Humus Soil Inhibits Antibiotic Resistance Gene Rebound in Swine Manure Composting by Modulating Microecological Niches.

Aerobic composting is widely used for the degradation of organic matter, simultaneously reducing the presence of antibiotic resistance genes (ARGs) in swine manure. However, the phenomenon of abundance rebound or even enrichment of ARGs is still a problem. The effect and mechanism of humus soil (Hs) on ARG reduction by adding it into the piles (0% for the control group (CK); 10% for S1 group; 20% for S2 group; and 30% for S3 group) after the thermophilic phase of composting was investigated. The results indicated that Hs promoted organic matter degradation and nitrogen loss. During days 15-36, the greatest reduction of 69.91% in total ARG abundance was observed in S2, while the abundance rebounded by 222.75% in CK and decreased only 13.71% in S3. With the 20% Hs addition, 85.42% abundance reduction for mobile genetic elements (MGEs) and 100% removal rates for A5, A9, 1, 2, and X were achieved. Moreover, the addition of Hs immediately changed the bacterial community structure of the substrate and varied the bacterial community successional direction in the treatments. Additionally, significantly positive correlations (|r| > 0.6; < 0.05) were found between the top 20 genera and ARGs. The potential host bacteria for ARGs changed from , , , and in CK to , , and in S2, highlighting the shift and reduction in host bacteria driven by Hs, which, in turn, influenced the abundance variations in ARGs. This study verified the feasibility of inhibiting the rebound of ARG abundance effectively by influencing the microecological niche in the pile, offering an approach for promoting a reduction in ARGs in animal wastes.