Abstract
A systematic review of literature data on the antifungal potential of extracted lichen compounds and individual secondary metabolites against mold species of the genus Aspergillus is provided. Crude extracts from 49 epiphytic, 16 epigeic and 22 epilithic species of lichens and 44 secondary metabolites against 10 species, Aspergillus candidus, A. flavus, A. fumigatus, A. nidulans, A. niger, A. ochraceus, A. parasiticus, A. restrictus, A. stellatus and A. ustus, were analysed. Several measuring techniques were employed for such analyses. Lichen substances were extracted with alcoholic and other organic solvents mainly using the Soxhlet apparatus. Among the three most-studied mold species, the results showed that the crude extracts from the thalli of the lichens Cladonia foliacea, Hypotrachyna cirrhata, Leucodermia leucomelos, Platismatia glauca and Pseudevernia furfuracea against Aspergillus flavus, from C. foliacea, Nephroma arcticum and Parmelia sulcata against A. fumigatus and from Evernia prunastri, Hypogymnia physodes, Umbilicaria cylindrica and Variospora dolomiticola against A. niger have the greatest antifungal potential. The lichen secondary metabolites showed a higher inhibitory potential, e.g. protolichesterinic acid against A. flavus, lecanoric acid against A. fumigatus and orsellinic acid against A. niger; the other seven species of Aspergillus have been poorly studied and require further investigation. A comparison of the inhibitory potential of the tested mixtures of lichen substances and their secondary metabolites shows that they can compete with commonly used antifungal substances, such as ketoconazole and clotrimazole against A. flavus, A. nidulans, A. niger and A. parasiticus and fluconazole in the case of A. fumigatus.
Highlights
Lichens are fundamentally a symbiotic system consisting of a photosynthetic alga or cyanobacterium and heterotrophic fungus, usually an Ascomycota (Armaleo et al 2019), but occasionally a Basidiomycota (Furmanek et al 2019) (172 species: 0.9%: Lücking et al 2017); to date, there are c. 20,000 known lichen species (Lücking et al 2017; Armaleo et al 2019)
Six secondary metabolites of lichens grouped into five biochemical classes were investigated against Aspergillus ochraceus according to the minimal inhibitory concentration (MIC) method, of which diffractaic acid inhibited the strongest (5.2 × 1 0–3 mg ml−1) compared to the weakest activity of orsellinic acid (14.5 × 1 0–3 mg ml−1) (Table S9)
Six secondary metabolites of lichens grouped into five biochemical classes were investigated against Aspergillus nidulans according to the MIC method
Summary
Lichens are fundamentally a symbiotic system consisting of a photosynthetic alga or cyanobacterium and heterotrophic fungus, usually an Ascomycota (Armaleo et al 2019), but occasionally a Basidiomycota (Furmanek et al 2019) (172 species: 0.9%: Lücking et al 2017); to date, there are c. 20,000 known lichen species (Lücking et al 2017; Armaleo et al 2019). Lichens are fundamentally a symbiotic system consisting of a photosynthetic alga or cyanobacterium and heterotrophic fungus, usually an Ascomycota (Armaleo et al 2019), but occasionally a Basidiomycota (Furmanek et al 2019) (172 species: 0.9%: Lücking et al 2017); to date, there are c. 20,000 known lichen species (Lücking et al 2017; Armaleo et al 2019). The lichen produces a wide range of primary metabolites, such as polysaccharides, proteins, dyes (chlorophyll, carotenoids) and vitamins (Elix and Stocker-Wörgötter 2008; Spribille et al 2020), but due to the complexity of the symbiosis, it is not always possible to accurately determine the origin of their biosynthesis (Elix and StockerWörgötter 2008; Ranković and Kosanić 2015). The qualitative composition of polysaccharides depends on their synthesis by the biocomponents of lichens, mainly the
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