant difference in the relative abundance of detected TRGs distributed with a depth of 0~5cm, 5~10cm, and 10~20cm in the same treatment. The relative abundance of tetG, tetL, tetB(P) and tetO was significantly increased in the soils treated with composted swine manure, but only tetO was influenced by the application weight of the manure. The results suggested that the residual TRGs in the composted swine manure shed further influence on the TRGs pool in soils with rice-wheat crop rotation, absolute and relative abundance of tetG, tetL, tetB(P) and tetO being significantly increased after continuous application of composted swine manure. Therefore, optimization of composting strategies is urgently needed to efficiently reduce the content of antibiotic resistance genes in the composted swine manure.
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