Screening And Degradation Characteristics Of A Tetracycline-degrading Bacterial Strain

Antibiotics are one of the largest and most widely used drugs in the world.Among them,tetracyclines are one of the most commonly used antibiotics because of their low cost and convenient use,especially in livestock and poultry breeding.However,tetracyclines can not be completely absorbed by animals,most of them are discharged in the form of active form?parent compound or metabolite?with feces and urine.The residue of tetracycline in the environment is bound to have a profound impact on the ecological environment.So there is a serious problem that how to remove antibiotics in the wastewater.At present,the treatment methods of tetracycline and other antibiotics wastewater can be divided into physical-chemical methods and biological methods.Biological treatment is a method of treating antibiotic residues by microorganisms,and it has become a research hotspot now because of its advantages of low cost and strong specificity,and will not cause secondary pollution.In this study,the effective biodegradation bacteria of tetracycline were screened from activated sludge,and the degradation characteristics and optimal degradation conditions were studied through single factor test and response surface method.Finally,the related tetracycline resistance genes were further explored.The results of the research are as follows:Three tetracycline degrading strains were screened from activated sludge,and the degradation effect of strain TTC-1 was the most significant.TTC-1 was identified as a klebsiella pneumonia according to the observation of colonial morphology,Gram staining and 16S rRNA homology analysis.The effect of the temperature,starting pH of medium,inoculation amount and type of metallic salt on the degradation of tetracycline by klebsiella pneumonia TTC-1 were studied,the results showed that the optimum temperature of klebsiella pneumonia TTC-1 is 30?,and the best pH is 7.Manganese ions can promote the degradation of tetracycline by TTC-1,and its optimal dosage is 0.4 g/L.On the basis of single factor test,the method of response surface analysis was adopted to optimize the degradation condition.As a result,the optimum conditions for tetracycline degradation by klebsiella pneumonia TTC-1 were as follows:temperature 34.4?,pH 7.22,MnSO₄ concentration 0.32 g/L.Under the optimal conditions,the degradation rate of tetracycline based on model prediction is 93.77%,and the verification value is 94.26%,which indicates that the established model has high accuracy.The resistance genes tet?D?,tet?E?,tet?M?,tet?O?and tet?X?were successfully cloned from strain TTC-1.Among which,tet?D?and tet?E?are efflux pump genes,tet?M?and tet?O?are ribosome protective genes,and tet?X?is an enzyme modifying gene.This study indicates that klebsiella pneumonia TTC-1 has good degradation effect on tetracycline,which is expected to provide a reference for bioaugmentation treatment of tetracycline containing wastewater.