Exposure to UV-B 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 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.

Steroidal composition and cytotoxic activity from fruiting body of Cortinarius xiphidipus.

From the fruiting body of ectomycorrhizal fungi Cortinarius xiphidipus, sterols were identified from the crude extract and the cytotoxic effect of ergosta-4, 6, 8(14), 22-tetraen-3-one (ergone) was evaluated. Ten sterols including ergosta-3,5,7,9(11),22-pentaene, (22E)-ergosta-5,7,9(11),22-tetraen-3b-ol, (3ß,22E)-ergosta-5,7,22-trien-3-ol, (22E)-ergosta-7,22-dien-3-ol, neoergosterol, (3ß)-ergosta-5,8-dien-3-ol, (3ß)-ergosta-7-en-3-ol, stigmasterol, stigmasterol 22,23-dihydro and (22E)-ergosta-4,6,8(14),22-tetraen-3-one were identified from the crude extract. The cytotoxic activity of the sterol fraction containing ergosta-4, 6, 8(14), 22-tetraen-3-one was assessed on four tumour cell lines (Neuro-2a, Saos-2, MCF7 and LNCaP-C42). The cytotoxic activity against the four tumour cell lines tested, being Neuro-2a and Saos-2 the most sensitive, with a half-maximal inhibitory concentration (IC50) of 20.8 ± 2.2 and 27.8 ± 1.0 µg/mL, respectively. This is the first report of this Antarctic fungi collected in the Magallanes and Chilean Antarctica Region. This work represents a potential source for the development of anticancer drugs.

The best for the guest: high Andean nurse cushions of Azorella madreporica enhance arbuscular mycorrhizal status in associated plant species.

Positive interactions between cushion plant and associated plants species in the high Andes of central Chile should also include the effects of fungal root symbionts. We hypothesized that higher colonization by arbuscular mycorrhizal (AM) fungi exists in cushion-associated (nursling) plants compared with conspecific individuals growing on bare ground. We assessed the AM status of Andean plants at two sites at different altitudes (3,200 and 3,600 ma.s.l.) in 23 species, particularly in cushions of Azorella madreporica and five associated plants; additionally, AM fungal spores were retrieved from soil outside and beneath cushions. 18 of the 23 examined plant species presented diagnostic structures of arbuscular mycorrhiza; most of them were also colonized by dark-septate endophytes. Mycorrhization of A. madreporica cushions showed differences between both sites (68% and 32%, respectively). In the native species Hordeum comosum, Nastanthus agglomeratus, and Phacelia secunda associated to A. madreporica, mycorrhization was six times higher than in the same species growing dispersed on bare ground at 3,600 ma.s.l., but mycorrhiza development was less cushion dependent in the alien plants Cerastium arvense and Taraxacum officinale at both sites. The ratio of AM fungal spores beneath versus outside cushions was also 6:1. The common and abundant presence of AM in cushion communities at high altitudes emphasizes the importance of the fungal root symbionts in such situations where plant species benefit from the microclimatic conditions generated by the cushion and also from well-developed mycorrhizal networks.