Isolation Of Nicosulfuron-degrading Strains And Analysis Of The Degradation Mechanism

In the present study,nicosulfuron-degrading bacteria were isolated from a continuous stress-cultivated microbial consortium LAMC3 using high-throughput sequencing technology combined with culturomics.A total of five nicosulfuron-degrading strains were obtained,of which the strain LAM1902 was a novel species,and another novel species(strain LAM9072)also was isolated without the degradation ability.The results of polyphasic taxonomy indicated that the strain LAM9072 represented a novel species of the genus Photobacterium,for which the name Photobacterium salinisoli sp.nov.was proposed,and results showed that the novel strain LAM9072 had no degradation effect on nicosulfuron.On the other hand,the results also showed strain LAM 1902 was a novel species of the genus Pseudomonas,for which the name Pseudomonas nicosulfuronedens sp.nov.was proposed.When nicosulfuron was provided at an initial concentration of 50 mg/L,strain LAM 1902 could degrade 90.7%of the nicosulfuron,LAM 1902 showed the great application potential.Therefore,the research on the degradation characteristics and mechanism of nicosulfuron-degrading strain LAM1902 were investigated in detail.Firstly,the optimal degradation conditions of nicosulfuron-degrading strain LAM 1902 were investigated and optimized by single-factor analysis,the optimal degradation conditions for nicosulfuron degradation by LAM1902 were found to be 30℃,pH 6,0,and the inoculum biomass at 5.0%(v/v).At the same time,it was found that the strain LAM 1902 could tolerate and degrade the concentration of 500 mg/L nicosulfuron,and it also has the degradation efficiency of 66.5%on 50 mg/L ethersulfuron and can degrade chlorsulfuron-methyl of 50 mg/L completely.Secondly,total of seven intermediate metabolites of nicosulfuron degradation were detected by liquid chromatography and mass spectrometry,containg the 2-(N-carbamoylsulfamoyl)-N,N-dimethylnicotinamide,2-amino-4,6-dimethoxypyrimidine and series of metabolites.Furthermore,the multiomics(genomics,transcriptomics,metabolomics)were used to further research the mechanism of strain LAM 1902 in response to nicosulfuron exposure.The results showed that the genome of strain LAM1902 was 6.68 Mbp including 141 contigs.Under the stress of nicosulfuron,total 859 up-regulated genes and 527 down-regulated genes were detected,most of which were differentially expressed genes were enriched to the "ABC transporters" pathway.Finally,according to the results of metabolomics,a model of nicosulfuron biodegradation by LAM1902 was proposed,it seems likely that in order to eliminate the stress of nicosulfuron,LAM 1902 produced some metabolites,such as myo-inositol,trehalose and 3-aminoisobutanoic acid,as part of an overall mechanism of self-protection.Based on these findings.This study is the first time to report metabolomics studies of nicosulfuron-degrading bacteria,which lays the foundation for the research on the degradation of nicosulfuron and also provides new idea for the degradation of other environmental pollutants.