Elucidating the effect of microbial inoculum and ferric chloride as additives on the removal of antibiotic resistance genes from chicken manure during aerobic composting

[Display omitted] •Microbial agent and ferric chloride improved microbial activity in compost.•Two additives effectively inhibited the enrichment of persistent “sul” ARGs.•Tn916/1545 and intI1 were the main genetic elements affecting the spread of ARGs.•Combined application of two additives is a promising composting strategy. This experiment investigated the effect of adding a microbial inoculum (M) and ferric chloride (F) on the fate of antibiotic resistance genes (ARGs) during chicken manure composting. Adding M and F improved the microbial activity in the compost and facilitated the removal of ARGs, whereas the combined treatment achieved the best results, especially in reducing the enrichment of sul resistance genes. Tn916/1545 and intI1 were important genetic elements that affected the transfer of ARGs, and Tn916/1545 was closely related to the transfer of tetM, tetW, and ermQ in Firmicutes. Kyoto Encyclopedia of Genes and Genomes functional predictions indicated that M and F could reduce the abundance of membrane transport and signal transduction molecules in the compost products. Thus, these findings suggest that the combined application of M and F is a promising strategy that could potentially inhibit the transfer of ARGs during composting.