Insights into the Mechanisms Driving the Dynamics of Antibiotic Resistance Genes During Pig Manure Composting

As a widely adopted approach for the resource utilization of pig manure, the ability of composting to reduce risk pollutants such as antibiotic resistance genes (ARGs) has gained significant attention. Temperature plays a pivotal role in determining the effectiveness of composting, with the maximum composting temperature and duration of high temperature being key indicators of compost quality. This study investigated the influences of adjusting the thermophilic stage on the dynamics of ARGs during pig manure composting. The results revealed that the adjustment strategies of thermophilic stage controls (i.e., prolonging the duration of the thermophilic stage or raising the maximum temperature) slightly promoted the absolute abundance of total ARGs by 0.72-0.99 logs, whereas their relative abundance was notably reduced by 49.7~64.1%. Some ARGs (i.e., tetW, tetO, tetM, fexA, fexB, ermA, and ermB) could be effectively removed by the composting, whereas sulI, sulII, aadA, and tetL enriched the horizontal gene transfer and diversified the potential bacterial hosts. The variations of ARG profiles and the succession of bacterial communities could be divided into two stages, which coincided with the organic carbon (OC) content (82%). The nutrient factors, especially the OC content, were strongly relative to several ARGs, implying that the organic nutrient could be an important driving force in shaping ARG distribution, potentially by influencing bacterial community succession. Three potential opportunistic pathogens (Mycobacterium, Bordetella and Bacillus) exhibited positive correlations with enriched ARGs, highlighting the potential risks of the dissemination of antibiotic-resistant pathogens though the application of compost products.