Evaluating Aspergillus terreus tolerance to toxic metals

Introduction: Metal pollution is one of the major environmental problems. Some metals are toxic at very low concentrations, bioaccumulate and do not decompose to non-toxic forms. Objective: To isolate a strain of microscopic fungus in a site contaminated with toxic metals and to evaluate the tolerance to these substances. Materials and methods: Fungi were isolated from the soil of an abandoned lead mine. Tolerance index of fungi to cadmium, mercury and lead was evaluated individually at concentrations of 50, 100, 250, 350 and 500 ppm; in addition, a multimetal system (mixture) with cadmium, chromium, mercury and lead was evaluated at 4, 8, 16, 64, 80, 120, 200 and 400 ppm. The minimum inhibitory concentration (MIC) was also determined. Results and discussion: The isolated fungi were identified as Aspergillus terreus, which showed high tolerance indices for lead (0.9) at all concentrations tested and indices of 0.8 at most mercury concentrations. Cadmium was the most toxic metal; tolerance indices of 0.56 and 0.2 were observed at 50 ppm and 100 ppm, respectively. High tolerance indices (0.9) were observed in the multimetal system up to 64 ppm. MIC was greater than 500 ppm with lead and mercury, less than 250 ppm with cadmium and greater than 400 ppm with the multimetal system. Conclusion: A. terreus showed high tolerance to lead at all concentrations tested. The level of tolerance is influenced by the type of metal.