Microbial Degradation Mechanism Of Tetracycline Antibiotics

Oxytetracycline?OTC?is a widely used tetracycline antibiotic in the prevention and treatment of human and animal diseases.In recent years,the waste of containing OTC produced by OTC producing enterprises and animal husbandry has posed a threat to the environment and human health.Therefore,the contamination of OTC remains to be solved.However,the instability of OTC greatly increases the difficulty of physicochemical treatment of OTC pollutants.Compared with physicochemical treatment,microbial degradation method is simple and convenient,and can effectively avoid secondary pollution caused by chemical treatment.In this study,a highly efficient degradation strain was used to remove OTC from environmental media.On the one hand,degradation pathways and influencing factors of OTC in different environmental media were systematically studied;on the other hand,fluorescence quantitative method was used to conduct real-time monitoring of common tetracycline antibiotic resistance genes,so as to indicate the change trend of resistance genes in the process of OTC contamination.In addition,the changes of microbial community in the reaction system were studied.The specific results are as follows:?1?A strain of bacteria,T4,which can degrade oxytetracycline,was identified as Pseudomonas from the residue produced in the process of oxytetracycline production.By optimizing the degradation conditions,it was found that Fe³⁺played an important role in promoting microbial degradation of OTC.Established under the action of Fe³⁺,the substrate concentration of 50 mg L^-1,temperature of 40?and pH=7,the degradation of OTC rate can reach 80.96%.When applied to real water matrices,the OTC degradation percentages were 88.22%,91.55%and 91.97%in pond water,aquaculture wastewater and sewage,respectively.?2?In water matrice,the four common tetracycline antibiotic resistance genes tet?M?,tet?A?,tet?O?and tet?W?were detected real-time fluorescent quantitative PCR?qPCR?detection.The detection results showed that the presence of these four resistance genes was not detected in water.Since OTC hydrolysis is inevitable in aquatic media,the hydrolysis and microbial degradation pathways of degradation products are analyzed using UPLC-Q-TOF to deduce OTC products in the the water,mainly including enol-ketone conversion,hydroxylation,dehydration,deamination,demethylation and decarbonylation.?3?In the soil medium,the effects of soil type,substrate concentration and temperature on OTC products with external microbial degradation have been studied.The experimental results show that,in not sterilized soil,2.5 mg kg^-1,30?conditions,OTC removal effect is best,degradation rate can reach 68.53%.High-throughput sequencing technology was used to detect the changes of microbial communities in the soil,and the main dominant flora were proteobacteria,firmicutes,bacteroidetes,acidobacteria and bacillus.With the reaction time,proteobacteria,bacteroidetes,acidobacteria and bacillus all increased.Among them,the number of proteobacteria in the control group remained basically unchanged,and the increase was the largest in the experimental group,reaching 11.99%.Bacteroidetes,acidobacteria and bacillus were increased by 17.03%,6.53%and 4.16%,respectively,in the control group,and by 20.72%,9.45%and 5.83%,respectively,in the experimental group.Therefore,it is inferred that the added T4 bacteria degradation OTC may be related to proteobacteria,bacteroidetes,acidobacteria and bacillus in soil.In addition,the 13 tetracycline antibiotic resistance genes tet?A??tet?B??tet?C??tet?G??tet?H??tet?K??tet?L??tet?M??tet?O??tet?Q??tet?W??tet?X?and tet?Z?were detected during the reaction.On day 0,tet?X?was detected in both treatments,and the content in the experimental groups was higher than that in the control groups.With the extension of response time,tet?G?,tet?M?,tet?Q?and tet?Z?are gradually detected in two groups of experiments and the number of them is increasing.The experimental groups have the highest content of tet?G?.