Exposure to UV-B Radiation Leads to Increased Deposition of Cell Wall-Associated Xerocomic Acid in Cultures of .

Many fungi are thought to have developed morphological and physiological adaptations to cope with exposure to UV-B radiation, but in most species, such responses and their protective effects have not been explored. Here, we study the adaptive response to UV-B radiation in the widespread, saprotrophic fungus , frequently found colonizing coniferous wood in nature. We report the morphological and chemical responses of to controlled intensities of UV-B radiation, under culture conditions. Ultraviolet radiation induced a decrease in the growth rate of but did not cause gross morphological changes. Instead, we observed accumulation of pigments near the cell wall with increasing intensities of UV-B radiation. Nuclear magnetic resonance (NMR) and high-performance liquid chromatography-mass spectrometry (HPLC-MS) analyses revealed that xerocomic acid was the main pigment present, both before and after UV-B exposure, increasing from 7 mg/liter to 15 mg/liter after exposure. We show that xerocomic acid is a photoprotective metabolite with strong antioxidant abilities, as evidenced by DPPH (2,2-diphenyl-1-picrylhydrazyl), ABTS [2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt], and oxygen radical absorbance capacity (ORAC) assays. Finally, we assessed the capacity of xerocomic acid as a photoprotective agent on HEK293 cells and observed better photoprotective properties than those of β-carotene. Xerocomic acid is therefore a promising natural product for development as a UV-protective ingredient in cosmetic and pharmaceutical products. Our study shows the morphological and chemical responses of to controlled doses of UV-B radiation under culture conditions. We found that increased biosynthesis of xerocomic acid was the main strategy adopted by against UV-B radiation. Xerocomic acid showed strong antioxidant and photoprotective abilities, which has not previously been reported. Our results indicate that upon UV-B exposure, 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 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 against UV radiation and should therefore be investigated in depth in the near future both and .