Tolerance to Heavy Metals by Some Fungal Isolates from Petroleum Refinery Effluent in Kaduna, Nigeria

Investigation was carried out to assess the potential of some fungal species to tolerate and grow in biomassin vitro in the presence of some heavy metals (HMs) (Pb, Zn, Cr and Cd) from Kaduna Refinery and Petrochemical Company (KRPC) effluent. This was done by subjecting all the fungal isolates through the tolerant test (biomass production). The isolates were inoculated into replicate 100 ml flask containing 50 ml of Potato Dextrose Agar (PDA) amended with 5, 10 and 15 ppm of Pb, Zn, Cr, and Cd. Each test isolate was inoculated into replicate flask containing the same medium without the HMs to serve as control. All inoculated flasks were incubated aerobically at room temperature on a rotatory shaker for 7 days. The mycelial mats were harvested by filtering the cultures through preweighed filter paper (No.1). The filters containing the mycelial mats were dried in an oven at 70 for 18 hours. It was observed that most of the isolates tested tolerated and grew in the medium containing 5 to 15 ppm of tested HMs. Yield of dry mycelia mats in the heavy metal supplemented medium were also comparable to those grown in heavy metal free PDA medium. Three fungal species- Aspergillus niger, Aspergillus flavus and Microsporum nanum isolated from the refinery were found to be most tolerant to varying concentration of heavy metals (Pb, Zn, Cr and Cd). A. niger is most tolerant to 5 µg/ml, 10 µg/ml, and 15 µg/ml concentration of HMs followed by M. nanum, A. flavus and Penicillium marneffei. Aspergillus fumigatus, Chaetomium sp., Cunninghamella bertholletiae, Trichophyton tonsurans and Nigrospora sp. were less tolerant to the heavy metal concentrations. These three most tolerant fungal isolates (M. nanum, A. flavus and Penicillium) may be important in treating systems contaminated with heavy metals (HMs) because of their bioremediation potential.