Heavy metal tolerance of fungi

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 subculturing 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. (C) 2001 Elsevier Science Ltd. All rights reserved.