Saccharomyces cerevisiae was cultivated in the presence of cis-9,trans-11 or trans-10,cis-12 isomers of free conjugated linoleic acid (CLA), and the effects of the isomers on the regioisomerisms of triacylglycerol (TAG) of the yeast were elucidated. Both isomers constituted about 34% of all fatty acids and increased drastically the number of different TAG species. Nearly all of the species contained CLA in at least one sn-position. In the most abundant species analyzed (20% of total species), the cis-9,trans-11 isomer appeared in combination with monounsaturated fatty acids (C16:1, C:18:1) whereas trans-10,cis-12 isomer was most frequently present with a medium chain fatty acid (C10:0 or C12:0) in the sn-2 position and C16:0 in one of the end positions (14% of total species). With either isomer, the amount of TAG species in which CLA encompassed all sn-positions was ca. 4%. Thus, S. cerevisiae can be used to produce edible single cell oil characterized by very heterogeneous distribution of CLA among the different TAG species.

The yeast Saccharomyces cerevisiae was cultivated in the presence of free CLA that was either a pure trans-10,cis-12 isomer, a pure cis-9,trans-11 isomer, or a 1:1 mixture of the two, and the influence of these supplementations on the content and FA composition of the lipids in the yeast was determined. Neither the pure isomers nor their 1:1 mixture influenced the growth of the yeast, but the trans-10,cis-12 isomer reduced the amount of cellular lipids by 40%. The reduction in total cellular lipids by the trans-10,cis-12 CLA was due to a reduction in TAG. Both of the isomers were incorporated into the yeast lipids, reaching a proportion of about 33% in TAG. With the incorporation of CLA, the yeast reduced the amount and desaturation of endogenously synthesized FA. These clear and pronounced isomer-specific effects of CLA on the yeast suggest that yeast might be a useful model to obtain a more comprehensive view of the mechanisms of the action of CLA on lipid metabolism.Conjugated isomers of linoleic acid (CLA) have been reported to reduce adiposity in animals and humans (reviewed in Ref. 1), and trans-10,cis-12 CLA has been shown to be responsible for this antilipogenic effect. In particular, the amount of TAG has decreased when a diet containing trans-10,cis-12 CLA has been fed to test animals or humans. On the basis of numerous in vivo and in vitro studies, several hypotheses for this mechanism have emerged. The suggestions with the most support are modifications of the activity of enzymes essential in FA uptake and metabolism, increased energy expenditure, and decreased preadipocyte differentiation and proliferation (reviewed in Refs. 1 and 2). However, the exact mechanism of the fat or TAG reduction remains to be elucidated. Considering the effects of CLA isomers on mammalian metabolism, the results of studies carried out by different laboratories are somewhat conflicting. The effects of CLA on animal metabolism seem to be more or less isomer, dose, time, and species specific.The yeast Saccharomyces cerevisiae has been a useful model to understand the synthesis of eukaryotic TAG and its role in various cell processes (3). During growth, S. cerevisiae is able to incorporate free long-chain FA from the culture medium and accumulate them without modification in TAG and, as a result, the cellular lipid content is increased (4). Therefore, the FA composition of TAG resembles the FA composition of the growth environment of the yeast. TAG are used as an energy reserves and sources of FA for the synthesis of membrane phospholipids (5,6). All the acquired FA are not necessarily suitable for use in membrane synthesis. Thus, the third function of TAG is to serve as a storage place for such FA (7).However, less is known about how the yeast lipids are affected when the culture medium is supplemented with CLA, which is known to inhibit the development of adipose tissue in mammals. Elucidation of the effects of CLA on yeast lipids could reveal the potential of yeast as a model organism in CLA studies. Therefore, a study was...