Preliminary Study On The Isolation And Activity Of Oosporins In The Fungus Of The Genus Acresporium

Fungi are rich sources of natural products with various bioactivities,and fungal secondary metabolites have attracted considerable attention because of their biological properties,which may lead to new agricultural and medicinal applications.Three strains of the genus Acremonium,CA022,AJ013 and YX015,were isolated from the fruiting bodies of Shiraia bambusicola.It has been confirmed that the extracts of liquid and solid-state fermentations of these strains have different degrees of antioxidant activity and strains of the genus Acremonium can produce metabolites such as terpenes,glycosides and peptides.Therefore,in this study,the solid-state fermentations of the three strains were studied in order to obtain natural products with biological activity.In this study,the fungal strain Acremonium cavaraeanum CA022 was cultured in solid-substrate fermentation cultures to prepare the crude extract.Then,the crude extract was isolated and purified by silica gel column chromatography,polyamide column chromatography and recrystallization to afford orange red crystals,which were identified as 3,3',6,6'-tetrahydroxy-4,4'-dimethyl-1,1 '-bi-p-benzoquin-one,i.e.oosporein,using a combination of IR,1D-,2D-NMR and single-crystal X-ray diffraction.It was found that strains AJ013 and YX015 were also capable of metabolizing oosporein by TLC and HPLC fingerprint analysis.The concentrations of oosporein in the solid fermentation cultures of strains CA022,AJ013 and YX015 measured by a HPLC standard curve method were 6.44(EtOAc),9.39(MeOH)and 9.44 mg/g(MeOH),respectively.In addition,the peak areas of oosporein in the EtOAc and MeOH extracts of the strain YX015 and EtOAc extract of the strain AJ013 were all more than 90%.Antioxidant activities of oosporein were investigated by the methods of?-carotene bleaching,1,1-diphenyl-2-picrylbydrazy(DPPH),pyrogallol autoxidation and sulfosalicylic acid.The results show that inhibition effect of oosporein on the?-carotene/linoleic acid assay system was slightly lower than that of VE.The radical scavenging activity towards DPPH was as strong as VE and its IC50 value was 64.26?g/mL.The superoxide anion radical scavenging activity was remarkably stronger than VE.The scavenging effect of oosporein on hydroxyl radical was lower than VE in the concentration range of 20-50 ?g/mL,but stronger than VE when the concentration reached 60 ?g/mL.Therefore,oosporein is antioxidant metabolite of strains CA022,AJ013 and YX015.In addition,oosporein alao exhibited a certain nematode activity against Bursaphelenchus xylophilus with LC50 values of 957.82?g/mL at 36 h and 475.74 ?g/mL at 60 h.In this study,we reported oosporein isolated from A.cavaraeanum for the first time and speculated that Acremonium fungi will generally produce oosporein.AJ013 and YX015 are two high-yield strains of oosporein.In addition,the results may serve as clues to explore the relationships between these fungi and their host S.bambusicola.