Phytochemical Analysis, Antimicrobial, Antibiofilm and Antioxidant Effects of a New Arctic Lichen Placidium Doesaiense Growing in Pakistan

Lichenochemical composition and antimicrobial, antibiofilm and antioxidant effects of a newly described arctic lichen Placidium doesaiense growing in Pakistan were investigated. HPLC–DAD methods were used for identification of secondary metabolites in acetone and methanol extracts. The total polyphenol and the total flavonoid content was determined spectrophotometrically. The study examined the antioxidant (DPPH scavenging activity and reducing power), antibacterial (minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC)) and antibiofilm (inhibition of biofilm formation and reduction of mature biofilm) activities of extracts of the lichen P. doesaiense and isolated parietin. The chemical constituents olivetol, olivetolic acid, haematommic acid, fallacinol and parietin, were identified as major compounds in the tested extracts of the lichen. Parietin was isolated from the acetone extract on a separation column. The methanol extract had higher values of TPC (21.67 mg GA/g) and TFC (377.40 mg RE/g) than the acetone extract. Although the extracts showed the best antibacterial activity (especially against Proteus mirabilis ATCC 12453), parietin demonstrated superior antibiofilm activity (especially against Staphylococcus aureus ATCC 25923). Isolated parietin showed the best antioxidant activity measures according to DPPH scavenging activity (IC50= 51.616 μg/mL) and reducing power. This is the first report on the phytochemical composition of the lichen Placidium doesaiense and the first description of the chemical composition of some of the 28 species of the genus Placidia. This research will pave the way for further exploration of new activities of this lichen and its metabolites, which are important for medicine and pharmacy.