RESUMO
Serpula wood-decay fungi occupy a diverse range of natural and man-made ecological niches. Serpula himantioides is a forest-floor generalist with global coverage and strong antagonistic ability, while closely related species Serpula lacrymans contains specialist sister strains with widely differing ecologies. Serpula lacrymans var. shastensis is a forest-floor specialist in terms of resource preference and geographic coverage, while Serpula lacrymans var. lacrymans has successfully invaded the built environment and occupies a building-timber niche. To increase understanding of the cellular machinery required for niche adaptation, a detailed study of the P450 complement of these three strains was undertaken. Cytochrome P450 monooxygenases are present in all fungi and typically seen in high numbers in wood decay species, with putative roles in breakdown of plant extractives and lignocellulose metabolism. Investigating the genomes of these related yet ecologically diverse fungi revealed a high level of concordance in P450 complement, but with key differences in P450 family representation and expression during growth on wood, suggesting P450 proteins may play a role in niche adaptation. Gene expansion of certain key P450 families was noted, further supporting an important role for these proteins during wood decay. The generalist species S. himantioides was found to have the most P450 genes with the greatest family diversity and the highest number of P450 protein families expressed during wood decay.
RESUMO
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 Serpula himantioides, frequently found colonizing coniferous wood in nature. We report the morphological and chemical responses of S. himantioides to controlled intensities of UV-B 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 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 ß-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 responses of S. himantioides to controlled doses of UV-B radiation under in vitro culture conditions. We found that increased biosynthesis of xerocomic acid was the main strategy adopted by S. himantioides 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, 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 against UV radiation and should therefore be investigated in depth in the near future both in vitro and in vivo.