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Yeast Tolerance to Chromium Depends on Extracellular Chromate Reduction and Cr(III) Chelation 

Halyna Ksheminska1, Daria Fedorovych2, Taras Honchar1, Maria Ivash1 and Mykhailo Gonchar1,3*


1
Department of Analytical Biotechnology, Institute of Cell Biology, NAS of Ukraine, Drahomanov Str. 14/16, UA-79005 Lviv, Ukraine

2Department of Molecular Genetics and Biotechnology, Institute of Cell Biology, NAS of Ukraine, Drahomanov Str. 14/16, UA-79005 Lviv, Ukraine
3Branch Campus of the Faculty of Biotechnology, Rzeszow University, ul. Sokołowska 26, PL-36-100 Kolbuszowa, Poland

Article history:

Received September 18, 2007
Accepted May 15, 2008

Key words:

yeast, Pichia guilliermondii, chromate tolerance, medium composition, chromate reduction, chromium(III) chelation

Summary:

The sensitivity of the yeast Pichia guilliermondii ATCC 201911 (L2) to Cr(VI) and Cr(III) has been investigated. This yeast was demonstrated to have much higher resistance to Cr(III), compared to Cr(VI). At chromate level of 2.0 mM, an expanded lag phase in growth was observed, followed by the active phase of cell proliferation. During the growth arrest, a residual external chromate concentration decreased gradually to the nontoxic level, and the duration of this period was directly dependent on the initial Cr(VI) concentration in the medium, i.e. the higher the Cr(VI) level, the longer the growth delay. Thus, the tolerance of P. guilliermondii to chromate depends on its capacity for extracellular reduction of Cr(VI). As a product of chromate reduction, Cr(III) forms complexes with the components of culture liquid, which are not effectively adsorbed by the cells and do not repress the growth of P. guilliermondii. When urea is used as a nitrogen source, not only chromate reduction, but also Cr(III) chelation were shown to decrease, compared to the medium supplemented with ammonium sulphate. The experimental data confirm this concept of extracellular reduction of Cr(VI) as an important mechanism, which provides the resistance of yeast cells to chromate.

 


*Corresponding author:           gonchar@cellbiol.lviv.ua
                                               ++38 032 2612 144
                                               ++38 032 2612 108

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