Migration And Transformation Of Antibiotic Resistance Gene And Heavy Metals In Compost-soil And Effect On Soil Microecology

With the growth of China’s population,the improvement of income and the improvement of people’s living standards,the livestock and poultry breeding industry is gradually developing to scale and intensification to meet people’s needs for meat products.A large number of antibiotics and heavy metals are used in livestock and poultry feed to prevent diseases and stimulate growth,resulting in the presence of heavy metals and antibiotic residues in livestock and poultry manure.Numerous studies have shown that antibiotics degrade easily,while heavy metals do not.At present,most of the researches on heavy metals are focused on their total amount,while the researches on biologically available heavy metals are few.The co-selective pressure of antibiotics and bioavailable heavy metals can lead to the production of antibiotic resistant strains and resistance genes（ARGs）in livestock manure.As an effective way to reduce antibiotics and antibiotic resistance genes and passivate heavy metals,composting has been widely used in the resource disposal and recycling of livestock and poultry manure.At present,there are few studies on the migration and transmission of antibiotics,heavy metals and ARGs between manure and compost during static composting and aerobic composting.Moreover,the study on the behavior change of soil microorganism and plant system after the land application of composting products is limited.In aerobic composting,microbial agents are often used to accelerate the compost.However,the effect of microbial agents on ARGs and heavy metals in the compost is not clear.Therefore,it is necessary to study the dynamic succession rules of antibiotics,heavy metals and ARGs pollution among manure,compost and soil during the standing and aerobic composting of livestock and poultry manure,and to further explore the effects on soil physical and chemical properties,soil enzyme and nitrogen cycling functional gene behavior.Aiming at the above problems,this research has achieved the following research results:（1）Study on the changes of antibiotics and ARGs in the process of static and aerobic composting.This study leave compost mainly choose different raw materials and the compost time of chicken manure composting（fresh chicken manure and wheat straw（CW）respectively,peanuts,straw（CP）,sawdust（CS）and corn biochar（CC））,and aerobic composting in choosing different raw chicken manure composting compost（fresh chicken manure respectively with life sludge,furfural,straw and biochar）at the same time,add the microbial agents for processing.We detected and quantitatively analyzed the changes of antibiotics,ARGs,and movable gene elements（MGEs）in the two stacking methods.The results showed that chicken manure was an important repository for antibiotics,ARGs and MGEs,and both stacks reduced or eliminated some types of ARGs in chicken manure.In the aerobic compost samples,the addition of microbial agents also had a certain influence on the change of ARGs abundance.Compared with other composting materials,both the absolute and relative abundance of ARGs in domestic sludge and chicken manure composting were higher than those in other composting combinations.（2）Distribution characteristics and risk assessment of total and speciation of heavy metals in stationary and aerobic compost.In this study,the content and speciation of heavy metals in static and aerobic compost samples were detected and quantitatively analyzed,and the passivation of heavy metals in compost by static compost,aerobic compost and enhancement of microbial agents was evaluated.The results showed that the content of As exceeded the national organic fertilizer pollution limit（15mg/Kg）,the content of Zn in most of the samples exceeded the limit（500mg/Kg）,the content of Pb in FP exceeded the limit（50mg/Kg）,the content of Cr in CC exceeded the limit（150mg/Kg）.The application of biochar increases the concentration of heavy metals in the compost.In the aerobic compost,the addition of bacteria had little effect on the total amount of heavy metals,and the copper（Cu）and chromium（Cr）in the aerobic compost samples all exceeded the national organic fertilizer limit standard.According to the risk assessment of the total amount of heavy metals in the aerobic compost samples,it was found that the pollution degree of nickel metal（Ni）in different test groups at the maturation stage: domestic sludge chicken manure compost + microbial agent（CSP4）,biochar chicken manure compost + microbial agent（CBSP4）and domestic sludge chicken manure compost（CS4）was level 1 light pollution.Copper（Cu）in all composting stages reached the pollution level,chromium（Cr）in most of the samples reached the pollution level,and the rest of the metals were at the non-pollution level.The risk assessment of heavy metal speciation before and after composting found that nickel（Ni）,except for furfural chicken manure composting grade,was of low risk grade.Metal zinc（Zn）was all in low risk and no risk levels.After copper（Cu）composting,the grade of furfural chicken manure composting changed from high risk to medium risk,and the risk grade of biochar chicken manure composting did not change before and after composting,which was still high risk grade.Metal chromium（Cr）is all in the low risk and no risk levels.Manganese metal（Mn）is all in the risk-free level.（3）Bacterial community composition and its correlation with heavy metals and ARGs in stationary and aerobic compost.In this study,16 S r RNA high-throughput sequencing technology was used to study the changes of microbial community during static composting and aerobic composting,and the relationship between them and antibiotics,heavy metals and ARGs was analyzed.The results showed that the bacterial communities in the static compost were mainly composed of Firmicutes,Proteobacteria,Bacteroidetes and Actinobacteria.The results of correlation analysis showed that As,Cu,Ag were positively correlated with various Args,and Hg,Cr,Cd were also positively correlated with the dominant phyla.Network analysis showed that the bacterial composition at the genus level was positively correlated with Args and Inti1.In aerobic compost,at the phylum level,it is mainly composed of Firmicutes,Actinobacteria,Proteobacteria,Bacteroidetes and Chloroflexi.Bioavailable copper（Bio-Cu）and bioavailable zinc（Bio-Zn）were positively correlated with ARGs.Cr,bioavailable copper（Bio-Cu）,bioavailable chromium（Bio-Cr）,Mn and Cu were positively correlated with the dominant phyla.Network analysis showed that did not use bacteria agent group,erm B,int I1,blac TX-M,oqx B has the most potential host bacteria,which was positively related with int I1 relationship of 23 species and 8 kinds of ARGs,bacterium agent in the treatment group,tet A,int I1,erm B,aac6’-Ib,has the most potential oqx B host bacteria,which was positively related with int I1 relationship with 22 species and 4 kinds of ARGs.Compared with the control group,it was found that the probiotics Bacillus in the control group was higher than that in the probiotics group,while the pathogenic bacterium Pseudomonas was lower than that in the control group.The application of microbial agents has a certain inhibitory effect on the killing of opportunistic pathogens,the reduction of ARGs and the transmission.（4）The application of chicken manure compost to Chinese cabbage planting and its effect on soil microecology.A 75 day pot experiment was conducted to study the effects of chicken manure compost application on the abundance and behavior of soil heavy metals,soil physicochemical properties,soil enzymes,ARGs and nitrogen cycling genes.The results showed that the changes of heavy metals in soil were not significant,but the activities of acid phosphatase,dehydrogenase and urease in rhizosphere soil were significantly increased.The absolute abundance of amo A,archa-amo A,nir K and nos Z genes in rhizosphere soil was significantly increased after the application of chicken manure composting.The absolute abundance of ARGs in the rhizosphere soil under different treatments was lower than that in the non-rhizosphere soil.Correlation analysis showed that there were significant positive and negative correlations between ARGs and different bacterial genera.The host number of ARGs in soil was significantly more than that in blank soil,and the host structure was significantly different from that in blank soil.It is suggested that bacterial community may play a key role in the succession of ARGs.