Role of the component Fre1p of the plasma membrane ferric reductase on the azo reductase activity of intact Saccharomyces cerevisiae cells

Abstract

Unspecific bacterial reduction of azo dyes is a widely studied process in correlation with the biological treatment of coloured waste waters but the enzyme system associated to this bacterial capability has never been positively identified. Several ascomycete yeast strains display similar decolourising activities. 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 Saccharomyces cerevisiae mutant strains Δfre1 and Δfre1Δfre2, but not Δfre2, showed a much reduced decolourising capability, suggesting that, under the conditions tested, Fre1p is a major component of the azo reductase activity.