Accumulation of Ag(I) by Saccharomyces cerevisiae Cells Expressing Plant Metallothioneins.

The various applications of Ag(I) generated the necessity to obtain Ag(I)-accumulating organisms for the removal of surplus Ag(I) from contaminated sites or for the concentration of Ag(I) from Ag(I)-poor environments. In this study we obtained Ag(I)-accumulating cells by expressing plant metallothioneins (MTs) in the model Saccharomyces cerevisiae. The cDNAs of seven Arabidopsis thaliana MTs (AtMT1a, AtMT1c, AtMT2a, AtMT2b, AtMT3, AtMT4a and AtMT4b) and four Noccaea caerulescens MTs (NcMT1, NcMT2a, NcMT2b and NcMT3) fused to myrGFP displaying an N-terminal myristoylation sequence for plasma membrane targeting were expressed in S. cerevisiae and checked for Ag(I)-related phenotype. The transgenic yeast cells were grown in copper-deficient media to ensure the expression of the plasma membrane high-affinity Cu(I) transporter Ctr1, and also to elude the copper-related inhibition of Ag(I) transport into the cell. All plant MTs expressed in S. cerevisiae conferred Ag(I) tolerance to the yeast cells. Among them, myrGFP-NcMT3 afforded Ag(I) accumulation under high concentration (10⁻50 µM), while myrGFP-AtMT1a conferred increased accumulation capacity under low (1 µM) or even trace Ag(I) (0.02⁻0.05 µM). The ability to tolerate high concentrations of Ag(I) coupled with accumulative characteristics and robust growth showed by some of the transgenic yeasts highlighted the potential of these strains for biotechnology applications.

Interaction between lanthanide ions and Saccharomyces cerevisiae cells.

Lanthanides are a group of non-essential elements with important imaging and therapeutic applications. Although trivalent lanthanide ions (Ln³âº) are used as potent blockers of Ca²âº channels, the systematic studies correlating Ln³âº accumulation and toxicity to Ca²âº channel blocking activity are scarce. In this study, we made use of the eukaryotic model Saccharomyces cerevisiae to investigate the correlation between Ln³âº accumulation, their toxicity and their capacity to block the exogenous stress-induced Ca²âº influx into the cytosol. It was found that the Ln³âº blocked the Ca²âº entry into the yeast cells only when present at concentration high enough to allow rapid binding to cell surface. At lower concentrations, Ln³âº were taken up by the cell, but Ca²âº blockage was no longer achieved. At 1 mM concentration, all ions from the Ln³âº series could block Ca²âº entry into cytosol with the exception of La³âº, and to a lesser extent, Pr³âº and Nd³âº. The plasma membrane Ca²âº-channel Cch1/Mid1 contributed to La³âº and Gd³âº entry into the cells, with a significant preference for La³âº. The results open the possibility to obtain cells loaded with controlled amounts and ratios of Ln³âº.

Calcium signaling mediates the response to cadmium toxicity in Saccharomyces cerevisiae cells.

The involvement of Ca(2+) in the response to high Mn(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), and Hg(2+) was investigated in Saccharomyces cerevisiae. The yeast cells responded through a sharp increase in cytosolic Ca(2+) when exposed to Cd(2+), and to a lesser extent to Cu(2+), but not to Mn(2+), Co(2+), Ni(2+), Zn(2+), or Hg(2+). The response to high Cd(2+) depended mainly on external Ca(2+) (transported through the Cch1p/Mid1p channel) but also on vacuolar Ca(2+) (released into the cytosol through the Yvc1p channel). The adaptation to high Cd(2+) was influenced by perturbations in Ca(2+) homeostasis. Thus, the tolerance to Cd(2+) often correlated with sharp Cd(2+)-induced cytosolic Ca(2+) pulses, while the Cd(2+) sensitivity was accompanied by the incapacity to rapidly restore the low cytosolic Ca(2+).

Vaccinium corymbosum L. (blueberry) extracts exhibit protective action against cadmium toxicity in Saccharomyces cerevisiae cells.

Blueberries (Vaccinium corymbosum L.) are a rich source of antioxidants and their consumption is believed to contribute to food-related protection against oxidative stress. In the present study, the chemoprotective action of blueberry extracts against cadmium toxicity was investigated using a cadmium-hypersensitive strain of Saccharomyces cerevisiae. Four varieties of blueberries were used in the study, and it was found that the extracts with high content of total anthocyanidins exhibited significant protective effect against the toxicity of cadmium and H2O2. Both the blueberry extracts and pure cyanidin exhibited protective effects against cadmium in a dose-dependent manner, but without significantly interfering with the cadmium accumulation by the yeast cells. The results imply that the blueberry extracts might be a potentially valuable food supplement for individuals exposed to high cadmium.