Effect Of Different Metal Ions On The Content Of Polysaccharide In Lentinus Edodes Mycelium And Study Of Its Mechanisms

With the changes in people’s living environment,living habits and living conditions,health problems are gradually increasing,especially the incidence of diseases such as cardiovascular and cerebrovascular diseases and malignant tumors is increasing year by year.Currently,there are no specific drugs for treating these diseases.It is of great significance to research and develop bioactive components of edible and medicinal fungi with various medicinal properties and few side effects.As a kind of edible and medicinal fungus,Lentinus edodes is the first cultivated fungus strain in East Asia and the second in the world.Its main metabolite,lentinan,has many aspects such as anti-tumor,immunity,anti-virus,anti-oxidation and blood sugar lowering.It is one of the most promising functional food and pharmaceutical resources.Therefore,it is of great value to increase the yield of lentinan.Metal elements are indispensable components of microbial growth and reproduction and normal metabolism,and can affect the synthesis of secondary metabolism of microorganisms.Polysaccharide metabolism is a complex biochemical process.Studying its specific mechanism can provide theoretical support for improving the yield of lentinan.In this experiment,the main cultivar mushroom variety Xin808 was used as the experimental material.Firstly,the mycelial biomass,intracellular polysaccharide and extracellular polysaccharide content of L.edodes were used as reference indicators to determine the optimum inducing concentration and optimal induction time of different metal ions.Then,the optimum metal ion concentration was added under the optimal induction time,and the samples were periodically sampled to analyze the dynamic process of the biomass and polysaccharide content of L.edodes mycelium.At the same time,the enzyme activities and transcriptional expression levels of key enzymes in L.edodes polysaccharide synthesis were analyzed.These results will help to clarify the effect of different metal ions on the content of lentinan and its mechanism.The main research contents and results are as follows:（1）There are large differences in the biomass,intracellular polysaccharide and extracellular polysaccharide content of L.edodes mycelium at different concentrations of five metal ions(Na⁺,K⁺,Ca²⁺,Mn²⁺,Fe²⁺),and the suitable concentration can promote L.edodes growth and secondary metabolism,increasing polysaccharide yield.The results of total polysaccharide content showed that the optimum concentration of the five metals was 600,1000,1000,600,200 mg/L,and the promotion was Fe²⁺>Mn²⁺>Na⁺>Ca²⁺>K⁺.（2）On the basis of the optimal concentration,metal ions were added in different time periods during the fermentation,and the mycelial biomass,intracellular polysaccharide and extracellular polysaccharide content were determined.According to the results of total polysaccharides,the optimal induction time of Na⁺,K⁺,Ca²⁺,Mn²⁺and Fe²⁺were at the time of inoculation,after 3 days of static culture,3 days of static culture and then 7 days of shaking,7 days of shaking and 10 days of static culture.（3）Metal ions were added at the optimal induction concentration and optimal induction time,and the dynamic changes of mycelium polysaccharides and biomass were analyzed.Different metal ions affect the growth of L.edodes mycelium at different times,in which Na⁺is in the late fermentation stage,Ca²⁺is in the middle of fermentation,Fe²⁺is in the early and late stages of fermentation,and Mn²⁺promotes the growth of mycelium in the whole fermentation process.Under the treatment of K⁺,Ca²⁺and Mn²⁺,the polysaccharide content reached the maximum at 60 d,which were44.49,54.51 and 55.42 mg,respectively.Fe²⁺and Na⁺reached a maximum at 45 d（54.92 mg）and 30 d（55.63 mg）,respectively.（4）Under optimal induction concentration and optimal induction time,activities of UGPase,PGM and PGI and their transcriptional expression levels changed greatly throughout the fermentation process.All five metal ions can affect UGPase,PGM and PGI activities,but the degree of influence and the process of occurrence are different.Correlation analysis with polysaccharide content showed that PGI enzyme activity was negatively correlated with intracellular polysaccharide content,and PGM and UGPase activity were positively correlated with intracellular polysaccharide content.There was no significant correlation between PGI enzyme activity and its transcriptional expression.PGM activity was significantly positively correlated with its transcriptional expression under Fe²⁺treatment,and not correlated under other metal ions treatments.UGPase activity was positively correlated with its transcriptional expression.