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

## TL;DR

This study shows that adding zinc improves the growth and production of triterpenoids in a mushroom species, which could help make more of these valuable antitumor compounds.

## Contribution

The study identifies Zn²⁺ as a key inducer of triterpenoid biosynthesis and highlights SbHMGS as a critical gene in this process.

## Key findings

- Zn²⁺ at 0.5 mM increased mycelial growth and biomass of S. baumii.
- 5 mM Zn²⁺ upregulated MVA pathway genes, boosting triterpenoid accumulation by 167.86%.
- Heterologous expression of SbHMGS in S. cerevisiae increased squalene production by 208.6% under Zn²⁺ induction.

## Abstract

Triterpenoids derived from Sanghuangporus baumii 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 S. baumii. 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 SbHMGS as the key gene involved in triterpenoid biosynthesis under Zn²⁺ induction. Heterologous expression of SbHMGS in Saccharomyces cerevisiae confirmed its critical role in triterpenoid production. The triterpenoid (squalene) content of the engineered strain (Sc-HMGS) reached 0.88 mg/g under Zn²⁺ induction, which was 208.6% higher than in the non-induced control strain (Sc-NTC). These findings provide a foundation for optimizing the industrial fermentation condition of S. baumii and S. cerevisiae to enhance triterpenoid yields.