Interrelations of the yeast Candida utilis and Cr(VI): metal reduction and its distribution in the cell and medium

Abstract

An effect of chromium(VI) ions on the growth and bioaccumulation properties of growing cells of Candida Utilis was studied. Molasses media for yeast growth containing 20 g glucose l −1 and 50+500 mg Cr(VI) l −1 were used in batch cultivation. Addition of 100 mg Cr(VI) l −1 resulted in a threefold decrease in the cell concentration, as compared with the culture grown without metal. Cr(VI) inhibited culture growth in a concentration-dependent manner, this dependence was not linear. Glucose consumption by growing cells depended on the initial Cr(VI) concentration in the medium and correlated with growth activity. No inhibitory effect of high Cr(VI) concentrations on the activity of some exo-enzymes of C. utilis cells was observed. During C. utilis cultivation, Cr(VI) was partially reduced to an ultimate Cr(III) in all tested ranges of the Cr(VI) concentrations. The specific chromium uptake by cells was detected in biomass that grew in the presence of 100+300 mg Cr(VI) l −1 in a period of 48–96 h. The highest values were achieved after 96 h growth in the presence of 200 and 300 mg Cr(VI) l −1, and were 7.3 and 7.2 mg Cr g dw l −1, respectively. Electron microscopic observations showed morphological changes in yeast cells to be more pronounced upon culture growth with 100–300 mg Cr(VI) l −1 than in the cells subjected to higher metal concentrations. The conclusion has been made that the mechanism of the Cr(VI) toxic effect on the growing yeast cells can vary in dependence of the metal concentration.