Effects Of Aerobic Composting On Antibiotic Resistance Genes In Pig Manure

In recent years,antibiotic resistance genes(ARGs)induced by the extensive use of antibiotics in the livestock and poultry breeding industry have accelerated the spread of antibiotic resistance.Composting,as a common method of innocuity,reutilization,and reduction for livestock and poultry manure,can promote the decomposition of organic matter,accelerate the process of humification,and have a good removal effect on some pollutants.In this project,we simulated the aerobic composting of pig manure under artificial control conditions,using the temperature of the compost as a control variable.The basic physical and chemical properties during composting were monitored to study the fluctuation and influencing factors of resistance genes in pig manure under different temperatures.The basic physical and chemical properties(including temperature,p H,electrical conductivity,germination index,total organic carbon,total nitrogen,total phosphorus)and heavy metal contents(Cu and Zn)in low-temperature,middle-temperature and high-temperature groups were monitored.The high-temperature group could significantly accelerate the compost maturation process.The contents of Cu and Zn decreased compared with the initial stage of composting(decreased by 0.50%-10.16%).High-throughput sequencing technology was used to analyze the succession of microbial community structure in compost samples.The results showed that Proteobacteria,Firmicutes,Bacteroidetes,and Actinobacteria were the main phyla in the compost.The main metabolic pathways were Amino Acid Metabolism,Carbohydrate Metabolism and Energy Metabolism.The PCA results showed that the microbial communities of the three groups were significantly different in the same period,indicating that the temperature affected the distribution of compost microbial communities.A total of 264 resistance genes were detected by high-throughput quantitative PCR,including 211 ARGs,44 Mobile Genetic Elements(MGEs)and 9 heavy metal resistance genes(MRGs).The number of ARGs,MGEs,and MRGs decreased in three groups during composting,and the reduction rates ranged from 4.00% to 24.67%,10.81% to 35.14%,and 33.33% to 55.56%.The reduction rate of gene number was the highest in the high-temperature group.At the end of composting,the sum of relative abundance of ARGs in three groups all decreased(reduced by 25.4%-34.0%),and the high-temperature group had the best reduction effect.The sum of relative abundance of MGEs in three groups also decreased significantly(decrease by 65.1%-66.0%),while the total of abundance of MRGs at the end of compost increased.The aerobic composting treatment had a better removal effect on vancomycin resistance genes,but had a poor removal effect on aminoglycosides,β-lactams,and MLSB resistance genes.High temperature can promote the reduction of some genes,such as aph3 via,bla-L1,cat B9,and erm(36).Spearman correlation analysis showed that the abundance of different types of resistance genes were significantly correlated with microbial community and physicochemical properties.ARGs were extremely significantly positively correlated with TOC,C/N,EC,MGEs,Spirochaetae and Cyanobacteria(0.473≤r≤0.779,p<0.01),and extremely significantly negatively correlated with temperature,Gemmatimonadetes,and Tenericutes(0.514≤|r|≤0.715,p<0.01).ARGs were positively correlated with Synergistetes(r = 0.462,p<0.05).MGEs were extremely significantly negatively correlated with temperature,p H,and Tenericutes(0.668≤|r|≤0.822),extremely positively correlated with EC and Cu(0.572≤r≤0.685),and significantly positively correlated with TOC,Actinobacteria,and Cyanobacteria.MRGs were significantly positively correlated with TP,Bacteroidetes,Spirochaetae,Chloroflexi and other phyla,and significantly negatively correlated with Zn,Firmicutes,and Proteobacteria,and significantly positively correlated with BRC1.