Metabolic Response of Sanghuangporus baumii to Zn2+ Induction and Biosynthesis of a Key Pharmacological Component: Triterpenoid

Triterpenoids derived from <i>Sanghuangporus baumii</i> exhibit potent antitumor activity, but their yields under natural conditions are relatively low due to their status as secondary metabolites. In this study, we investigated the effects of Zn²⁺ induction on the growth and triterpenoid biosynthesis of <i>S. baumii</i>. The results showed that 0.5 mM Zn²⁺ significantly enhanced the mycelial growth rate (0.43 ± 0.004 cm/d) and biomass (4.8 ± 0.024 g/L), representing increases of 8.71% and 16.95%, respectively, compared with the Zn0 group. This result was mainly caused by an increase in the soluble sugar content. Furthermore, 5 mM Zn²⁺ induced upregulation of genes in the mevalonate (MVA) pathway, thereby promoting triterpenoid accumulation by 167.86% compared with the Zn0 group. Transcriptome analysis identified <i>SbHMGS</i> as the key gene involved in triterpenoid biosynthesis under Zn²⁺ induction. Heterologous expression of <i>SbHMGS</i> in <i>Saccharomyces cerevisiae</i> confirmed its critical role in triterpenoid production. The triterpenoid (squalene) content of the engineered strain (<i>Sc</i>-<i>HMGS</i>) reached 0.88 mg/g under Zn²⁺ induction, which was 208.6% higher than in the non-induced control strain (<i>Sc</i>-NTC). These findings provide a foundation for optimizing the industrial fermentation condition of <i>S. baumii</i> and <i>S. cerevisiae</i> to enhance triterpenoid yields.