ENERGY-METABOLISM IN THE THERMOPHILIC YEAST CANDIDA-BLANKII

The energy metabolism of the true thermotolerant yeast Candida blankii was investigated using a strain that cannot grow at temperatures belo w 28 degrees C or above 43-45 degrees C. When grown at temperatures be tween 30 and 45 degrees C, C. blankii cells utilized both fermentable and nonfermentable substrates. In cells grown in the presence of gluco se, sucrose, succinate, and octadecane (a soluble paraffin), the respi ration rate depended on the growth phase, reaching its highest at the phase of exponential growth. During the exponential growth phase, cell s showed no activity of the alternative terminal oxidase. However, dur ing stationary growth, the electron flow was distributed between two t erminal oxidases, i.e., cytochrome oxidase and the alternative oxidase . In C. blankii cells grown in the presence of octadecane, succinate, or low concentrations of glucose (0.5%), oxidative phosphorylation pla yed the leading role in the energy balance of the cells. The mitochond ria isolated from cells grown at 43 degrees C in media with sucrose or succinate as a carbon source remained physiologically intact and reta ined the activity of all three coupling points in the respiratory chai n. It is concluded that the temperature of 43 degrees C falls in the r egion where mitochondria are fully competent in oxidative phosphorylat ion.