Polyketides Produced By Streptomyces Sp. SA61 And Their Insecticidal Activity Against Myzus Persicae

The green peach aphid（Myzus persicae）is a globally distributed agricultural pest which is detrimental to more than 500 plant species and cause severe economic losses.Chemical insecticides are the main means to control M.persicae,but the frequently and unregulated use of chemical insecticides has led to the development of resistance and increased the difficulty of controlling M.persicae.In response,the research and development of efficient,low toxicity,and environmentally friendly new biological insecticides has become a research hotspot in pest control.Natural products are one of the important sources of new pesticide discovery.Actinomycetes play an important role in discovering novel Natural products.In order to seek natural products with novel structures and virulence activity against M.persicae,107 strains of actinomycetes were cultivated by shaking,and the crude extracts were screened for detection of thin layer chromatography and stomach toxicity activity against M.persicae.Based on the two screening results,Streptomyces sp.SA61 was selected as the targ strain to study the inhibiting activity against M.persicae.Secondary metabolites of Streptomyces sp.SA61 were separated and purified to obtain monomer compounds.The nuclear magnetic resonance spectroscopy,and X-ray single crystal diffraction were analyzed to determine their chemical structures including the absolute configurations.Insecticidal activity of stringmycin A-F against M.persicae,effect of the active compound stringmycin A on activity of the detoxification enzymes in M.persicae and its safety evaluation the on crops were determined.The specific research results are as follows:1.Screening of target strains:107 strains of actinomycetes were cultured in two kinds of culture medium by shaking flask to obtain 214 crude extracts.According to the results of thin layer chromatography,33 crude extracts with rich metabolites were selected,and their stomach toxicity activities against M.persicae were detected by feeding method.Based on the results of thin layer chromatography and insecticidal activity screening,Streptomyces sp.SA61 was finally selected and its active components were studied.2.Shaking culture of Streptomyces sp.SA61 and isolation and purification of crude extract:Streptomyces sp.SA61 was subjected to culture in a shaking table at a temperature of 28℃and a rotational speed of 180 r/min for 7 days,with a total of 48 L.Solid phase extraction was performed using macroporous adsorption resin and eluted with organic solvents to obtain 20 g of crude extract.Six pure compounds were isolated from the secondary metabolites of Streptomyces sp.SA61 by silica gel column chromatography,gel column chromatography and HPLC.3.Identification of secondary metabolites of Streptomyces sp.SA61:by analyzing data of high-resolution mass spectrometry（HRESIMS）,¹H NMR,¹³C NMR,2D-NMR and X-ray single crystal diffraction,the chemical structure of compounds 1-6 were derived as polyketides.By comparing with literature data,the results indicated that compound 1 was previously isolated in our laboratory;compounds 2-6 were novel compounds with different carbon skeletons from 1.Compounds 1-6 were named as strekingmycin A-F.4.Determination of insecticidal activity of strekingmycin A-F against M.persicae:the toxicity against M.persicae was determined by leaf soaking method,and the results showed that strekingmycin A-F had insecticidal activity against M.persicae,with LC₅₀ of 10.29,14.57,27.81,34.47,31.57,and 21.04μg/m L at 96 h,respectively.The stomach toxicity activity against M.persicaes was determined by feeding method,and the results showed that strekingmycin A-F had stomach toxicity activity against M.persicaes,with LC₅₀ of 12.04,15.61,16.63,17.20,12.48,and 23.50μg/m L at 96 h,respectively.The contact toxicity activity against M.persicaes was determined by tube membrane method,and the results showed that strekingmycin A-F had contact toxicity activity against M.persicaes,with LC₅₀of 11.58,13.30,11.97,13.68,12.80 and 24.57μg/m L at 96 h,respectively.The antifeedant activity against the M.persicae was determined by honeydew method,and the results showed that strekingmycin A-F had antifeedant activity against the M.persicae,with AC₅₀ of 10.41,13.09,10.86,12.56,10.52,and 10.86μg/m L at 96 h,respectively.The repellent activity against M.persicaes was determined by leaf plate method,and the results showed that strekingmycin A-F had repellent activity against M.persicaes.After 48 h,the repellent rates were 82.67%,82.31%,73.33%,62.30%,54.88%and 69.87%,respectively.The results showed that strekingmycin A has the best insecticidal effect.5.The effect of the active compound stringmycin A on the activity of detoxification enzymes in M.persicaes:the results showed that stringmycin A inhibited the detoxification enzymes in M.persicaes,including cytochrome P450（CYP450）,carboxylesterase（Car E）and glutathione-S-transferase（GST）,which reduced their detoxification ability,and made stringmycin A more toxic to M.persicaes.6.Safety evaluation of strekingmycin A on crops:the effects of strekingmycin A at 100μg/m L on the germination,emergence,and growth period of tomatoes and peppers were measured.The results showed that there were no significant differences in germination rate,plant height,root length,leaf color,and development degree between all treatment groups and the control group,indicating that strekingmycin A had no effect on tomatoes and peppers at 100μg/m L.The above experimental results indicated that the polyketides produced by Streptomyces sp.SA61,strekingmycin A-F,not only have structural novelty,but also have insecticidal activity M.persicae.Strekingmycin A can inhibit the detoxification enzymes activity,and reduce the detoxification ability of M.persicae which showed the potential to become a lead compound of the insecticide.