Zinc Uptake and Toxicity in the Yeasts Sporobolomyces roseus and Saccharomyces cerevisiae

Abstract

Sporobolomyces roseus and Saccharomyces cerevisiae accumulated zinc from zinc-containing medium. Uptake was biphasic and consisted of an initial, rapid, metabolism-independent binding of zinc to cell surfaces which was followed by slower, metabolism-dependent intracellular uptake of zinc. Spor. roseus could bind approximately eight times more zinc, per unit surface area, than could S. cerevisiae. Metabolism-dependent zinc uptake followed Michaelis-Menten kinetics with K , values of 0.09 and 5-00 mM-Zn2+ for Spor. roseus and S . cerevisiae, respectively; corresponding V,,, values were 0-5 1 and 9.09 nmol Zn2+ (mg dry wt)-l min-'. Zinc uptake by viable cells was not accompanied by potassium release in either yeast, but zinc levels which affected viability in S. cerevisiae caused this yeast to release K +. No efflux of K + was observed for Spor. roseus despite its greater sensitivity to zinc.

Interactions of fungi with toxic metals

“…Furthermore, it should be stressed that inhibitor studies should be treated with caution since the enhancement of M^^ uptake in yeast induced by several plasma membrane ATPase inhibitors was due to increased cation permeability of the membrane rather than hyperpolarization (Borst-Pauwels, 1988). Similar conditions may apply to interactions of yeast with those metal cations or xenobiotics which are potentially toxic and induce K"^ effiux (Gadd & Mowll, 1983;Gadd, 1986a, c;Theuvenet et al, 1987;Borst-Pauwels, 1988;Belde et al, 1988). Divalent cation uptake, as measured in short-term experiments, is frequently accompanied by effiux of monovalent cations, usually K^, but H^ for Ca^^ and Mg^^ since uptake can be by means of the monovalent cation transport system.…”

“…Such observations also mean that measured net K"ê fflux from yeast cells exposed to xenobiotics is less than K^ efflux from the affected cells where an all-ornone process occurs (Borst-Pauwels, 1988). Assays where K^ release is used as an index of toxicity should therefore be cautiously interpreted and preferably in conjunction with alternative estimations of viability (Mowll & Gadd, 1983;BorstPauwels et al, 1983;Theuvenet et al, 1987;BorstPauwels, 1988). In addition, where a potentiallytoxic divalent cation induces K^ efflux by increasing membrane permeability, the uptake of other cations may be increased.…”

“…However, differences in accumulation may not be due to differences in affinities for the transport mechanism as some reductions in the net rate of Ca^"*^ and Sr""^ uptake, for example, may be due to increased leakage or effiux of these cations. In addition, depending on the metal and its concentration, there may be effects on the structural integrity of the membrane (Gadd & Mowll, 1983;White & Gadd, 1987 a). As with monovalent cations, uptake of divalent cations is inhibited or halted by metabolic inhibitors, low temperatures and the absence of energy-yielding substrates (Gadd & White, 1989 a;Sabie & Gadd, 1990;Starling & Ross, 1990).…”

“…However, tolerance may be related to decreased intracellular uptake and/or impermeability of the cells toward metal ions (Gadd, 1986a). A close connection between intracellular uptake and toxicity for Cu, Cd and Zn has been shown in 5. cerevisiae (Ross, 1977;Ross & Walsh, 1981;Gadd & Mowll, 1983;Mowll & Gadd, 1983;Joho e? a/., 1983Joho e?…”

Influence of Zinc on Distiller's Yeast: Cellular Accumulation of Zinc and Impact on Spirit Congeners

“…Yeast cells accumulate zinc biphasically 24 : the first phase consisting of a metabolism-independent zinc binding to sulphydryl residues within the cysteine groups of the cell wall 3 , and the second phase characterised by active transport of zinc inside the cell. Zinc is then subsequently translocated to the yeast vacuole 8,18,19,22 .…”