During bioleaching of Cobalt from waste lithium-ion batteries, the biooxidation activity of acidophilic bacteria is inhibited by a high concentration of Co ion in the liquid phase. However, the mechanism for Co2+ toxicity to acidophilic bacteria has not been fully elucidated. In this study, the effects of Co2+ concentration on the biooxidation activity for Fe2+, intracellular reactive oxygen species (ROS) level and antioxidant defense systems in a mixed-culture of acidophilic bacteria (MCAB) were investigated. The results showed that the biooxidation activity of the MCAB was inhibited by Co2+. Furthermore, it was indicated that the intracellular ROS contents of the MCAB under conditions of 0.4 M and 0.6 M Co2+ were 2.60 and 3.34 times higher than that under the condition of 0 M Co2+. The increase in intracellular malondialdehyde content indicated that the oxidative damage was induced by Co2+. Moreover, the antioxidant systems in MCAB were affected by Co2+. It was observed that the Co2+ exposure increased the catalase and glutathione peroxidase activities while reducing the superoxide dismutase activity and the intracellular glutathione (GSH) content. It was found that an exogenous GSH supplementation eliminated excess intracellular ROS and improved the biooxidation activity of the MCAB.
