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Applied and Environmental Microbiology, July 2005, p. 3882-3888, Vol. 71, No. 7
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.7.3882-3888.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Azo Reductase Activity of Intact Saccharomyces cerevisiae Cells Is Dependent on the Fre1p Component of Plasma Membrane Ferric Reductase

Patrícia A. Ramalho,1 Sandra Paiva,1 A. Cavaco-Paulo,2 Margarida Casal,1 M. Helena Cardoso,1* and M. Teresa Ramalho3

Department of Biology, University of Minho, Campus de Gualtar, 4710-057 Braga,1 Department of Textile Engineering, University of Minho, Campus de Azurém, 4800-058 Guimarães,2 Department of Chemistry, University of Minho, Campus de Gualtar, 4710-057 Braga, Portugal3

Received 26 July 2004/ Accepted 22 January 2005

Unspecific bacterial reduction of azo dyes is a process widely studied in correlation with the biological treatment of colored wastewaters, but the enzyme system associated with this bacterial capability has never been positively identified. Several ascomycete yeast strains display similar decolorizing behaviors. The yeast-mediated process requires an alternative carbon and energy source and is independent of previous exposure to the dyes. When substrate dyes are polar, their reduction is extracellular, strongly suggesting the involvement of an externally directed plasma membrane redox system. The present work demonstrates that, in Saccharomyces cerevisiae, the ferric reductase system participates in the extracellular reduction of azo dyes. The S. cerevisiae {Delta}fre1 and {Delta}fre1 {Delta}fre2 mutant strains, but not the {Delta}fre2 strain, showed much-reduced decolorizing capabilities. The FRE1 gene complemented the phenotype of S. cerevisiae {Delta}fre1 cells, restoring the ability to grow in medium without externally added iron and to decolorize the dye, following a pattern similar to the one observed in the wild-type strain. These results suggest that under the conditions tested, Fre1p is a major component of the azo reductase activity.

* Corresponding author. Mailing address: Department of Biology, University of Minho, Campus de Gualtar, 4710-057 Braga, Portugal. Phone: (351) 253 604043. Fax: (351) 253 678980. E-mail: mhc{at}bio.uminho.pt.

Applied and Environmental Microbiology, July 2005, p. 3882-3888, Vol. 71, No. 7
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.7.3882-3888.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.



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