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Fungi Pigments

The fruit bodies and spores of many fungi contain colour pigments - why? 

Pigments are secondary metabolites produced by the fungus. Pigments of mushrooms may protect the organism from UV damage and bacterial attack or play a role as insect attractants. Pigments may contain molecules that are antioxidative, anticarcinogenic, immunomodulatory, antiviral, and antibacterial (Isaac 1994).

 

Pigmented spores have been shown to be more resistant across a variety of environmental conditions compared to unpigmented spores. Pigments provide advantages to fungi such as through protecting them from bright sunlight and some ultraviolet (UV) wavelengths in sunlight.  An experiment showed that spores containing carotenoid pigments had enzymes that were still functional over longer periods of time (Isaac 1994).


Mushrooms do not contain the same pigments found in plants such as chlorophylls and anthocyanins. Many of the pigments of higher fungi are quinones or structures that are mostly classified according to the perceived biosynthetic pathways (VELÍŠEK & CEJPEK 2011) . 

 

Fungi pigmentation may vary with the age and environmental factors and some also undergo distinctive colour changes on bruising. Colours of fruit bodies, spores and colour changes to bruised flesh, are usually essential features used in the identification of fungi.

Carotenoids are terpinoides created from mevalonic acid as a secondary metabolite and are widely found across many fungi. Carotenoids located within structures such as hyphal walls or within oil droplets in membranes, are responsible for the various orange, orange-reds, orange-yellows and dark reds observed across fungi with this pigment (Isaac 1994).

Melanin and sporopollenins are found in spore walls and are thought to enhance spore survival by offsetting the impacts of damaging radiation, enzymes and drying out (Isaac 1994).

The striking orange-red pigments of the cap of fly agaric Amanita muscaria (L.) Hook, are a mixture of the purple betacyanin muscapurpurin, orange betaxanthins muscaurins (muscaaurins) and yellow muscaflavin. Muscaurins are derived from unusual non-protein amino acids ibotenic acid and stizolobic acid,respectively, and are the major agaric pigments (VELÍŠEK & CEJPEK 2011).Pigments containing Nitrogen – betalain pigments in Amanita muscaria 'red' also colours beetroots (Hanson 2008).

The major pigments of the order Boletales are the yellow pulvinic acids that are formed after the terphenylquinone ring has been oxidized and opened. Xerocomic and variegatic acids play the most important role being responsible for the blue colours acquired in many boletes after their fruiting bodies are injured

The yellow pigment characteristic of the yellow-staining Agaricus xanthodermus mushrooms and of
some other Agaricus species happens when leucophenol in the damaged tissue is oxidized forming the azaquinone metabolite agaricone. Some of the pink-red colour stains in some agarics are due to further oxidation of a quinone (VELÍŠEK & CEJPEK 2011).

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The blue colour of genus Chlorociboria is provided by the blue-green pigment Xylindein. Wood stained with this pigment was used in woodcraft and art since at least the 15th century (Robinson et al. 2014 ) and has even been explored as a possible organic semi-conductor for electronics (Giesbers et al. 2018).

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References: 

Giesbers, G., Van Schenck, J., Vega Gutierrez, S., Robinson, S. & Ostroverkhova, O. (2018) Fungi-Derived Pigments for Sustainable Organic (Opto)Electronics, MRS Advances,  https://doi.org/10.1557/adv.2018.446

Hanson, J. (2008) The Chemistry of Fungi, Royal Society of Chemistry.

Isaac, S. (1994) Mycology Answers: Many fungi are brightly coloured; does pigmentation provide any advantage to those species?, Mycologist, vol.8, part 4.

Robinson, S.C., Weber, G., Hinsch, E., Gutierrez, S.M.V., Pittis, L. & Freitas, S. (2014) Utilizing Extracted Fungal Pigments for Wood Spalting: A Comparison of Induced Fungal Pigmentation to Fungal Dyeing, Journal of Coatings, v. 2014, http://dx.doi.org/10.1155/2014/759073

VELÍŠEK, J. & CEJPEK, K. (2011) Pigments of Higher Fungi: A Review, Czech J. Food Sci., v.29, pp. 87–102.

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