## 3 Results
### Bioactive Metabolites
#### 3.5.3 Selenoamino Acids  
HPLC-ICP-MS was used to detect the selenoamino acids in _G. lucidum_ and the chromatograms were shown in Supplementary Figure S2. Three peaks with the same retention times as those observed for SeCys\({}_{2}\), MeSeCys, and SeMet standards were obtained in _G. lucidum_ cultured with 50 ppm and 200 ppm Na\({}_{2}\)SeO\({}_{3}\). As two main Se-conjugated amino acids, a higher proportion of SeMet than SeCys\({}_{2}\) was measured in the enzyme-hydrolyzed _G. lucidum_ mycelia extract. The contents of SeCys\({}_{2}\), SeMet, and MeSeCys all increased in the liquid culture process in _G. lucidum_ supplemented with 50 ppm Na\({}_{2}\)SeO\({}_{3}\), achieving the maximum values of 92.01, 445.83, and 54.44 mg/kg, respectively. In _G. lucidum_ supplied with 200 ppm Na\({}_{2}\)SeO\({}_{3}\), the SeCys\({}_{2}\) and SeMet content reached a maximum of 237.84 and 301.78 mg/kg, respectively, on the 4 th day during the culture process, which was followed by a decrease, MeSeCys showed a dramatic increase, being the highest on the 6 th day with 304.04 mg/kg. The MeSeCys content was five folds higher than that of _G. lucidum_ with 50 ppm Na\({}_{2}\)SeO\({}_{3}\). The Se proportion of the three selenoamino acids accounted for 55.72% of the total Se content in the 50 ppm Na\({}_{2}\)SeO\({}_{3}\) group, but the proportion was only 19.21% on the 4 th day and then decreased greatly in the 200 ppm Na\({}_{2}\)SeO\({}_{3}\) group (Table 2). Consequently, a low Se dose was optimal for selenoamino acid production during the entire process, and SeMet was the major component for _G. lucidum_. However, with a high Se content, the selenoamino acid proportions were profoundly changed. SeMet, and SeCys\({}_{2}\) decreased, while as the product of SeCys methylation, MeSeCys increased in this process and was the main component on the 6 th day. Hence, _G. lucidum_ was able to take up Na\({}_{2}\)SeO\({}_{3}\) directly and transformed it into organic Se. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multicolumn{2}{c}{**Bioactive Metabolites**} & \multicolumn{1}{c}{**Day 4**} & \multicolumn{1}{c}{**Day 5**} & \multicolumn{1}{c}{**Day 6**} \\ \hline \multirow{3}{*}{Polysaccharide (mg/L)} & 0 ppm & 269.81 \(\pm\) 16.81 \({}^{\text{a}}\) & 560.12 \(\pm\) 14.67 \({}^{\text{b}}\) & 1253.42 \(\pm\) 9.72 \({}^{\text{b}}\) \\ \cline{2-5}  & 50 ppm & 331.21 \(\pm\) 3.89 \({}^{\text{b}}\) & 702.81 \(\pm\) 25.68 \({}^{\text{c}}\) & 1365.97 \(\pm\) 10.93 \({}^{\text{c}}\) \\ \cline{2-5}  & 200 ppm & 262.23 \(\pm\) 8.06 \({}^{\text{a}}\) & 340.93 \(\pm\) 28.81 \({}^{\text{a}}\) & 259.11 \(\pm\) 32.86 \({}^{\text{a}}\) \\ \hline \multirow{3}{*}{Se(total) (mg/kg)} & 0 ppm & 2.92 \(\pm\) 0.65 \({}^{\text{a}}\) & 3.31 \(\pm\) 0.89 \({}^{\text{a}}\) & 2.86 \(\pm\) 0.23 \({}^{\text{a}}\) \\ \cline{2-5}  & 50 ppm & 275.11 \(\pm\) 27.39 \({}^{\text{b}}\) & 316.87 \(\pm\) 30.45 \({}^{\text{a}}\) & 421.69 \(\pm\) 29.07 \({}^{\text{a}}\) \\ \cline{2-5}  & 200 ppm & 1398.41 \(\pm\) & 22,472.65 \(\pm\) & 41,574.27 \(\pm\) \\  & 126.96\({}^{\text{c}}\) & 1271.83 \({}^{\text{b}}\) & 1933.50 \({}^{\text{b}}\) \\ \hline SeCys\({}_{2}\) (mg/kg) & \multirow{3}{*}{50 ppm} & 55.37 \(\pm\) 0.39 \({}^{\text{a}}\) & 82.85 \(\pm\) 4.52 \({}^{\text{a}}\) & 92.01 \(\pm\) 3.22 \({}^{\text{a}}\) \\ \cline{2-5}  & & 146.55 \(\pm\) 7.47 \({}^{\text{a}}\) & 243.96 \(\pm\) 9.31 \({}^{\text{a}}\) & 445.83 \(\pm\) 30.95 \({}^{\text{a}}\) \\ \hline MeSeCys (mg/kg) & \multirow{3}{*}{39.99 \(\pm\) 0.42 \({}^{\text{a}}\)} & 40.69 \(\pm\) 0.57 \({}^{\text{a}}\) & 54.44 \(\pm\) 1.25 \({}^{\text{a}}\) \\ \cline{2-5}  & & 237.84 \(\pm\) 13.22 \({}^{\text{b}}\) & 177.23 \(\pm\) 12.21 \({}^{\text{b}}\) & 160.99 \(\pm\) 14.51 \({}^{\text{b}}\) \\ \cline{2-5}  & & 301.78.