Isolated cell walls of the yeast Saccharomyces cerevisiae were treated by either chemical (alkali and acid) or enzymatic (protease, mannanase or beta-glucuronidase) processes to yield partially purified products. These products were partially characterized by infrared analysis. They were subsequently reacted with heavy metal cation solutions and the quantity of metal accumulated by the cell wall material determined. The Cu(2+) ion (0.24, 0.36, 1.12, and 0.60 micromol/mg) was accumulated to a greater extent than either Co(2+) (0.13, 0.32, 0.43, and 0.32 micromol/mg) or Cd(2+) (0.17, 0.34, 0.39, and 0.32 micromol/mg) by yeast cell walls, glucan, mannan, and chitin, respectively The isolated components each accumulated greater quantities of the cations than the intact cell wall. Removal of the protein component of the yeast cell walls by Pronase caused a 29.5% decrease in metal accumulation by yeast cell walls per mass, indicating the protein is a heavy metal accumulating component. The data indicate that the outer mannan-protein layer of the yeast cell wall is more important than the inner glucan-chitin layer in heavy metal action accumulation.

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The bioaccumulation of metals (Cu z+, Cr 6+, Cd 2+, Ni 2+ and Zn 2÷) from three electroplating effluents by viable Saccharornyces cerevisiae, and the effect of glucose treatment on accumulation was determined. Pretreatment of the yeast cells with glucose increased the amount of metal removed, whilst direct addition of glucose to the yeast-effluent solution had no effect on the amount of metal accumulated. INTRODUCTIONThe bioremediation of heavy metals has received a great deal of attention in recent years, not only as a scientific novelty but also for its potential application in industry. Microorganisms are potent bioremediators, removing metals via active or passive uptake mechanisms. One of the most ubiquitous biomass types available on a large scale is S. cerevisiae. Although this biomass has previously been referred to as a mediocre biosorbent (Volesky and Holan, 1995) its ready availability and low cost in certain countries make it a favourable choice of biosorbent in these cases. Furthermore, yeast cells retain their ability to accumulate a broad range of heavy metals to varying degrees under a wide range of external conditions .

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