Radical scavenging and antibacterial activity of three Parmotrema species from Western Ghats of Karnataka, India

Western Ghats are one of the biodiversity hotspots in the world. The present study was conducted to determine antibacterial and radical scavenging potential of three Parmotrema species viz., P. tinctorum, P. grayanum and P. praesorediosum from Maragalale and Guliguli Shankara, Western Ghats of Karnataka, India. The powdered lichen materials were extracted using methanol. Antibacterial activity of lichen extracts was tested against three Gram positive and five Gram negative bacteria by Agar well diffusion assay. Radical scavenging activity of lichen extracts was determined by DPPH free radical scavenging assay. Total phenolic content of lichen extracts was estimated by Folin-Ciocalteau reagent method. The lichen extracts showed dose dependent antibacterial activity. Overall, the lichen extracts were more inhibitory to Gram positive bacteria than Gram negative bacteria. P. grayanum displayed high inhibitory activity against test bacteria. Scavenging of DPPH radicals by lichen extracts was concentration dependent. Among the lichen species, P. grayanum showed higher scavenging potential as indicated by lower IC50 value. Total phenolic content was also high in P. grayanum. Thin layer chromatogram revealed the presence of Lecanoric acid, Orsellinic acid, Protolichesterinic acid, Chloroatranorin, Protopraesorediosic acid and Praesorediosic acid in lichen samples. The observed bioactivities of lichens could be ascribed to the presence of secondary metabolites. These lichens can be considered as suitable candidates for development of bioactive agents active against pathogenic microbes and oxidative damage.