Toxic metal tolerance of Aspergillus flavus and Aspergillus nidulans isolated from tailings

Introduction: Metals are found naturally in the environment, but their indiscriminate use has caused serious pollution problems. Objective: Two species of Aspergillus were isolated and identified from tailings, then their tolerance index at different concentrations of several metals was evaluated. Materials and methods: Fungi were isolated from tailings located in the Sonoran Desert. Fungal growth was evaluated in the presence of Cr6+, Pb2+, Zn2+, Ag+ , Cd2+, Cu2+ and Hg2+ metals using the tolerance index and minimum inhibitory concentration (MIC). Results and discussion: A. flavus had very high tolerance indices to Cr6+, Pb2+ and Zn2+ at all concentrations evaluated (>20 mM); it also had a high tolerance index to the other metals at lower concentrations. The MIC for this fungus in the presence of Cd2+, Hg2+ and Ag+ was recorded between 5 and 10 mM. The growth of A. nidulans was not inhibited with 20 mM of Cr6+. The MIC of A. nidulans in presence of Hg2+, Ag+ and Cu2+ is in the range 1-5 mM; with Cd2+, Pb2+ and Zn2+ it is in the range between 15 and 20 mM. The dose-response curves display a characteristic sigmoidal shape. With Ag+ and Cu2+ A. flavus displayed a hermetic behavior. Conclusion: High metal tolerance of these fungi suggests their potential use in the removal of metals.