Effects Of OTC And SM₂ On The Diversity Of Microbial Community And Antibiotic Resistance Genes During Conposting

Antibiotics were used in livestock as veterinary medicines for therapeutic and sub therapeutic treatments and as growth promoting purpose. However, most of antibiotics were excreted through urine and feces. Thermophilic aerobic composting was an efficient way to utilizing the animal waste, and the residual antibiotics may had effects on the composting process. We conducted a thermophilic aerobic composting experiment of pig manure and wheat straw, with oxytetracycline(OTC) and sulfamethazine(SM2). Aimed to assess the effects on properties,enzymes activities, microbial community, degradation of OTC and SM2 and antibiotics resistance genes(ARGs),we had mainly used Biolog, T-RFLP, HPLC, q-PCR to complete this study. The research results were as follows:1. Effects of OTC and SM2 on properties and enzymes activities during compostingThe results showed that the temperature of the composting materials reached its peaks at about 55℃ and maintained for 4 days during composting process for all treatments, and the result of the seed germination experiment showed a germination index of above 85%,and the C/N was below 16,these results indicated the maturity of the composting materials in all the treatments. While antibiotics could delay the composting process in a short time.The dehydrogenase activity in H treatment(140 mg·kg-1 OTC + 30 mg·kg-1 SM2)was inhibited at the beginning of the composting process and then was promoted, while the urease activity showed a significant inhibitory effect in the cooling and mature period of composting. Antibiotics could inhibit the cellulase activity, significantly.2. Effects of OTC and SM2 on microbial communityThe results of the Biolog experiment showed that AWCD(Average Well Color Development), Shannon index and Simpson index of the high level antibiotics was significantly higher than those of control treatment in the mature period. Principal component analysis clearly revealed that the high level of antibiotics addition markedly changed microbial community structure during composting, the differentiation in utilization of carbon sources were mainly carbohydrates, polycarboxylic acids and amino acids.The results of the T-RFLP showed that the high level of antibiotics improved the bacterial community diversity but reduced the fungi community.Adding antibiotics may been induced resistant microorganisms. Cluster analysis showed that the bacterial and fungi community structure had been changed with the addition of antibiotics during composting. The high level of antibiotics changed the fungi community structure during the thermophilic period, significantly. Over all, the addition of antibiotics could change the microbial community, and had a greater influence on fungi community.3. Degradation of OTC and SM2 and the changes of antibiotic resistance genes(ARGs) during compostingThe residual rate of OTC was 2.8%、4.2%, respectively, in final products of L(140 mg·kg-1 OTC + 30 mg·kg-1 SM2)and H(140 mg·kg-1 OTC + 30 mg·kg-1 SM2)treatment, while SM2 content reduced below the detection limit. The degradation curve of antibiotics could be described by the first-order kinetic model with a half-life period ranged from 0.56 d to 1.24 d. Eight kinds of ARGs had been detected, including five resistance genes of tetracycline, two resistance genes of sulfonamide,one genes of class I integrons. Composting could remove almost all the SM2 and OTC, hence, thermophilic aerobic-composting is an effective process to eliminate antibiotics but were not good at eliminating ARGs, therefor more treatments were needed to reduce the risk before manure land application.