Chemical and cytological changes during the autolysis of yeasts

Cell suspensions of Sacharomyces cerevisiae, Kloeckera apiculata and Candida stellata were autolyzed in phosphate buffer, pH 4.5, for up to 10 days. Cell dry weights decreased by 25-35% after 10 days. Based on initial cell dry weight, the soluble autolysate consisted of: carbohydrate (principally polysaccharide) 3-7%; organic acids 3-6%; protein 12-13%; free amino acids 8-12%; nucleic acid products 3-5%; and lipids 1-2%. The main organic acids in autolysates were propionic, succinic and acetic and the main amino acids were phenylalanine, glutamic acid, leucine, alanine and arginine. Approximately 85-90% of cellular RNA and 25-40% of cellular DNA were degraded during autolysis. Both neutral lipid and phospholipid components were degraded, with neural lipids but not phospholipids being found in autolysates. Scanning and transmission electron micrographs showed retention of cell wall structure and shape during autolysis, but there was extensive intracellular disorganization within S. cerevisiae and C. stellata. There were differences in the autolytic behavior of K. apiculata compared with S. cerevisiae and C. stellata.