Abstract:

Abstract The main objective of this study was to investigate the variations in the content of polyphenols and flavonoids in lead-stressed X. parietina (L.) Th. Fr. lichen and to study the antibacterial activity of its methanol extract, Lichen thalli have been incubated at lead concentrations of 0, 0.5, 1.0, 5.0 and 10.0 mM for 96 hours. The antibacterial activity of methanol extract was evaluated against three Gram-positive bacteria (Bacillus cereus, Staphylococcus aureus and Listeria monocytogenes) and five Gram-negative bacteria (Escherichia coli, Klebsiella pneumoniae, Salmonella typhimurium, Pseudomonas aeruginosa and Enterobacter spp.) The analysis of the obtained results data showed that X. parietina is able to accumulate lead correlating with Pb(NO3)2 availability in the substrate, it also highlight that lead-induced stress causes significant increase in polyphenol and flavonoid contents with increasing Pb(NO3)2 concentrations, but with high concentrations, polyphenol and flavonoid contents decrease . Furthermore, results show a positive correlation between the polyphenol, flavonoid contents and the variations of the size of the inhibition zone diameter. Based on these results, Gram-negative bacteria were shown to be more resistant to the extracts than Gram-positive- bacteria.

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