Molecular Identification Of Endophytic Fungus HJG3 And Preliminary Study On Its Secondary Metabolites

ObjectiveIn this study,the taxonomic status of the endophytic fungus HJG3 isolated from Polygonatum sibiricum was determined by molecular identification,of which the antioxidant activities of the fermentation extract and mycelium extract crudes were tested and the secondary metabolites were isolated,purified and identified.This study aims to find novel secondary metabolites,which is expected to provide alternative compounds for the research and development of new drugs.MethodsThe rDNA ITS sequence was applied for the taxonomy of the endophytic fungus HJG3.The antioxidant activity of this fungus liquid fermentation was tested by potassium ferricyanide reduction method and DPPH radical scavenging rate method.The secondary metabolites of the fungus HJG3 were isolated and purified by Thin-Layer Chromatography,silica gel column chromatography（CC）,and high performance liquid chromatography（HPLC）et al,of which the structure of the compounds was identified by ¹H NMR,¹³C NMR.ResultsCompared with Gen Bank data,the endophytic fungus HJG3 was identified as Nectriaceae sp..Within the scope of 0.5～2.5 mg/ml of HJG3 fermentation liquid extract,the scavenging rate of DPPH free radical increased with the increase of concentration,which presented a good dose-effect relationship,and its IC₅₀ value is 0.3397 mg/ml,a little larger than that of BHT（0.0703 mg/ml）and V_C（0.0518 mg/ml）.In the range of 0.5～4mg/ml of HJG3 mycelium extract,the scavenging rate of DPPH free radical increased with the increase of concentration,which also showed a good dose-effect relationship,and its IC₅₀ value is 4.9824 mg/ml,obviously higher than that of BHT（0.0703 mg/ml）and V_C（0.0518 mg/ml）.In the determination of reducing power,within the scope of 0.0625～4mg/ml of HJG3 fermentation liquid extract,the absorbance value increased with the increase of concentration,and the EC₅₀ value 1.1771 mg/ml,a little larger than that of BHT（0.1034 mg/ml）and V_C（0.0796 mg/ml）.In the range of 0.0625～2 mg/ml of HJG3mycelium extract,the absorbance value also increased with the increase of concentration,its EC₅₀ value 4.4719 mg/ml,obviously higher than that of BHT（0.1034 mg/ml）and V_C（0.0796 mg/ml）.Six compounds were isolated from the secondary metabolites of the fungus HJG3.These compounds include:p-hydroxybenzoic acid,p-methylbenzoic acid et al,in which the compounds1,2,5,6 are presumed to be new compounds andrequire further study.ConclusionThe endophytic fungus HJG3 belongs to Nectriaceae,of which the liquid fermentation has good antioxidation activity.This study frist reported the secondary metabolites of Polygonatum sibiricum.Six compounds of Chromogenic ketones and phenolic acids were isolated from the fungus HJG3.Therefore,the fungus HJG3 is a potential resource for screening natural bioactive components,and this sdudy provides a theoretical basis for the exploitation of the endophytic fungi from Polygonatum sibiricum.