A zinc (Zn)-tolerant fungus, designated BC109-2, was isolated from rhizosphere soil and was identified as Penicillium janthinellum BC109-2 based on ITS sequence analysis. To understand its Zn tolerance mechanisms, a series of studies was carried out addressing the subcellular distribution of Zn, its chemical forms, and the antioxidant system (superoxide dismutase, catalase, peroxidase, glutathione reductase, glutathione S-transferase, reduced glutathione, oxidized glutathione and malondialdehyde) of the fungus. The maximum level of resistance to Zn for strain BC109-2 is 2100 mg L-1. The Zn contents and percentages of cell wall and soluble fraction increased with increasing Zn concentration in the medium, which indicated extracellular accumulation/precipitation and vacuolar compartmentation mechanism might play significant role in the detoxificating process. The proportion of inactive forms of Zn was higher in the fungus, which indicated that BC109-2 mainly formed inactive Zn and stored it in the cell walls and vacuoles to decrease Zn toxicity. Furthermore, changes in antioxidant enzyme activities at various concentrations of Zn showed that the addition of Zn could cause oxidative stress in the fungal cells and that antioxidant enzymes in fungi played important roles in resistance to Zn toxicity. Moreover, the high level of lipid peroxidation showed that the protective effects of the antioxidant system were not sufficient at the high concentrations of Zn even though the antioxidant enzyme activity levels were very high. The purpose of this work is to figure out the heavy metal tolerance mechanisms of microorganisms in soil and the microbial isolate could be potentially used in bioremediation of Zn-contaminated environments.
Keywords: Antioxidant system; Chemical forms; Subcellular distribution; Tolerant mechanisms; Zn tolerance.