Biological activity of Pinus nigra terpenes - Evaluation of FtsZ inhibition by selected compounds as contribution to their antimicrobial activity

In the current work, in vitro antioxidant, antibacterial, and antifungal activites of the needle terpenes of three taxa of Pinus nigra from Serbia (ssp. nigra, ssp. pallasiana, and var. banatica) were analyzed. The black pine essential oils showed generally weak antioxidative properties tested by two methods (DPPH and ABTS scavenging assays), where the highest activity was identified in P. nigra var. banatica (IC50=25.08 mg/mL and VitC=0.67 mg (vitamin C)/g when tested with the DPPH and ABTS reagents, respectively). In the antimicrobial assays, one fungal (Aspergilus niger) and two bacterial strains (Staphylococcus aureus and Bacillus cereus) showed sensitivity against essential oils of all three P. nigra taxa. The tested oils have been shown to possess inhibitory action in the range from 20.00 to 0.62 mg/mL, where var. banatica exhibited the highest and ssp. nigra the lowest antimicrobial action. In order to determine potential compounds that are responsible for alternative mode of action, molecular docking simulations inside FtsZ (a prokaryotic homolog of tubulin) were performed. Tested compounds were the most abundant terpenoid (germacrene D-4-ol) and its structurally similar terpene (germacrene D), both present in all three essential oils. It was determined that the oxygenated form of the molecule creates stable bonds with investigated enzyme FtsZ, and that this compound, through this mechanism of action participates in the antimicrobial activity.