Two yeast strains already identified as Pichia kudriavzevii AM-4 and Candida sp. PSM-33 were able to resist Cr(VI) up to 400 and 350 mg/dm3, respectively. The stability and optimum temperature of chromate reductase in both yeast strains was maximal at 30 °C. Candida sp. PSM-33 showed the higher chromate reductase activity at pH 5 whereas P. kudriavzevii AM-4 exhibited maximum activity at pH 7. Both chromate reductases (ChRs) activities were enhanced in the presence of Mg, Na, Co, and Ca but strongly inhibited by Hg cations. The total cell Cr(VI) uptake capabilities were 15–68 mg/g in Candida sp. PSM-33 and 17–73 mg/g in P. kudriavzevii AM-4 within 2–12 days of growth. It was found that 23–94% of Cr(VI) reduction was achieved by P. kudriavzevii AM-4 while Candida sp. PSM-33 showed 21–88% reduction at a concentration of 100 mg/dm3. Proteins extracted from P. kudriavzevii AM-4 and Candida sp. PSM-33 followed by one-dimensional electrophoresis revealed enriched bands of low molecular-weight metallothioneins (MTs) suggesting some differential proteins could be expressed under Cr(VI) treatment. Both yeast strains can be used to ameliorate the wastewater contaminated with toxic metal ions.
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