Colorful fungi and their Pigments.
(Photos: Fly Agaric, Cortinarius, Cantharellus, Ganoderma)
Ever wondered how some of the fungi, especially the visible mushrooms possess characteristic brilliant colors? Yes they produce a wide variety of compounds like quinones, carotenoids, betacyanins, alkaloids, xanthones , biphenyls, melanin etc. The interested reader may refer (Jan and Karrel, 2011). Various pigments and other fungi constituents show important biological activities like antioxidative, free radical scavenging, anticarcinogenic, immunomodulatory, antiviral and antibacterial that have generated intensive research interest.
The important groups of pigments of fungi are as follows.
1. Quinones.
Most of us are familiar with the ubiquitous plastoquinones, ubiquinones and tocopherols and vitamin K. But Quinones, the aromatic diketones, form the largest class of natural colouring matters and of the total 800 and more compounds known, about 50% occur in higher plants and of the rest, a large percentage are known form fungi. Fungi like Aspergillus, Fusarium, Penicillum, Monascus, Trichoderma, and Laetiporus are reported to produce simple quinones, anthraquinones, Rubropuntamine, Rubropuntatin, Ankaflavin, Monascin, β-carotene, and many other pigments responsible for various colors, viz. red, purple, yellow, brown, orange, and green.
Cortinarius the largest genus of agarics, (1000spp.), Dermocybe and Tricholoma contain a range of anthraquinones like fallacinol, bright yellow dimeric anthraquinone, flavomannin-6,6 ́-di-O-methyl ether, green (3R)-atrochrysone seen in C. atrovirens and C. odoratus .
Gomphidius and Suillus of the order Boletales are characterized by a diversity of colours that are mainly derived from terphenylquinones like polyporic acid and the yellow pulvinic acids. Pulvinic acids are especially widespread in mushrooms belonging to the Gomphidiaceae and Suillaceae families,
Prenylated benzoquinones, like meroterpenoids such as boviquinones are seen in genera like Chroogogompus and Suillus
2. Carotenoids
Carotenoids are not widespread in higher fungi as they are in plants; nevertheless, they have been isolated from several yellow pigmented Cantharellus species. The golden chanterelle, C. cibarius pigment mixture was found to consist mainly of β-carotene and also present were lycopene, α-carotene and two other carotenes, probably the γ- and δ-isomers or the xanthophyl canthaxanthin that was found in the pink to red-orange cinnabar chanterelle C. cinnabarinus as the main pigment
Scaurins are the polyene pigments with bound glutamic acid that were isolated from the fruiting bodies of C. Scaurus.
Orange-yellow polyenes of fatty acid origin, dihydroxerulin, xerulin and xerulinic acid (27), are the pigments of Oudemansiella that act as inhibitors of cholesterol biosynthesis.
3. Betacyanins in Fly Agaric (Amanita)
The striking orange-red pigments of the cap of fly agaric, Amanita muscaria are a mixture of the purple betacyanin muscapurpurin , orange betaxanthins muscaurins and yellow muscaflavin
4. Xanthones in Cortinarius
Cortinarius contain the xanthone dermoxanthone and its methyl ester which are responsible for the bright yellow fluorescence under UV light (Gill 1999).
5. Alkaloids in Cortinarius
Canthin-6-one alkaloids are produced by some other Cortinarius. species. The parent compound canthin-6-one (21) occurs in the bitter-tasting C. infractus (Pers.) Fr. together with the β-carboline derivatives infractin A and B (22) (Gill 1996). The benzotropolone derivative aurantricholone (23), isolated from the bright orange-red caps of Tricholoma aurantium.
The pyrroloquinone alkaloids isolated from Mycena include red mycearubin A (29), mycearubin B (30) and related compounds from the fruiting bodies of M. rosea
Hydrazine derivatives. The carrot truffle, Stephanospora caroticolor contains in its subterranean tuber-like fruiting bodies the pigment stephanosporin occuring naturally as its potassium salts and is responsible for the bright orange colour of the mushroom (LANG et al. 2001).
6. Styryl pyrones
The yellow-brown styrylpyrone pigments bisnoryangonin and hispidin (25) are widespread among fungi of the Strophariaceae familie, genera Gymnopilus, Hypholoma and Pholiota. It also occurs in mushrooms of the Hymenochaetaceae family, e.g. in Inonotus
7. Biphenyls
In genus Suillus, biphenyls derived from 1,2,4-trihydroxybenzene include the red gomphilactone (43) and the corresponding . Variegatorubin (44) and xerocomorubin are the coloring pigments.
8. Melanin like pigments
3,4-Dihydroxyphenylalanine melanins from Ganoderma luteum.
A note on medicinal values of some mush rooms.
Some of them are not edible and are toxic if ingested. But many of them are now considered medicines of high therapeutic value. For.e.g. Fly Agaric is used as a treatment for sore throats, and arthritis, and as an analgesic. Its tincture helps to relieve sciatica and other pain, including joint pain and swollen lymph nodes. Tincture can also be applied to external infections, for example nail fungus, and skin conditions found in Lyme disease. Cortinarius collinitus is mentioned in this US patent on dietary supplements to improve immune function, treat malignancies and virus infection. Cantharellus cibarius has been reported to display a wide variety of biological properties, including antimicrobial, cytotoxicity, antioxidant, antihypoxic, antihyperglycemic, wound healing, anti-inflammatory, iron-chelation activity. Ganoderma increases body resistance against the growth of tumors, induce the production of interferon, enhance the immunity function, and kill tumor cells within the body.
References:
Jan V. And Karel C (2011) Pigments of higher fungi: a review, Czech Journal of Food Sciences 29(2):87-102
Mammen Daniel
