Evidences for antioxidant response and biosorption potential of Bacillus simplex strain 115 against lead

In this study, we investigated effects of lead on growth response and antioxidant defense protection in a new identified strain isolated from a soil, in the rhizosphere of Sainfoin Hedysarum coronarium L. Different concentrations of lead (0, 0.2, 1.5 and 3 g L^-1) added to Bacillus simplex strain 115 cultures surprisingly did not inhibit its growth. However, a resulting oxidative stress as attested by overproduction of H₂O₂ (+ 6.2 fold) and malondialdehyde (+ 2.3 fold) concomitantly to the enhancement of proteins carbonylation (+ 221%) and lipoxygenase activity (+ 59%) was observed in presence of 3 g L^-1 of lead. Intrinsic antioxidant defenses were revealed by the coupled up-regulation of catalase (+ 416%) and superoxide dismutase (+ 4 fold) activities, with a more important Fe-SOD increase in comparison to the other isoforms. Bioaccumulation assays showed both intracellular and extracellular lead accumulation. Biosorption was confirmed as a particularly lead resistance mechanism for Bacillus simplex strain 115 as the metal sequestration in cell wall accounted for 88.5% to 98.5% of the total endogenous metal accumulation. Potentiality of this new isolated microorganism as a biotechnological tool for agricultural soil lead bioremediation was thus proposed.