EFFECTS OF GROWTH-CONDITIONS ON MITOCHONDRIAL MORPHOLOGY IN SACCHAROMYCES-CEREVISIAE

Effects of growth conditions on mitochondrial morphology were studied in living Saccharomyces cerevisiae cells by vital staining with the fl uorescent dye dimethyl-aminostyryl-methylpyridinium iodine (DASPMI), f luorescence microscopy, and confocal-scanning laser microscopy. Cells from respiratory, ethanol-grown batch cultures contained a large numbe r of small mitochondria. Conversely, cells from glucose-grown batch cu ltures, in which metabolism was respiro-fermentative, contained small numbers of large, branched mitochondria. These changes did not signifi cantly affect the fraction of the cellular volume occupied by the mito chondria. Similar differences in mitochondrial morphology were observe d in glucose-limited chemostat cultures. In aerobic chemostat cultures , glucose metabolism was strictly respiratory and cells contained a la rge number of small mitochondria. Anaerobic, fermentative chemostat cu ltivation resulted in the large, branched mitochondrial structures als o seen in glucose-grown batch cultures. Upon aeration of a previously anaerobic chemostat culture, the maximum respiratory capacity increase d from 10 to 70 mu mole.min(-1).g dry weight(-1) within 10 h. This tra nsition resulted in drastic changes of mitochondiral number, morpholog y and, consequently, mitochondrial surface area. These changes continu ed for several hours after the respiratory capacity had reached its ma ximum. Cyanide-insensitive oxygen consumption contributed ca. 50% of t he total respiratory capacity in anaerobic cultures, but was virtually absent in aerobic cultures. The response of aerobic cultures to oxyge n deprivation was qualitatively the reverse of the response of anaerob ic cultures to aeration. The results indicate that mitochondrial morph ology in S. cerevisiae is closely linked to the metabolic activity of this yeast: conditions that result in repression of respiratory enzyme s generally lead to the mitochondrial morphology observed in anaerobic ally grown, fermenting cells.