Effects of different graphene-based nanomaterials as elicitors on growth and ganoderic acid production by Ganoderma lucidum

Graphene-based nanomaterials (GBNs) have attracted considerable interest nowadays due to their wide range of applications. However, very little attention has been paid to the application of nanomaterials as potential elicitors for production of valuable metabolites. Herein, aiming to earn insight into effects of nanomaterials on secondary metabolite biosynthesis by medicinal fungi, we evaluated the influence of GBNs on growth and production of ganoderic acid (GA) by Ganoderma lucidum in submerged culture. Graphene oxide (GO), reduced graphene oxide (rGO), and rGO/Fe₃O₄ nanocomposite were synthesized successfully and characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy analysis. The prepared nanomaterials were added to the culture of G. lucidum at final concentrations of 50, 100, and 150 mg/L on Day 5. The results showed that the elicitation of G. lucidum with GO and rGO decreased the cell dry weight and GA production slightly, especially in higher concentrations. However, rGO/Fe₃O₄ nanocomposite not negatively affected cell growth and improved GA production. G. lucidum growth rate responded to elicitation experiments differently and depended on the type of nanomaterials and their concentrations, but almost all GBNs caused an increase in GA content (mg/100 mg dry weight). Also, field emission scanning electron microscopy morphological study showed that under elicitation, mycelia were more condensed and tightly stacked together. The findings from this study may suggest that GBNs in low concentrations could be applied as elicitors to secondary metabolites production from higher fungus, but further environmental, physiological, and biological studies required.