Biological activity of some common lichens

Abstract

Lichens, are symbiotic organisms of fungal and an algal and/or cyanobacterial partner and are considered edible or used for their medicinal properties by many cultures. They produce a variety of secondary compounds unique to lichens, mostly from fungal metabolism. In spite of the diversity few studies have evaluated the biological activity of secondary metabolites from lichens. Our objective was to evaluate the antioxidant, antimicrobial and anti‐adhesive activity of common lichens in Central Texas against Pseudomonas aeruginosa. Lichens were harvested from trees and rocks using standard techniques and identified by morphological, biochemical and microscopic analysis. The low molecular weight fraction (LMWF) and high molecular weight fraction (HMWF) were isolated using standard protocols. Antioxidant activity was determined by Malondialdehyde (MDA) assay and radical quenching assay. Antimicrobial and anti‐adhesive activity of sterile extracts against P. aeruginosa was determined by Kirby‐Bauer (KB) and ex vivo skin assay respectively. Lichens harvested were identified as Ramalina celastri (RA), R. stenospora (RS), R. Americana (RA), T. chrysopthalmus (TC), Parmotrema austrosinese (PA) and P. perforatum (PP). The HMWF had higher antioxidant activity and neutralized 60‐75% radicals compared to LMWF which only neutralized 20‐40% of the radicals except PA whose activity was 79%. All extracts were able to reduce MDA formation by 30‐88% except LMWF of RA and PP. None of the extracts had antimicrobial activity in the KB assay. All the HMWF were able to reduce adhesion of P. aeruginosa by 30‐55% except PP. LMWF from RS, PP, PA and PP reduced bacterial adhesion by 41‐54%. Our results suggest that Lichens can be an important source for bioactive compounds with benefits against oxidative and infectious diseases and warrants further investigation.