Study On Antifungal And Antioxidant Properties Of Fungal Secondary Metabolites

In recent years,the incidence of invasive fungal infections has increased clinically,duing to the long-term use of antibacterial,anti-tumor and immune-suppressant drugs,diseases such as AIDS,diabetes and cancer,the extensive development of interventional,organ or bone marrow transplantation and the aging population,the number of people with low immune function increased.Invasive fungal infections are mainly caused by pathogenic fungi such as Candida spp.,Aspergillus spp.and Cryptococcus spp..When these pathogenic fungi invade the immune-compromised population,they proliferate in the tissues,organs and blood system of patients and lead to serious inflammatory reaction,tissue damage and even death.At present,the antifungal drugs used in clinic include azoles,echinocandins,pyrimidines and polyenes.Because there are few kinds of antifungal drugs and the side effects are serious,the drug resistance of common pathogenic fungi in clinic is becoming more and more serious,which leads to difficult treatment,poor prognosis and high mortality.It is an urgent problem to develop safe and effective antifungal drugs.Natural products are rich in sources,various in types,novel in structure and wide in pharmacological effects.They are important sources of new drug development.Many compounds with pharmacological properties have been isolated from various natural products from plants,such as berberine,cinnamaldehyde and jatrorrhizine with antifungal property,ginsenosides,ginkgolides and rutin with antioxidant property,artemisinin with antimalarial property,paclitaxel with anticancer property,tanshinone for treating cardiovascular diseases,etc.Endophytes in plants and microorganisms in their root soil can produce metabolites similar to the host structure and biological property,which can replace plants as a huge treasure house for screening natural property products and new drug lead compounds.In this study,260 fungi and 57 bacteria were isolated from soil and plant samp-les.There are 13 genera of fungi identified,of which Aspergillus spp.and Alternaria spp.have the highest isolation rate.3 isolates of fungi have good antifungal and anti-oxidant properties.Paramyrothecium roridum M3-1 has the certain inhibitory effect on common clinical pathogenic fungi and has a high scavenging rate for free radica-ls that can cause oxidative damage.The incubated conditions were optimized according to the property and dry we-ight of metabolites of isolate M3-1.The most suitable incubated conditions are pota-to dextrose agar,p H 5.5,culture for 8 days,shaking table speed of 180r/min and me-dium volume of 150m L.The metabolite of isolate M3-1 was isolated and purified by extracting with ethyl acetate,Silica gel column chromatography,and recrystallization.Component M3-1-c has the best propertiy,the MIC₅₀of Candida albicans,Candida krusei and Candida parapsilosis is 4μg/m L,the MIC₅₀of Cryptococcus neoformans was 16μg/m L,and the MIC₅₀of Aspergillus fumigatus was 32μg/m L,and the clearance rates of DPPH radical,O₂^ˉradical and OH radical were 88.9%,73.7%and 75.2%respectively.Through the analysis of gas chromatography-mass spectrometry,it is speculated that this component is benzoic acid derivatives.Analyzing antifungal mechanism of functional component M3-1-c against Candida albicans,increasd of concentration,the hydrophobicity of cell surface decreases,the gene expression levels of glucan synthase and chitin synthase decreased,the biosynthesis of glucan and chitin in cell wall decreased.Under this functional component,the cell wall structure was destroyed,and the exposure of dextran and chitin increased.When the concentration of this component is high,it will also change the permeability of cell membrane and cause damage to it.To sum up,the isolate of Paramyrothecium roridum was obtained in this study and the functional components of its metabolites have good inhibitory effects on common Candida spp.such as Candida albicans,Cryptococcus neoformans,and Aspergillus fumigatus,and have strong antioxidant capacity;after separation,purification,and identification,it is speculated that the component is the benzoic acid derivative;Candida albicans was selected as the research object to explore the antifungal mechanism of this functional component,found that it can inhibit the gro-wth and proliferation of pathogenic fungi by reducing cell hydrophobicity,inhibiting the biosynthesis of major components of cell walls,and destroying cell walls.The results of this study can provide some experimental basis for the development of new antifungal drugs.