title: Influence of silicon on cobalt, zinc, and magnesium in baker's yeast, Saccharomyces cerevisiae.
abstract: Silicon (Si, as silicate) is involved in numerous important structure and function roles in a wide range of organisms, including man. Silicate availability influences metal concentrations within various cell and tissue types, but, as yet, clear mechanisms for such an influence have been discovered only within the diatoms and sponges. In this study, the influence of silicate on the intracellular accumulation of metals was investigated in baker's yeast (Saccharomyces cerevisiae). It was found that at concentrations up to 10 mM, silicate did not influence the growth rate of S. cerevisiae within a standard complete medium. However, an 11% growth inhibition was observed when silicate was present at 100 mM. Intracellular metal concentrations were investigated in yeast cultures grown without added silicate (-Si) or with the addition of 10 mM silicate (+Si). Decreased amounts of Co (52%), Mn (35%), and Fe (20%) were found within +Sigrown yeast cultures as compared to -Si-grown ones, whereas increased amounts of Mo (56%) and Mg (38%) were found. The amounts of Zn and K were apparently unaffected by the presence of silicon. +Si enhanced the yeast growth rate for low-Zn2+ medium, but it decreased the growth rate under conditions of a low Mg2+ medium and did not alter the growth rates in high Zn2+ and Co2+ media. +Si doubled the uptake rate of Co2+ but did not influence that of Zn2+. We propose that a possible explanation for these results is that polysilicate formation at the cell wall changes the cell wall binding capacity for metal ions. The toxicity of silicate was compared to germanium (Ge, as GeO2), a member of the same group of elements as Si (group 14). Hence, Si and Ge are chemically similar, but silicate starts to polymerize to oligomers above 5 mM, whereas Ge salts remain as monomers at such concentrations. Ge proved to be far more toxic to yeast than Si and no influence of Si on Ge toxicity was found. We propose that these results relate to differences in cellular uptake.
authors.affiliation: Faculty of Applied Sciences, Department of Radiation, Radionuclides & Reactors, Delft University of Technology, Mekelweg 15, 2629 JB Delft, The Netherlands.
authors.forename: H J
authors.initials: HJ
authors.lastname: Brasser
authors.forename: G C
authors.initials: GC
authors.lastname: Krijger
authors.forename: T G
authors.initials: TG
authors.lastname: van Meerten
authors.forename: H T
authors.initials: HT
authors.lastname: Wolterbeek
mesh_terms: D003035:Cobalt / Q000378:metabolism*; D003470:Culture Media; D005857:Germanium / Q000494:pharmacology; D008274:Magnesium / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000254:growth & development / Q000378:metabolism*; D012825:Silicon / Q000494:pharmacology*; D015032:Zinc / Q000378:metabolism*
chemical_list: D003470:Culture Media; D005857:Germanium; D003035:Cobalt; D008274:Magnesium; D015032:Zinc; D012825:Silicon