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Čertík, M., Jalčáková, M., Cirjak, M., Jandíková, J.

Department of Biochemical Technology, Faculty of Chemical and Food Technology, Slovak
University of Technology, Radlinského 9, 812 37 Bratislava, Slovak Republic.

The yeast biomass is a source of various useful compounds where lipids may represent one of
the valuable yeast products. Picha pastoris synthesizes several types of lipid structures.
Nonpolar lipids mainly consist of free sterols, free fatty acids, triacylglycerols and sterol
esters. Dominant polar lipids are characterized as phosphatidylcholine,
phosphatidylethanolamine and glycosylsterols. Ergosterol is the main fraction of total sterols,
minor sterols are composed from zymosterol, cholestadienol, ergostadieanol, ergostatetraenol,
fecosterol and lanosterol. Typical fatty acids are represented by palmitic, oleic, linoleic and
alpha-linolenic acids. Because biosynthesis of these compounds is affected by environmental
conditions, effect of various carbon substrates (glucose, glycerol, oleic acid, trioleine), their
concentrations, oxygen availability and temperature on lipogenesis of P. pastoris was studied.
It was found that increase in glucose or glycerol concentration in medium was accompanied
by accumulation of esterified sterols and phosphatidylcholine with concomitant reduction of
of triacylglycerols, free sterols and phosphatidylethanolamine. Addition of trioleine caused
elevation of triacylglycerols and glycosylsterol levels. Cultivation of P. pastoris with external
oleic acid inhibited biosynthesis of ergosterol, cholestadienol and zymosterol, but induced
biosynthesis of ergostatetraenol and fecosterol. It should be noted that addition of oleic acid to
a medium stimulated biosynthesis of linoleic and linolenic acids. It indicates that P. pastoris
possesses active Δ12/Δ15 desaturase system which effectively transforms extracellular fatty
acids to their unsaturated metabolites. Low oxygen availability resulted in declined amounts
of sterol esters and glycosylsterols with concomitant increase of free fatty acids, free sterols
and phosphatidylcholine. Decrease in temperature induced accumulation of both free sterols
and phosphatidylcholine, and reduced amount of glycosylsterols. Low temperature and
sufficient oxygen supply also stimulated biosynthesis of di- and triunsaturated fatty acids due
to activation of Δ12 and Δ15 desaturases. The work indicates that the rational physiological
regulation of lipid biosynthetic pathways in P. pastoris is useful tool for overproduction of
demanded compounds and might provide potential for both academic research and
commercial applications.

The work was supported by grant VEGA No. 1/0747/08 from the Grant Agency of Ministry
of Education, grants AVPP-0681-07 and VVCE-0064-07 from the Slovak Research and
Development Agency, Slovak Republic.

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