Isolation And Degradation Characteristic Of A New Sulfamethazine-degrading Bacterium

Sulfamethazine?SM2?is a frequently-used veterinary antibiotic.Because of its complex chemical structure,SM2 is difficult to be utilized by microorganisms.SM2 is frequently detected in the environment,which has become an emerging pollutant.The intermediates and degradation pathways of SM2 biodegradation are still unclear at present.In this study,an efficient sulfamethazine-degrading bacterium strain YL-1 was isolated from sulfamethazine-enriched activated sludge.The influencing factors and degradation kinetics of sulfamethazine degradation by strain YL-1 were explored.The degradation pathway of sulfamethazine by strain YL-1 was discussed.The biodegradation mechanism of sulfamethazine was investigated at the gene level,while the biological principle that YL-1 can tolerate high concentration of sulfamethazine was discussed.In this study,SM2 was used as the sole carbon source to domesticate the activated sludge.Through high-throughput sequencing technology,the change of the community structure of activated sludge was observed,and the abundance of Paenarthrobacter sp.was gradually increased during the domestication process.A highly efficient sulfamethazine-degrading bacterium was isolated from the domesticated activated sludge and named YL-1.By 16 S r RNA gene sequencing,strain YL-1 was identified as Paenarthrobacter ureafaciens.The optimal growth and degradation conditions for strain YL-1 were as follows: p H of 7.0,temperature of 30°C,rotation speed of 150 r/min and inoculation volume of 1.0%.Strain YL-1 had the capability to degrade several aromatic compounds including anthrone,sulfame-thoxazole,diphenylamine,sulfamerazine,carbazole,1-amino-2-naphthol-4-sulfonic acid and sulfadiazine.The growth kinetic model of strain YL-1 was constructed by Logistic equation.The maximum specific growth rate of strain YL-1 was 0.122 h-1.The biodegradation kinetics of sulfamethazine by the resting cells of strain YL-1 fitted well with the Haldane equation.The maximum specific degradation rate ?max was 0.523 h-1 and the half-saturation constant Ks was 89.83 mg/L.The intermediates from sulfamethazine biodegradation supernatant of strain YL-1 were identified by GC-MS/MS and LC-MS.A possible degradation pathway of sulfamethazine was proposed according to the intermediate identification and the concentration changes of TOC,NH4+ and SO42-during the SM2 biodegradation.SM2 was primarily hydrolyzed to produce 2-amino-4,6-dimethyl-aminopyrimidine and 4-amino-N-hydrobenzesulfonamide by the breakage of the S-N bond between sulfonic acid and amino.The strain YL-1 induced the formation of 4-amino-phenol from 4-amino-N-hydrobenzesulfonamide by stripping the sulfonic acid group.4-amino-phenol was finally mineralized to CO₂ and H₂O by strain YL-1,while 2-amino-4,6-dimethyl-aminopyrimidine could not be degraded by strain YL-1.The whole genome sequencing indicated that the strain YL-1 contained 5,071,183 bp and 6 plasmids.The GC content of strain YL-1 was 63.32% and the number of coding genes was 5,041.Compared with the KEGG PATHWAY database,the genome of strain YL-1 contained 18 genes coding the aromatic compound degrading enzymes and 89 genes related to xenobiotic degradation and metabolism.The strain YL-1 had 136 antibiotic efflux pump genes among antibiotic resistance genes.Plasmid A and Plasmid B carried a sulfonamide antibiotic resistance gene named sul1,respectively.It was supposed that the resistance gene in the genome enables strain YL-1 to tolerate high concentration of the sulfamethazine.