Fungi are commonly known to produce a range of natural products called secondary metabolites that have been utilised in the medical, industrial and agricultural fields (Calvo, 2002). Like plants, certain fungi also produce natural dyes or pigments such as betalains, carotenoids, and terpenoids. While these pigments may play a defensive role in protecting the fungus from environmental harm such as ultraviolet radiation or microbial infection, research on these colourful chemical constituents from fungi revealed many of them to be biologically active with antibacterial, anticarcinogenic, antioxidative, antiviral, and other pharmaceutical properties (Velíšek, 2011).
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An endophytic fungus found in the rainforest of Sarawak is one of such pigment-producing strains. Endophytes are microorganisms that live within the tissue of plants, and this fungus was isolated from the leaves of a Dysoxylum plant (Meliaceae) collected from a forest reserve. Despite its woolly white mycelia, the fungus molecularly identified as Khuskia oryzae, coloured the culture media ruby-red when grown on potato dextrose agar. As the culture aged and the mycelia spread to cover the entire agar surface, the colour of the agar gradually transitioned to a darker hue of red closer to purple. Interestingly, the fungus appears to be selective on the type of media it decides to colour. For example, when cultured on cornmeal agar the fungus did not produce its characteristic red and the agar remained colourless.
Antitumour bioassay done on the fungus extract has shown it to be moderately cytotoxic to certain human cancer cell lines. Antimicrobial assay also showed moderate inhibition activity against Staphylococcus aureus, a species of common bacterium known to cause skin infections such as boils and pimples to serious illnesses including pneumonia.
Whether these biological activities are related to the red pigment produced by the fungus will require further investigation, although it has been observed that the extract’s cytotoxic activity varies according to culture age as does the intensity of the red colour.
References:
Calvo, A., Wilson, R.A., Bok, J.W., Keller, N.P. (2002): Relationship Between Secondary Metabolism and Fungal Development. Microbiology and Molecular Biology Reviews 3(66): 447-459.
Mussak R., Bechtold T. (2009): Handbook of Natural Colorants. John Wiley & Sons, New York: 183–200.
Velíšek J., Cejpek K. (2011): Pigments of higher fungi – a review. Czech Journal of Food Science, 29: 87–102.
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