Bioactivity Of Secondary Metabolites From Freshwater Fermentation Of A Marine Fungus

Since the 20th century,food shortage caused by population growth has been a major problem plaguing social development.In order to reduce the harm of diseases and insects and improve food output,chemical synthesis of organochlorine pesticides,organophosphorus pesticides,DDT and other large-scale applications in agricultural production and life.The excessive use of chemical pesticides is not only toxic,but also will exist in the environment for a long time,which is difficult to degrade in the natural environment.With the passage of time,ecological environmental problems caused by chemical pesticides gradually appear.Through bioenrichment and food chain transmission,it will eventually endanger human beings.In order to protect human health and sustainable development of ecological environment,many countries begin to eliminate these highly toxic and difficult to degrade chemical pesticides.Therefore,it is a priority to develop new low-toxicity and easily degradable pesticides.Due to the novel structure and good biological activity of natural products,researchers of new pesticides focus on natural products,among which fungal secondary metabolites with high activity and low harm are an important direction of Marine resources development.In this paper,through the isolation and purification of invivo fungi collected from plants and animals in Laoshan Seaarea of Qingdao,three strains of fungi were obtained,namely AF,HTF and HYA.After the analysis of productivity and metabolite richness of the three strains,afaspergillus flavus was finally selected as the target strain for large-scale fermentation culture.After gradientelution of fermentation products by vacuum column chromatography,26 crude components were obtained.Fr6-Fr12 was identified as the crude component with excellent activity by antibacterial,algal,red nematode and halozoan activities.Then,the Fr6-Fr12 was separated and purified by silica gel column and gel column repeatedly,and finally 17 monomers were obtained.The bioactivity of single substance was screened by antibacterial activity and halogenated insect activity.The results showed that AFDS-9,AFDS-13 and AFDS-14 had strong antibacterial activity.Afds-14 had the strongest antibacterial activity against Escherichia coli,and the diameter of antibacterial zone was 18 mm（positive control was 27 mm）.AFDS-9had the strongest inhibitory activity against Bacillus thuringiensis and Pseudomonas aeruginosa,and the diameters of the inhibition zones were 14 mm and 15 mm（25 mm and 28 mm for positive control）,respectively.AFDS-13 and AFDS-14 showed strong inhibitory activities against Staphylococcus aureus,Bacillus subtilis and Escherichia coli.It was found that AFDS-9,AFDS-11 and AFDS13-17 had strong inhibitory effect on halogenia at low concentration.The mortality rate of halogenia wasmore than 80%when cultured at 5μg/m L for 16 h.The isolated and purified components showed strong inhibitory activity against halogenia,among which AFDS-13,AFDS-14,AFDS-16 and AFDS-17 showed strong inhibitory activityagainst halogenia,with LC₅₀ values of11.119,10.119,6.254 and 8.708μg/m L respectively.Combined with the experimental analysis of bacteriostatic activity and halogen insect activity,AFDS-9,AFDS-13 and AFDS-14 not only had excellent bacteriostatic activity but also showed excellent halogen insect inhibitory activity.It could be inferred that these three monomers had excellent biological activity,and their structure-activity relationship could be further studied based on the molecular structure characteristics.