Ganoderma lingzhi is one of the important edible and medicinal fungi with broad pharmacological activities, such as anti-tumor, immunity improvement and anti- oxidation, and also rich in selenium. Selenium is an essential trace element. Selenium-deficiency can cause diseases such as Keshan disease and thyroid disease. Selenium from organic sources was more bioavailable and less toxic than inorganic selenium. Due to the limitations of selenium production in plants and animals, microorganisms have become an important source of selenium in the commercial scale. G. lingzhi can convert inorganic selenium into organic selenium effectively. Therefore, G. lingzhi can be explored as a new source of organic selenium.
By supplying sodium selenite in culture media, we investigated the effects of exogenous selenium selenite on the contents of selenium, polysaccharide and triterpenoids in G. lingzhi in different periods after inoculation. High performance liquid chromatography (HPLC) was applied to compare the similarity of triterpenoids in different periods and to measure the content of ganoderic adid A, E and F. Quantitative real-time polymerase chain reaction (qRT-PCR) was used to detect the expression of key enzyme gene involved in triterpenoid biosynthesis.
The results showed that sodium selenite supply effectively improved the selenium content in G. lingzhi. Selenium content (57.8 μg/kg) was the highest in G. lingzhi at 50 days after inoculation, which was 34.42% higher than the control. Organic selenium content was 35.95% higher in fruiting bodies supplied with 50 mg/kg sodium selenite than that of the control. Sodium selenite supply also enhanced the content of polysaccharide in fruiting bodies at 40-70 days after inoculation. Fruiting bodies at 60 days after inoculation had the highest content of polysaccharide (13.24 mg/g), which was 53.95% higher than that of the control. Sodium selenite supply decreased the content of triterpenoids in different periods after inoculation. We found that the spectra of triterpenoids in fruiting bodies at different bag opening time shared about 98% similarity, indicating that the compositions of triterpenoids in fruiting bodies from different periods after inoculation were similar. Sodium selenite supply significantly decreased the contents of ganoderic acid A, E and F in fruiting bodies. qRT-PCR analysis showed sodium selenite supply significantly decreased the expression of 3-hydroxy-3-methylglutarylcoenzyme A (HMGR) gene in fruiting bodies.
To conclude, sodium selenite supply effectively improved the contents of selenium and polysaccharides in G. lingzhi, but reduced the contents of triterpenoids and ganoderic acids. However, the compositions of ganoderic acids were not altered by sodium selenite supply.