Melanin Production by the Medicinal Mushroom Inonotus obliquus F-1375 in Submerged Liquid Cultivation and its Antiretroviral Properties

We have explored the effect of a new strain of the mushroom Inonotus obliquus (Ach.:Pers.) Pilat (Basidiomycota) F-1375 on melanin production in a glucose–tryptone medium, while adding a preparation of betulin and chemically pure tyrosine, under electric lighting and under dark conditions. The betulin preparation in the examined concentrations had practically no effect on the production of melanin, while high concentrations of tyrosine stimulated the production of melanin, both under illumination and in the dark. All studied samples of mushroom melanin are nontoxic: both isolated from natural (TC₅₀ = 96 ± 8 μg/mL) and cultured in a liquid medium with the addition of betulin and tyrosine (TC₅₀ from 164 to 400 μg/ml) are active against HIV-1 in an MT-4 cell culture (IC₅₀ 1 to 4.3 μg/mL, SI 17 to 192). The selectivity indices of the preparations of melanin of cultivated Inonotus obliquus F-1375 against the human immunodeficiency virus subtype A were at the level of 33-192, which makes it possible to recommend them for the development of antiviral agents. Melanin from the mushroom Inonotus obliquus F-1375 cultured in electric light with the addition of 10 and 20 mM tyrosine had the highest selectivity index for the HIV-1 retrovirus (SI 192).