Biosynthesis of Eudesmane-type Sesquiterpenoids by The Wood-rotting Fungus, Polyporus brumalis, on Specific Medium, including Inorganic Magnesium Source

Fungi, such as the wood-rotting Polyporus brumalis, are excellent sources of pharmaceutically interesting natural products such as sesquiterpenoids. In this study, we investigated the biosynthesis of P. brumalis sesquiterpenoids on modified medium. Ten additional species of white rot fungi were inoculated in medium containing nutrients such as $C_6H_{12}O_6$, $C_4H_{12}N_2O_6$, $KH_2PO_4$, $MgSO_4$, and $CaCl_2$ at $28^{\circ}C$ for 25 days. After 10 days of incubation, eudesmane-type sesquiterpenes, ${\beta}$-eudesmane and ${\beta}$-eudesmol, were only synthesized during the growth phase of P. brumalis. Experiments excluding one nutrient at a time were conducted to determine the effects of inorganic nutrients on sesquiterpene biosynthesis. In conclusion, GC-MS analysis showed that biosynthesis of sesquiterpenes was differentially regulated by inorganic nutrients such as $MgSO_4$, $C_4H_{12}N_2O_6$, and $KH_2PO_4$. We found $MgSO_4$ supplementation to be vital for eudesmane-type sesquiterpene biosynthesis in P. brumalis; nitrogen ($C_4H_{12}N_2O_6$) and phosphate ($KH_2PO_4$) inhibited the synthesis of P. brumalis metabolites. Magnesium is a known cofactor of sesquiterpene synthase, which promotes ${\beta}$-eudesmol synthesis. To mechanistically understand eudesmane-type sesquiterpene biosynthesis in P. brumalis, further research into the genes regulating the dynamics of such biosynthesis is warranted.