In the present study, in vitro antioxidant, antimicrobial and cytotoxic activities of acetone extract from the lichens Cladonia furcata, Lecanora atra and Lecanora muralis were examined.
The tested lichen extracts have a strong antioxidant activity against various oxidative systems in vitro. We found that the tested extracts exhibited the highest radical scavenging activity with the greatest amount of phenolic content. The highest value of phenols was seen in the acetone extract of Lecanora atra which exhibited the strongest radical scavenging activity. Based on these results, it could be concluded that antioxidative nature of the extracts might depend on their phenolics. Phenolic components are potential antioxidants, free radical terminators [20, 21]. These compounds are the main agents that can donate hydrogen to free radicals and thus break the chain reaction of lipid oxidation at the first initiation step. This high potential of phenolic compounds to scavenge radicals such as singlet oxygen, superoxide and hydroxyl radicals may be explained by their phenolic hydroxyl groups . Flavonoids are also the most important natural phenolics and they possess a broad spectrum of chemical and biological activities including radical scavenging properties . Numerous researches found a high correlations between antioxidative activities and phenolic content [24–26]. Interestingly, Odabasoglu et al.  reported that in some lichens extracts no correlation was found between the total phenol and the antioxidant activity, suggesting that the antioxidant activity of different lichens may also depend on other, non-phenol components. Antioxidant effect of some other lichens was also studied by other researchers. For example, Gulcin et al.  found that the aqueous extracts of Cetraria islandica had a strong antioxidant activity. Similar results were reported by Behera et al.  for different extracts from the lichen Usnea ghattensis. Kekuda et al.  find an antioxidant activity for the extracts of the lichen Parmotrema pseudotinctorum and Ramalina hossei. Manojlović et al.  explored antioxidant properties of Laurera benguelensis.
In our experiments, the tested lichen extracts show a relatively strong antimicrobial activity. The intensity of the antimicrobial effect depended on the species of lichen, its concentration and the tested organism. The extract of Cladonia furcata had the strongest antimicrobial activity among the tested species in this study, inhibiting the tested bacteria and fungi at low concentrations, while the lowest activity showed Lecanora muralis. Differences in antimicrobial activity of different species of lichens are probably a consequence of the presence of different components with antimicrobial activity [31, 32, 24].
The extracts used in this study, had a stronger antibacterial than antifungal activity. This observation is in accordance with other studies [33, 24], focused on the antimicrobial activity which have demonstrated that bacteria are more sensitive to the antimicrobial activity than the fungi due to differences in the composition and permeability of the cell wall. The cell wall of Gram-positive bacteria is made of peptidoglucanes and teichoic acids, while the cell wall of Gram-negative bacteria is made of peptidoglucanes, lipopolysacharides and lipoproteins [34, 35]. The cell wall of fungi is poorly permeable and it consists of polysaccharides such as hitchin and glucan .
Numerous lichens were screened for antimicrobial activity in search of the new antimicrobial agents. Ranković et al.  find an antimicrobial activity for the methanol extract of the lichens Parmelia centrifuga. Similar results were reported by Candan et al.  for different extracts extracted from the lichen Parmelia sulcata. Goel et al.  found out that lichen Parmelia reticulata had a strong antimicrobial influence.
In present study, the results clearly demonstrate that acetone extracts of studied lichens induced significant cytotoxic effect on the tested cancer cell lines. Until now, only few research proved that lichen extracts have anticancer activity. Bezivin et al.  reported significant anticancer effect for Parmelia caperata, Cladonia convoluta, Cladonia rangiformis, Platisma glauca and Ramalina cuspidata. Manojlović et al.  explored anticancer properties of Thamnolia vermicularis. Trigiani et al.  found strong anticancer activity for Xanthoria parietina.
Some literature data reported that lichen components are responsible for anticancer activities of lichens. Anticancer activity of various lichens components are known, such as: usnic acid, lecanoric acid, gyrophoric acid, salazinic acid, lobaric acid, evernic acid, vulpinic acid, protolichesterinic acid [42, 43]. However, it is difficult to determine the contribution of individual components for the overall anticancer effect. Often, the activity of the extracts may be the result of an synergistic effect of several compounds.