Abstract
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.
Highlights
Contamination with heavy metals represents a world-wide concern constantly prompting the necessity to develop cost-effective eco-friendly technologies for the remediation of polluted sites [1]
Cells 2018, 7, 266 we found that Saccharomyces cerevisiae cells expressing plant metallothioneins (MTs) targeted to the cytosolic face of the plasma membrane accumulate divalent metal cations such as Cd(II), Co(II), Cu(II), Mn(II), or Ni(II) [10]
If heterologous MTs are anchored to the inner face of plasma membrane, it is expected that they would act as a buffer against the toxic Ag(I) ions which enter the cell
Summary
Contamination with heavy metals represents a world-wide concern constantly prompting the necessity to develop cost-effective eco-friendly technologies for the remediation of polluted sites [1]. Silver is highly toxic especially in aquatic environments [2], where silver in all forms—free cationic Ag(I), colloidal or nanoparticles (AgNP)—exerts deleterious effects towards living organisms [2,3]. Numerous studies emphasized the need to develop biotechnologies for the remediation of environmental matrices contaminated by heavy metals. In this context, engineered yeasts have biotechnological potential for metal removal and/or recovery [5,6,7,8,9].
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