Isolation And Identification Of Secondary Metabolites From Xenorhabdus Ehlersii SN22

Entomopathogenic bacteria can produce a large number of low molecular weight toxins that are especially active either antibacterial or insecticidal active substances.More scholars focus on the research of Xenorhabdus.spp.Xenorhabdus.spp played a significant role in new sources of biopesticides.In resent years,the study of Xenarhabdus.spp mainly focus on the fermented liquid activity and insecticidal mechanism research rather than isolation identification and biological activity of the secondary metabolites study in our country.This article focus on the research of Xenorhabdus.spp.Mainly include:molecular biology identification,separation and purification of secondary metabolites in the small molecule monomer compounds,identification of small molecules of chemical structure and determination of small molecules of antibacterial activity.The main conclusions are as follows:1.Identification of SN22 strain:16SrDNA gene sequence similarity and phylogentic analysis indicated that the strain of antimicrobial activity obtained from soil belonged to the genus Xenorhabdus ehlersii DSM 16337T/AJ810294 and named Xenorhabdus ehlersii SN22.2.Separation and Purification of Secondary Metabolites of SN22:Xenorhabic acid(compound 1)was isolated from fermented broth of X.ehlersii SN22 by silica gel column chromatography and Sephadex LH-20 chromatography.Characterized by X-ray crystal diffraction,1HNMR and 13C NMR,and ESI-MS spectral analysis,the chemical structure of 1 was confirmed to be 3-(cyclohex-2-en)acrylic acid which was a new natural product.Compound 2,Compound 3,Compound 4 and Compound 5 are known compounds,identified as Xenorhabdins 4,Xenorhabdins 5,Xenorhabdins 2 and Xenorhabdins 1,respectively.3.The antifungal activity of Xenorhabic acid against phytopathogenic fungi was determined by mycelium growth rate method.The results showed Xenorhabic acid could effectively inhibit the mycelium growth of Sclerotinia sclerotiorum and Pythium aphanidermatum,and the EC50 values were 27.99 and 29.55 μg/mL respectively.In addition,Xenorhabic acid also showed antibacterial activity against Escherichia coli,with the minimum inhibitory concentration(MIC)value of 62.5 μg/mL.The activity of the dithiopyrrolone compounds(compound 2,compound 3,compound 4 and compound 5)against pathogenic bacteria was determined by the microdilution method.The results showed that the minimum inhibitory concentration(MIC)activity of Xenorhabdins 4 to Bacillus subtilis and Staphylococcus aureus was only 4 μg/mL and 2 μg/mL.The activity of Xenorhabdins 5 to Bacillus subtilis is preferably 32 μg/mL.Xenorhabdins 2 had the best inhibitory activity against Bacillus subtilis,with a minimum inhibitory concentration of 2μg/mL,followed by Staphylococcus aureus at a minimum inhibitory concentration of 32μg/mL;Xenorhabdins 1 had the best activity against Staphylococcus aureus,The minimum inhibitory concentration was 16 μg/mL.The dibenzopyrrolone compounds found in this paper did not show good bioactivity to Streptococcus uberis,Xenorhabdins 4 and Xenorhabdins 2 concentrations of 256 μg/mL had a weak activity against Streptococcus triticus.