Screening And Degradation Characteristics Of Sulfamethazine And Its Intermediate Degrading Strain

Sulfamethazine(SM2),as the most used sulfamethazine antibiotic,is not easy to be absorbed and metabolized,which will cause serious negative effects on human health and ecological environment.At present,the mineralization rate of SM2 by single strain is low,the intermediates produced by degradation can cause secondary pollution degradation pathways and interactions between bacteria are not clear.Therefore,by enriching and domesticating the degrading bacteria in biogas slurry,this paper explored the degradation characteristics of SM2 degrading bacteria,speculated the biodegradation pathway and refractory intermediates,and analyzed the diversity and composition of the community.In addition,SM2-degrading bacteria M7 and refractory intermediate-degrading bacteria Z4 were screened from the enrichment liquid.The degradation characteristics of single strain and co-culture were studied respectively,and the following conclusions were drawn:(1)Through enrichment and domestication of biogas slurry,it was found that the degradation rate and mineralization rate of SM2 were100% and 48.68% respectively.The flora consisted of 8 phyla and 18 genera among which Proteobacteria,Actinomycetes and Firmicutes were the dominant phyla,and Hyphomicrobium sp.and Paracoccus sp.were the dominant genera.A total of 17 products were produced in the metabolic process and 3 degradation pathways were formed by mass spectrometry analysis.The difficult degradation intermediates of2-amino-4,6-dimethylpyrimidine(SM2-AP)were speculated and verified.(2)SM2-degrading bacteria M7 and SM2-AP degrading bacteria Z4 were screened from enrichment solution.The Hyphomicrobium sp.M7 was a gram-negative bacterium and could fully degrade SM2 with a mineralization rate of 26.34%.The degradation process was in line with first-order decay kinetics.Five products were identified in the metabolic process,and two degradation pathways were found.The conversion rate of SM2 was 50%.SM2-AP degrading bacteria Z4 was a gram-positive bacterium,belonging to Dietzia sp.,and the degradation rate of SM2-AP could reach 100%,and the mineralization rate was 71.28%.The degradation process also followed first-order decay kinetics.(3)The degradation characteristics of the co-culture(M7,Z4)showed that the mineralization rate of SM2 was up to 35.13% when the inoculation ratio of M7:Z4 was 2:1,and the mineralization rate of the co-culture was 10% higher than that of the single strain.Meanwhile,the degradation rate of SM2 and SM2-AP increased by 2.80 times and 3.30 times respectively.Comprehensive analysis showed that during the degradation process of SM2,M7 degraded SM2 and SM2 converted to SM2-AP,providing carbon source for Z4,and finally completing the mineralization of SM2 through further degradation of Z4 metabolism.The study showed that the cooperation between bacteria was the key to improve the mineralization rate.