Pergamon 0892-6875(01)00037-1 Minerals Engineering, Vol. 14, No. 5, pp. 499-505, 2001 © 2001 Elsevier Science Ltd All rights reserved 0892-6875/01/$ - see front matter HEAVY METAL TOLERANCE OF FUNGI* M. VALIX, J.Y. TANG and R. MALIK Department of Chemical Engineering, The University of Sydney, NSW 2006, Australia E-mail: mvalix @chem.eng.usyd.edu.an (Received 11 December 2000; accepted 17 February 2001) ABSTRACT The tolerance of fungi strains including Penicillium funiculosum, Aspergillus foetidus, Penicillium simplicissimum for different heavy metals, which could be leached, from nickel laterite ores (Ni, Co, Fe, Mg and Mn) was studied. These strains were exposed to heavy metals up to 2000 ppm. The tolerant strains were selected by repeated subcutturing in petri dishes with increasing metal concentration in the medium. The degree of tolerance was measured from the growth rate in the presence of the various heavy metals and compared to a control, which contained no heavy metals. It appears that Penicillium funiculosum and Aspergillus foetidus were the most tolerant to the heavy metals and exhibited strong growth often exceeding the control. Penicillium simplicissimum showed the least tolerance particularly for Ni and Co. A growth pattern, which was consistent for each strain under various heavy metals, was observed as a function of time. The growth pattern of the fungi exhibited a lag, retarded, similar and enhanced rate of growth in the presence of heavy metal relative to the control. The similarity in the pattern appears to suggest the tolerance development or adaptation of the fungi for heavy metals. © 2001 Elsevier Science Ltd. All rights reserved. Keywords Oxides ores; bioleaching INTRODUCTION Nickel laterite ores, have been shown to be amenable to leaching by heterotrophic microorganism and their metabolic products (Valix et. al, 2000, Boseker, 1985, Tzeferis et.al., 1994). Development and optimisation of such a process will depend on the isolation of microorganism, which would be tolerant to various conditions, including temperature, pH and heavy metal concentrations during the leaching process. Understanding the interaction between heavy metals and microorganisms has perhaps attracted the most interest to researchers due to its application in metallurgy and decontamination of the environment. Heavy metals in small concentrations can induce morphological changes and then destroy the microorganism cell. At relatively high concentrations heavy metals act as a general protoplasmic poison, inducing denaturation of proteins and nucleic acid (Avakyan, 1994). Despite the natural actions of heavy metal on the microorganism, they demonstrate an ability to survive by adapting and mutating under various conditions including high concentrations of heavy metals. The control of such operations will allow strain to be tailor made for specific applications and would greatly improve the biological application of these microorganisms to mineral processing and for environmental protection. Isolation of strains with tolerance to Ni has been conducted by Boseker, 1985, Tzeferis et.al., 1994, Tzeferis, 1994, with favourable results. However in leaching nickel laterites ores, various metals, including * Presented at Minerals Engineering 2000, Cape Town, South Africa, November 2000 499