Degradation of Antibiotic Resistance Genes and Mobile Genetic Elements in Dairy Manure Anaerobic Digestion

Abstract:

Antibiotic resistance genes (ARGs) are emerging contaminants causing serious global health concern. Dairy manure is considered as a reservoir of ARGs, and the extensive use of manure as fertilizers in croplands could transfer ARGs to the environment. To understand the effect of anaerobic digestion as a potential treatment in controlling ARGs, we conducted lab scale anaerobic digestion using filtered fresh manure under four temperatures (28, 36, 44, 52 °C) for 30 days. Abundance of three ARGs were studied by quantitative PCR: sulfonamide resistance gene (sulII), tetracycline resistance genes (tetW), macrolide-lincosamide-streptogramin B (MLSB) superfamily resistance genes (ermF). Three other genes were also studied including two mobile genetic elements (MGEs) genes (integrase gene intI1, transposase gene tnpA), which were responsible for dissemination of ARGs by horizontal gene transfer (HGTs), and 16S rRNA gene, which represented total bacterial biomass. According to the results, anaerobic digestion was an effective treatment to reduce ARGs and MGEs from dairy manure. However, thermophilic anaerobic digestion did not necessarily achieve better removal of ARGs and MGEs when compared with moderate and mesophilic temperatures. A modified Collins–Selleck model well fitted the decay of genes over time, and the fastest reduction rate was reached in the beginning of digestion (especially first 5 days) and then slowed down over time. This research helps to understand the effectiveness of anaerobic digestion as a potential treatment method to reduce ARG contaminations in dairy manure, as well as to provide a mathematical model to optimize treatment condition/time for attenuations of ARGs.