Investigation of Antimicrobial and Antioxidant Activity of Tephromela atra Lichen and its Chemical Isolates, α-Alectoronic Acid and α-Collatolic Acid

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Abstract
Lichens and their secondary metabolites are of particular interest as they can be used as an alternative to synthetic drugs in the treatment of various diseases. The present study was carried out to investigate in vitro antioxidant and antimicrobial activities of acetone, dichloromethane, petroleum ether, and methanol extracts of the lichen Tephromela atra and its major metabolites. α-alectoronic acid and α-collatolic acid were identified as bioactive substances in the lichen Tephromela atra . The antibacterial activity was investigated using the disk diffusion method and the minimum inhibitory concentrations were determined against eleven bacterial species, nine fungal species, and four yeast species using broth microdilution method. The antioxidant activity of the methanol extracts of Tephromela atra was measured by the free radical scavenging ability using the DPPH method. The extracts of α-alectoronic acid and α-collatolic acid showed significant inhibitory activity against most of the tested bacteria, especially the lowest MIC values of the two acids for Bacillus subtilis . Furthermore, the antioxidant activity was determined in vitro by measuring the radical scavenging capacity of the extracts on DPPH. The methanol extracts showed significant antioxidant activity and high DPPH scavenging activity at all concentrations. The results indicate that the extracts of Tephromela atra and the natural products obtained can be used as a source of antimicrobial and antioxidant agents in the pharmaceutical industry. HIGHLIGHTS: The present study determines the antibacterial and antifungal activities of the Tephromela atra , lichen extracts, and its isolated major constituents (α-alectoronic acid and α-collatolic acid), as well as evaluates the antioxidant capacity. Although there are some studies on α-alectoronic acid and α-collatolic acid, isolated in different lichens, there is no study on the biological activity and antioxidant capacity of lichen Tephromela atra . The MIC values of isolates were evaluated against a broad range of microorganisms including eleven species of bacteria, nine species of fungi, and four species of yeasts. α-Alectoronic and α-collatolic acid extracts showed significant inhibitory activity against most of the tested bacteria, especially the lowest MIC values of both acids for Bacillus subtilis. Our results provide a future perspective that Tephromela atra extracts and the isolated metabolites might be used as effective antimicrobial and antioxidant agents in pharmaceutical areas. Graphical

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