Exposure to UVB radiation leads to increased deposition of cell-wall associated xerocomic acid in cultures of Serpula himantioides

Many fungi are thought to have developed morphological and physiological adaptations to cope with exposure to UVB radiation, but in most species such responses and their protective effects have not been explored. Here, we study the adaptive response to UVB radiation in the widespread, saprotrophic fungus Serpula himantioides , frequently found colonizing coniferous wood in nature. We report the morphological and chemical response of S. himantioides to controlled intensities of UVB radiation, under in vitro culture conditions. Ultraviolet radiation induced a decrease in the growth rate of S. himantioides , but did not cause gross morphological changes. Instead, we observed accumulation of pigments near the cell wall with increasing dosage of UVB radiation. NMR and HPLC-MS analysis revealed that xerocomic acid was the main pigment present, both before and after UVB exposure, increasing from 7mg/L to 15mg/L after exposure. We show that xerocomic acid is a photoprotective metabolite with strong antioxidant abilitites, as evidenced by DPPH, ABTS and ORAC assays. Finally, we assessed the capacity of xerocomic acid as a photoprotective agent on HEK293 cells and observed better photoprotective properties than β-carotene. Xerocomic acid is therefore a promising natural product for development as a UV-protective ingredient in cosmetic and pharmaceutical products. Importance Our study shows the morphological and chemical response of S. himantioides to controlled doses of UVB radiation under in vitro culture conditions. We found that increased biosynthesis of xerocomic acid was the main strategy adopted by S. himantioides against UVB radiation. Xerocomic acid showed strong antioxidant and photoprotective abilities, which has not previously been reported. Our results indicate that upon UVB exposure, S. himantioides decreases its hyphal growth rate and uses this energy instead to increase the biosynthesis of xerocomic acid, which is allocated near the cell wall. This metabolic switch likely allows xerocomic acid to efficiently defend S. himantioides from UV radiation through its antioxidant and photoprotective properties. The findings further suggest that xerocomic acid is a promising candidate for development as a cosmetic ingredient to protect from UV radiation and should therefore be investigated in depth in the near future both in vitro and in vivo .