Kj. Blackwell et al., MANGANESE TOXICITY TOWARDS SACCHAROMYCES-CEREVISIAE - DEPENDENCE ON INTRACELLULAR AND EXTRACELLULAR MAGNESIUM CONCENTRATIONS, Applied microbiology and biotechnology, 49(6), 1998, pp. 751-757
Inhibition of the growth of Saccharomyces cerevisiae was evident at co
ncentrations of 0.5 mM Mn2+ or higher, but a tolerance to lower Mn2+ c
oncentrations was observed. The inhibitory effects of 2.0 mM Mn2+ were
eliminated by supplementing the medium with excess Mg2+ (10 mM), wher
eas addition of excess Ca2+ and K+ had negligible effect on Mn2+ toxic
ity. Growth inhibition by Mn2+, in the absence of a Mg2+ supplement, w
as attributed to Mn2+ accumulation to toxic intracellular levels. Mn l
evels in S. cerevisiae grown in Mg2+-supplemented medium were severalf
old lower than those of cells growing in unsupplemented medium. Mn2+ t
oxicity 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
ME were more susceptible to Mn2+ toxicity than cells with high cellul
ar Mg, even when sequestered Mn2+ levels were similar. A critical Mg:M
n ratio of 2.0 was identified below which Mn2+ toxicity became acute.
The results demonstrate the importance of intracellular and extracellu
lar competitive interactions in determining the toxicity of Mn2+.