Background: Lichens that were used in traditional medicine for ages produce numerous secondary metabolites, however our knowledge about biological activities of substances secreted by separated bionts is scarce. The main objectives of this study were to isolate and find optimal conditions for the growth of mycelia from three common lichen-forming fungi, i.e. Caloplaca pusilla, Protoparmeliopsis muralis and Xanthoria parietina and to evaluate antibacterial and antiproliferative activities of their acetone extracts.
Methods: Agar disc diffusion and broth microdilution methods were used to test antimicrobial activity against six species of bacteria. MTT method, flow cytometry assay and DAPI staining were applied to test antiproliferative activity of selected extracts against MCF-7 (human breast adenocarcinoma), PC-3 (human prostate cancer) and HeLa (human cervix adenocarcinoma) cancer cells.
Results: P. muralis strongly inhibited the growth of Gram-positive bacteria, i.e. Bacillus subtilis, Enterococcus faecalis, Staphylococcus aureus and Staphylococcus epidermidis (MICs from 6.67 to 100.00 μg mL-1). X. parietina grown on PDA and G-LBM media decreased HeLa or MCF-7 cancer cells viability with IC50 values of about 8 μg mL-1, while C. pusilla grown on G-LBM medium showed the highest potency in decreasing MCF-7 (7.29 μg mL-1), PC-3 (7.96 μg mL-1) and HeLa (6.57 μg mL-1) cancer cells viability. We also showed induction of apoptosis in HeLa, PC-3 and MCF-7 cell lines treated with increasing concentrations of C. pusilla extract.
Conclusion: We showed that selected acetone extracts demonstrated a strong antimicrobial and anticancer effects that suggests that aposymbiotically cultured lichen-forming fungi can be a source of antibacterial and antiproliferative compounds.
Keywords: Antibacterial activity; Antiproliferative effect; Apoptosis; Lichen; MBC; MIC.