Effects Of Nano-zerovalent Iron On Antibiotic Resistance Genes During Livestock Waste Composting

Antibiotics and heavy metals are used as feed additives in animal breeding,which induce the emergence of resistant bacteria in the guts of animals.These resistant bacteria are excreted with the feces,which results in animal manure is an important reservoir of antibiotic resistance genes?ARGs?.ARGs spread among different microbial species via horizontal gene transfer?HGT?,and mobile genetic elements?MGEs?are the main medium of HGT.The agricultural use of aerobic composting products is an important way for ARGs to disseminate in the environment.Nano-zerovalent iron?n ZVI?has catalytic reduction and adsorption functions for antibiotics and heavy metals,and it's widely used in pollution control.Therefore,this study investigated the effects of adding n ZVI at 0,100,and 1000mg·kg^-1 on the physical and chemical properties,ARGs,MGEs and bacterial community during swine manure composting.Then,the relationship between ARGs and bacterial communities and environmental factors was analyzed.In addition,the microbial mechanism of n ZVI on ARGs was explored.The main results and conclusions are as follows:?1?The temperature of all treatments kept above 50?for more than 5 days,and the GI index exceeded 80%,which meets the requirements of harmlessness.The addition of n ZVI increased the content of NH₄⁺-N in the compost product,reduced the content of bio-Cu,and promoted compost maturation.?2?Aerobic composting reduced the abundance of 9 ARGs and 4 MGEs,with a decrease of 0.31-2.38 logs.Under n ZVI at 100 mg·kg^-1,the compost product had the most reduction effect on sul1,sul2,dfr A7,erm F,erm X,int I2 and Tn916/1545.Network analysis showed most of the ARGs have strong correlations with MGEs.Therefore,100 mg·kg^-1n ZVI can weaken the dissemination risk of ARGs by reducing the abundance of MGEs.?3?Firmicutes,Proteobacteria,Bacteroidetes,and Actinobacteria were the four dominant phylas in the composting process.The bacterial communities changed significantly throughout the whole composting process.Network analysis revealed 17 bacterial genera as potential host bacteria for ARGs and MGEs.RDA analysis showed that bacterial communities and MGEs mainly explained the variation in the ARG profiles.In summary,the addition of n ZVI promoted compost maturation and reduced the content of bio-Cu in compost products.The addition of 100 mg·kg^-1 n ZVI can effectively reduce the abundance of ARGs and MGEs in compost products.Bacterial communities and MGEs mainly affected the changes of ARGs.The addition of n ZVI can reduce the abundance of potential host bacteria,and decrease the spread of ARGs by inhibiting horizontal gene transfer.