Study On Secondary Metabolites And Biological Activities Of Marine Source Fungus Aspergillus Flavus

The problem of pesticide pollution with higher exposure frequency brings great trouble and inconvenience to human production and life.Therefore,it is one of the important directions for pesticide research and development to choose environmentally friendly pesticides with good efficacy,degradable,low pollution and low side effects.In this paper,the marine endophytic fungi were isolated and purified by the abundant marine resources in Qingdao,and the vigorous AF strain(Aspergillus flavus)was fermented on the scale,and the secondary metabolites were separated and purified by activity tracking technology.First,three strains of different sources were cultured using four different media of GPYM,RICE,MH1 and PDB,and strains were screened by comparing the weight,species and biological activity of the metabolites.The screening results showed that in the amount of secondary metabolites,the amount of metabolites was the largest in RICE medium,followed by MH1,and the other two media showed a general metabolic amount.In terms of the richness of metabolites,it was found that the AF strains were rich in metabolites in RICE medium and CF strain in MH1 medium after spot chromatography.Through the inhibition test of the three strains of metabolites on the bacteria of four common crops,it was found that the activity of secondary metabolites produced by AF strain in RICE medium was the most prominent.The maximum inhibition zone of EC was 28mm(positive diameter was 30mm).For BT,the largest inhibition zone is 24mm(positive diameter 32mm).The AF strain was identified by molecular biological means as Aspergillus flavus.AF strains were fermented in large scale in RICE medium,and gradient elution was performed using VLC to obtain 12 crude samples with different polarities,and the agricultural antibacterial activity screening test was carried out.The 12 crude samples were screened for agricultural antibacterial activity,and the results showed that Fr.3~Fr.7 had better activity.Among them,Fr.5 had the most significant inhibitory effect on BS,BT and XC.The diameter of the inhibition zone reached 24 mm,21mm and 23mm(positive control: 27 mm,27mm,32 mm respectively).The 12 crude sample fractions were subjected to repeated separation and purification using column separation,and finally 23 monomer compounds were obtained.In the screening process of monomeric antibacterial activity,it was found that AF17 and AF20 had stronger antibacterial activity: the inhibition zone diameter of AF17 to BS and BT was 22 mm(positive control was 30 mm)and 18 mm(positive control was 30 mm).The inhibition zone diameter of AF20 for BS,EC,and SA was 25 mm(30 mm for positive control),18 mm(26 mm for positive control),and 20 mm(30 mm for positive control).In addition,AF8 and AF18 exhibited specific antibacterial effects on XC with diameters of 21 mm and 18 mm,respectively(32 mm for the positive control).AF21 and AF22 have only a certain antibacterial activity against SA,and the diameter of the inhibition zone is 15 mm(30 mm for the positive control).It is speculated from the above analysis that AF17 and AF20 have good antibacterial activity and have potential and value for further research.