INCREASED CELLULAR FATTY-ACID DESATURATION AS A POSSIBLE KEY FACTOR IN THERMOTOLERANCE IN SACCHAROMYCES-CEREVISIAE

An increase of the unsaturation level of the cellular fatty acids was observed at sublethal or superoptimal temperatures in Saccharomyces ce revisiae. The hypothesis of this paper is that a high unsaturated fatt y acids relative content ''per se'' is not a prerequisite for withstan ding sublethal temperature stress in yeast but is the result of oxygen -consuming desaturase activation, with consequent reduction of oxygen and the oxygen free radicals as they form during thermal stress. In th e thermotolerant strains, no increase of cellular thiobarbituric acid reactive substances (TBARSs) was observed when temperature approached the maximal growth temperature, suggesting prevention of oxidative dam age. On the other hand, the values of TBARSs tripled at 42 degrees C i n nonthermotolerant strains. When a sublethal hydrogen peroxide treatm ent preceded a rapid temperature rise, a selected thermotolerant strai n responded with a relative increase of saturated fatty acids. This re sponse, associated with an insignificant viability loss due to the dou ble stress, suggests the induction an alternative oxygen consumption m echanism preventing excessive fatty acid unsaturation, which could be detrimental to the cells in the presence of hydrogen peroxide at suble thal temperatures.