Study On The Change Of ARGs In Composting Of Livestock And Poultry Manure

Antibiotic resistance genes(ARGs)is an emerging environmental pollutant.Due to the frequent use of antibiotics in livestock breeding process,resulting in a group of Antibiotic-resistant bacteria(ARBs)in the intestines of livestock,these ARBs carrying large amounts of ARGs,they may enter the environment through feces.Now,compost is the most commonly used livestock manure treatment technology,composting can reduce manure volume,and kills harmful bacteria.In this study,we used modern molecular biological technology:qualitative PCR,fluorescent quantitative PCR and 16S rDNA high-throughput sequencing,the changes of tet-R and ARBs,and the correlation between ARGs and ARBs in composting process were analyzed.The fresh fecal samples were collected from a pig farm and a chicken farm in Shanghai,and the conclusions are as follows:(1)tet-R genes in pig manure samples(other than tet(D)is not detected)are detected,and this indicates that tet-R genes are commonly found in pig manure.According to the detection rates,the 10 kinds of tet-R genes detected positive ranked in order with tet(A)=tet(O)=tet(M)>tet(X)>tet(G)>tet(B)=tet(C)>tet(S)>tet(E).Until the end of the composting,tet(B),tet(C),tet(E),tet(G),tet(S)were not detected,but the tet(A),tet(M),tet(O),and tet(X)were still remained.tet-R genes in chicken manure samples(other than tet(D),tet(B),tet(E)is not detected)are detected,this indicates that tet-R genes are commonly found in chicken manure.According to the detection rates,the 10 kinds of tet-R genes detected positive ranked in order with tet(A)=tet(O)=tet(M)>tet(X)=tet(S)>tet(G)=tet(C).Until the end of the composting,tet(C)was not detected,but the tet(A),tet(S),tet(G),tet(M),tet(O)and tet(X)are still remained.Studies have shown that most of the tet-R genes in the compost are remained at the end,but a small part of the tet-R genes are completely removed,so composting has a certain effect on the elimination of ARGs.(2)The contents of tet(A)and tet(C)in composting of pig manure were lower compared with that of fresh pig manure,and decreased in the process of composting,and the removal were 49%and 99.9%respectively,suggesting that composting has a better effect on tet(C)removal.The correlation analysis showed that the content of tet(A)in pig manure compost was significantly correlated with the change of C/N(P<0.05)),negatively correlated with pH change(P<0.05),which suggested that C/N and pH were probably important factors in the reduction of ARGs during composting.The levels of tet(A)and tet(C)genes in chicken manure compost were also lower than those of fresh chicken manure,and with the composting of tet(A)and tet(C),removed 98.8%and 69.6%respectively.The treatment of chicken manure compost was more effective for the removal of tetr(A)than tet(C),which was different from the treatment of pig manure compost.The abundance of tet(C)was positively correlated with C/N(P<0.05),suggesting that C/N and pH may play important roles in the removal of ARGs.(3)High-throughput sequencing results show that the Firmicutes,Bacteroidetes,Actinobacteria and Proteobacteria are the dominant microflora in the composting process of pig manure and chicken manure,and most of ARBs belong to the four categories.The community structure of pig manure and chicken manure changes significantly after high temperature composting,and the study found that the bacteria related to ARGs in pig manure and chicken manure mainly include Bacteroides、Enterobacteriaceae、Pseudomonadaceae、Ruminococcus、Clostridium、Parabacteroides、Prevotellaceae、Pseudomonas、Corynebacterium、Ruminococcaceae,and these flora showed a decreasing trend after high temperature composting,furthermore,the relative abundance of some flora decreased significantly.Thermomonosporaceae、Streptosporangiaceae、Micromonosporaceae、Bacillaceae、Halanaerobiaceae、OPB54_norank、Paenibacillaceae、Alcaligenaceae、Methylococcaceae、Oceanospirillales_unclassified、Saprospiraceae、Clostridia unclassified、Firmicutes unclassified、Bacilli_unclassified、S0134_terrestrial_group,the abundance in fresh pig manure and fresh chicken manure is low,and even some bacteria does not exist in fresh pig manure and chicken manure,the bacteria abundance increased significantly after composting.