Manganese toxicity towards Saccharomyces cerevisiae: dependence on intracellular and extracellular magnesium concentrations.
Inhibition of the growth of Saccharomyces cerevisiae was evident at concentrations of 0.5 mM Mn2+ or higher, but a tolerance to lower Mn2+ concentrations was observed. The inhibitory effects of 2.0 mM Mn2+ were eliminated by supplementing the medium with excess Mg2+ (10 mM), whereas addition of excess Ca2+ and K+ had negligible effect on Mn2+ toxicity. Growth inhibition by Mn2+, in the absence of a Mg2+ supplement, was attributed to Mn2+ accumulation to toxic intracellular levels. Mn levels in S. cerevisiae grown in Mg(2+)-supplemented medium were severalfold lower than those of cells growing in unsupplemented medium. Mn2+ toxicity was also influenced by intracellular Mg, as Mn2+ toxicity was found to be more closely correlated with the cellular Mg:Mn ratio than with cellular Mn levels alone. Cells with low intracellular levels of Mg were more susceptible to Mn2+ toxicity than cells with high cellular Mg, even when sequestered Mn2+ levels were similar. A critical Mg:Mn ratio of 2.0 was identified below which Mn2+ toxicity became acute. The results demonstrate the importance of intracellular and extracellular competitive interactions in determining the toxicity of Mn2+.
Blackwell
K J
KJ
School of Biological Sciences, Dublin City University, Dublin 9, Ireland.
Tobin
J M
JM
Avery
S V
SV
D002118:Calcium / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D008274:Magnesium / Q000378:metabolism* / Q000494:pharmacology; D008345:Manganese / Q000378:metabolism / Q000494:pharmacology*; D011188:Potassium / Q000494:pharmacology; D012441:Saccharomyces cerevisiae / Q000187:drug effects* / Q000254:growth & development / Q000378:metabolism; D013997:Time Factors
D008345:Manganese; D008274:Magnesium; D011188:Potassium; D002118:Calcium