Study On Secondary Metabolites And Biologicalactivities Of Fungus Aspergillus Ochraceus

The yield and quality of crops in today’s society have been improved with the advancement of science and technology,and the use of chemical pesticides has also increased.The imbalances of ecological environment and food safety have become the focus of people’s attention.The type of pollution-free green pesticide is an urgent problem to be solved.The starting point of this project is to obtain a well-developed strain and conduct large-scale fermentation to separate and purify its secondary metabolites to obtain monomeric compounds with good biological activity,which provides an excellent structural model for the development of new green pesticides and research ideas.In this paper,4 strains of different nutrients(RICE medium,PDB medium,MH1 medium,GPYM medium)were used to culture 8 strains of fungi derived from marine,soil and plants for optimization and cultivation.the fungus were screened from three aspects: productivity,the abundance of the metabolites and the antibacterial activity,it was found that the strain AAM-1 was excellent in all three aspects when fermented with RICE medium.Therefore,the strain AAM-1 was fermented by the superior RICE medium.According to the strain identification,the strain AAM-1 was Aspergillus ochraceus.The strain AAM-1 was fermented for 4 weeks with RICE medium,and the obtained metabolite was separated into a total of 18 components of Fr.1-Fr.18 by VLC gradient elution,and the crude extract was separated and purified by the activity tracking method.The antibacterial activity of 18 components was tested,and the biological activities of the components Fr.4,Fr.6 and Fr.8-Fr.16 were found to be good.Silica gel column chromatography,gel column chromatography and reversed phase column were used.Various modern chromatographic separation techniques such as chromatography and p TLC were further separated and purified,and more than 70 monomer compounds were obtained.The bioactive screening was carried out using two modes of filter paper and minimum inhibitory concentration.The antibacterial activity screening experimentand the nematode lethal experiment were carried out on 36 high quality samples.It was found that most of the monomeric compounds have better bacterial inhibition.Among them,L-4,L-27,L-28,L-41 and L-45 have broad-spectrum inhibition to bacteria,and the inhibition zone diameter of 6 strains is greater than 15mm;other antibacterial activities are stronger.The monomeric compounds are: L-69,which has strong selectivity to strain EC,the diameter of inhibition zone is 32mm(30 mm for positive control);L-74,which has strong selectivity to strain BT,the diameter of inhibition zone reaches 26mm(The positive control was 32 mm);L-48 had the strongest inhibitory effect on SA,and the inhibition zone diameter was 22 mm(36mm for the positive control);L-23 had the strongest inhibitory effect on XC,and the diameter of the inhibition zone reached 23 mm(The positive control was 35 mm);L-10 had the strongest inhibitory effect on BS,and the diameter of the inhibition zone reached 32 mm(36 mm for the positive control).In addition,the secondary metabolites of AAM-1 have a strong lethal effect on red nematodes,among which L-74,L-77 and L-68 have the strongest lethal toxicity to red nematodes,and the concentration of L-74 is 0.073 mg/ml.The red nematode can be killed in half within6 h.When the concentration is 0.150 mg/ml,the red nematode can die in half within4 h.When the concentration of L-77 is 0.095 mg/ml,the red nematode can die in half within 6h,the concentration is 0.157.At mg/ml,the red nematode can die in half within 4h;the LC50 value of L-68 at 8h is less than 0.1 mg/ml,and the toxicity is second.The concentration of 0.089 mg/ml can cause the red nematode to die in half within 8h.At 0.136 mg/ml,the red nematode can die in half within 6 hours.Considering the bacterial inhibition of monomeric compounds and the lethal toxicity of red nematode,L-7,L-10,L-69,L-74 and L-77 not only have strong antibacterial activity,but also have a strong lethal effect on Limnodrilus hoffmeisteri.L-7,L-10,L-69,L-74,L-77 are excellent in biological activity,and should be the key experimental object in subsequent experiments.