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Dioctyl phthalate increases the percentage of unsaturated fatty acids with a concomitant decrease in cellular heat shock sensitivity in the yeast Saccharomyces cerevisiae

School of Biological Sciences, Queen Mary and Westfield College, Mile End Road, London E1 4NS, UK¹

Author for correspondence: Brendan P. G. Curran. Tel: +44 207 775 3013. Fax: +44 208 983 0973. e-mail: B.Curran{at}qmw.ac.uk

In the past it has been reproducibly demonstrated that 37 °C-grown DBY747 yeast cells have 29% more unsaturated fatty acids and a 3 °C higher maximal heat shock response (HSR) than their 25 °C counterparts. Suddenly the HSR and lipid profiles of cells grown at 25 °C and 37 °C became indistinguishable from one another. This paper reports an aberrantly high level of unsaturated fatty acids and an abnormally insensitive HSR in cells grown at 25 °C in yeast nitrogen base (YNB) that has been reconstituted from dehydrated medium packaged in ’new’ plastic containers. Effective even at a 1:600 dilution of reconstituted medium in laboratory-made YNB, the ’active ingredient’ was identified using a combination of HPLC and mass spectroscopy as dioctyl phthalate (a plasticising agent). Furthermore, the same levels of increase in the percentage of unsaturated fatty acids and decrease in the sensitivity of HSR were found in cells grown in laboratory-made YNB that contained as little as 36 µM pure dioctyl phthalate. This compound nevertheless failed to elicit an observable effect on cellular growth rate at levels up to and including 144 µM. These results suggest that dioctyl phthalate causes yeast cells to accumulate high levels of unsaturated fatty acids with a concomitant decrease in the sensitivity of the HSR, without compromising overall cellular function. They also support earlier work that suggested that the HSR is exquisitely sensitive to the level of unsaturated fatty acids present in yeast cells.

Keywords: Dioctyl phthalate, lipids, yeast, heat shock response

Abbreviations: HSE, heat shock element; HSR, heat shock response