Isolation,Identification,Degradation Characteristics And Degradation Genes Of Napropamide Degrading Strain QC-18

Napropamide N,N-diethyl-2-(1-naphthalenyloxy)propanamide belongs to the amide herbicide family,which is one of the most commonly used pre-emergence herbicide for vegetables and crops to control annual gramineous weeds and some dicotyledonous weeds,uch as Echinochloa crusgalli(L.)Beauv.,Digitaria sanguinalis(L.)Scop.,Avena fatua L.,Setaria viridis(L.)Beauv.,Euphorbialathyris L.,Chenopodium album L.,Stellaria media(L.),Portulaca oleracea L.Wide-scale use of amide herbicids like napropamide resulting in pesticide residues in soil.he half-life of the degradation of napropamide is up to 70 days,so that its effect can be as long as one year.When pesticides are applied to soil,they may interact with non-target soil microorganisms,have a chronic adverse effect on soil health,and result in bioaccumulation in ecosystems.It may even hurt animal and human bodys though food chain.Due to its relatively high water solubility,it may also infect groundwater and surface water.To date,there are few reports on microbial degradation of napropamide.Isolation of some microbes can only degrade ?-naphthol and propanamide.And the degradation genes of napropamide have never been reported yet.In this work,a microbe strain Sphingopyxis sp.QC-18 which degraded napropamide was isolated from a napropamide-contaminated soil by the conventional enrichment culture technique.Sphingopyxis sp.QC-18 is an aerobic gram-negative bacteria with yellow,elliptical,and non-flagellum appearance.Its optimal growing conditions include 0-1.5%NaCl,neutral pH,and proper temperature in 30?.Sphingopyxis sp.QC-18 grows better in glucose than other carbon source.shows that 5%inoculation of Sphingopyxis sp.QC-18 is able to degrade more than 80%of 30 mg·L-1 napropamide at 30? within 72 hours.At pH 7.0,8.0 the degradation rate reached 80%.When the initial pesticide concentration was 25 mg·L-1,50 mg·L-1,the degradation rate of the strain QC-18 was the best,and the degradation rate was more than 90%.The results of liquid chromatography-mass spectrometry(LC-MS)analysis indicates that the molecular ion peak of the napropamide degradation product is 288.16 was presumed that a hydroxyl group was added to the benzene ring of the napropamide(peaking in 272.16)via Chem Draw software analysis.Toxicity experiments show that hydroxylated napropamide can reduce the biotoxicity of napropamide to a certain extent,but it can significantly reduce the inhibitory effect of napropamide on the germination of maize,and also suggest that hydroxylation of napropamide can reduce herbicidal activity.In the mutant insertion experiment,a mutant library of Spingopyxis sp.QC-18 was established by transposon mutation method.A mutant strain QC-18-M1 with loss of napropamide degradation ability was selected from 1200 mutants.The upstream and downstream sequences of the Tn5 transposon insertion site in the mutant strain QC-18-M1 were amplified by SEFA-PCR.In contrast to the genomic sequence of QC-18,it is predicted that the insertion of the inactivated nahQ gene is related to the addition of hydroxyl groups of napropamide.