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Appl. Environ. Microbiol., Nov 1996, 3960-3966, Vol 62, No. 11
SV Avery, NG Howlett and S Radice
One major mechanism of copper toxicity towards microorganisms is disruption
of plasma membrane integrity. In this study, the influence of plasma
membrane fatty acid composition on the susceptibility of Saccharomyces
cerevisiae to Cu2+ toxicity was investigated. Microbial fatty acid
composition is highly variable, depending on both intrinsic and
environmental factors. Manipulation was achieved in this study by growth in
fatty acid-supplemented medium. Whereas cells grown under standard
conditions contained only saturated and monounsaturated fatty acids,
considerable incorporation of the diunsaturated fatty acid linoleate (18:2)
(to more than 65% of the total fatty acids) was observed in both whole-cell
homogenates and plasma membrane-enriched fractions from cells grown in
linoleate-supplemented medium. Linoleate enrichment had no discernible
effect on the growth of S. cerevisiae. However, linoleate-enriched cells
were markedly more susceptible to copper-induced plasma membrane
permeabilization. Thus, after addition of Cu(NO3)2, rates of cellular K+
release (loss of membrane integrity) were at least twofold higher from
linoleate-supplemented cells than from unsupplemented cells; this
difference increased with reductions in the Cu2+ concentration supplied.
Levels of cellular Cu accumulation were also higher in
linoleate-supplemented cells. These results were correlated with a very
marked dependence of whole-cell Cu2+ toxicity on cellular fatty acid
unsaturation. For example, within 10 min of exposure to 5 microM Cu2+, only
3% of linoleate-enriched cells remained viable (capable of colony
formation). In contrast, 100% viability was maintained in cells previously
grown in the absence of a fatty acid supplement. Cells displaying
intermediate levels of linoleate incorporation showed intermediate Cu2+
sensitivity, while cells enriched with the triunsaturated fatty acid
linolenate (18:3) were most sensitive to Cu2+. These results demonstrate
for the first time that changes in cellular and plasma membrane fatty acid
compositions can dramatically alter microbial sensitivity to copper.
Copyright © 1996, American Society for Microbiology
Copper toxicity towards Saccharomyces cerevisiae: dependence on plasma membrane fatty acid composition
School of Biological and Molecular Sciences, Oxford Brookes University, Headington, United Kingdom.
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