Exogenous additives reshape the microbiome and promote the reduction of resistome in co-composting of pig manure and mushroom residue

Comprehensive understanding of the microbiome and resistome evolution in compost is crucial for guaranteeing the safety of organic fertilizers. Current studies using different composting systems and sequencing technologies have yielded varying conclusions on the efficacy of exogenous additives (EAs) in reducing antibiotic resistance genes (ARGs) in compost. This study employed metagenomics to investigate the impact of various EAs on microbial communities, ARGs, their coexistence with mobile genetic elements (MGEs), and ARG hosts in co-composting. Our results demonstrated that EAs significantly reshaped the microbial communities and facilitated a notable reduction in total ARG abundance and diversity, primarily by decreasing core ARGs. Cooperative rather than antagonistic relationships among bacteria. The RA changes in total ARGs are mainly caused by a decrease in the prevalence of core ARGs. Furthermore, EAs showed significant efficacy in reducing clinical ARGs, including cfxA, tetX1, cfxA6, vanA, and aac (6′)-Ib', with diatomite (5 %) and zeolite (5 %) being the most effective. The effect of EAs on ARGs and microbial community assembly were stochastic processes. Composting stage and EAs jointly reduced the association between ARGs and MGEs in the composting system. The reduction of ARGs attributed to a decreased abundance of potential pathogenic ARG-associated hosts and diminished associations with MGEs. In conclusion, EAs present a straightforward and effective approach for promoting ARGs reduction in compost, offering crucial insights for assessing the environmental risks associated with the release of agricultural ARGs.