Effects Of Process Parameters On Antibiotic Resistance Gene Abundance And Microbial Community Structure During Anaerobic Digestion Of Cow Manure

Anaerobic digestion can reduce the antibiotic resistance genes(ARGs)in the feces of livestock and poultry,and help to reduce the environmental pollution and ecological risk.In order to know the influence of process parameters on the ARGs abundance and microbial community structure in the anaerobic digestion system of cow manure,the anaerobic digestion experiments were carried out under three process parameters of temperature,stirring and solid content.The physic-chemical features of anaerobic digestion,ARGs abundance,mobile genetic elements(MGEs)abundance and microbial community structure were analyzed,and the the relationships between physic-chemical characteristics,ARGs,MGEs and microbial community structure were explored,and the key factors affecting the ARGs abundance under different process parameters during anaerobic digestion were revealed.The main results and conclusions are as follows:(1)The thermophilic anaerobic digestion can shorten the reaction time for 15 days compared with mesophilic anaerobic digestion,the total biogas production and methane production increased by 13.92% and 16.86;the concentration of SCOD increased by 47.49%,and the concentration of TAN decreased by 5.64%;the absolute abundance of ARGs decreased 0.75 log;the abundance of Bacteroides and Spirochetes was decreased,and the abundance of Firmicutes was increased to 86.58%.(2)During the mesophilic anaerobic digestion,stirring increased total biogas production and methane production by 12.63% and 6.00%,SCOD concentration by 26.39%,TAN concentration by 3.91%;ARGs absolute abundance by 0.13 log;the abundance of Spirochete decreased from 15.42% to 2.66%,and Bacteroides increased from 40.26% to 52.49%.During the thermophilic anaerobic digestion,stirring had no significant effect on total biogas production,total methane production and ARGs abundance,but decreased MGEs abundance by 0.18 log;the abundance of Chloroflexi decreased from 5.43% to 3.15%,and that of Firmicutes increased from 86.58% to 91.96%.(3)When the solid content increased from 4% to 16%,the total biogas and methane production of anaerobic digestion increased from 4463 mL and 1987 mL to 6637 mL and 3602 mL,and the concentration of SCOD increased from 3158 mg/L to 5575 mg/L;the absolute abundances of ARGs decreased from 0.70 log to 0.06 log,and the absolute abundances of MGEs decreased from 0.62 log to 0.23 log;the potential hosts of ARGs are Bacteroides,Firmicutes and Spirochetas.With the increase of solid content,the abundance of Bacteroides decreased from 49.70% to 38.17%,and that of Spirochetes increased from 9.37% to 28.69%.(4)RDA analysis showed that physic-chemical features,MGEs and microbial community could explain more than 99.8% of ARGs changes.Bacteroides,Firmicutes and Proteobacteria were positively correlated with tet O,tet T,tetQ and tetX,they are potential host bacteria of ARGs.Spirochetes were positively correlated with tet A,tetC and tetG;and they were potential host bacteria of ARGs.Thermophilic anaerobic digestion decreased the abundance of Proteobacteria,Bacteroides and Spirochetes,so it promoted the removal of ARGs;strring increased the abundance of Bacteroides,therefore the absolute abundance of tetA,tet C,tetG and Tn916/1545 decreased by 0.22~0.73 log,and decreased the abundance of Spirochetes,therefore the absolute abundance of tetQ,tetX,intI1 and intI2 increased by 0.18~2.24 logs.High solid content decreased the removal of the abundance of Bacteroides and Firmicutes,increased the abundance of Spirochetes,and promoted the removal of tetA,tetG,tet Q,tetT,tetX,int I1 and Tn916/1545.