CONTINUOUS CULTIVATION OF BAKERS-YEAST - CHANGE IN CELL COMPOSITION AT DIFFERENT DILUTION RATES AND EFFECT OF HEAT-STRESS ON TREHALOSE LEVEL

The cell composition of bakers' yeast in a continuous culture was dete rmined for different dilution rates. Also, the cellular response to he at stress in terms of trehalose, RNA, glycogen and protein was determi ned at a specified dilution rate of 0.1/h. The amount of storage sacch arides, trehalose and glycogen, was found to decrease whereas the amou nt of RNA and protein increased with increasing dilution rates. As the dilution rate was increased from 0.1 to 0.4/h at 0.05 intervals the s teady-state trehalose content decreased from 33 to 8.6 mg/g biomass, a nd glycogen content from 150 to 93 mg/g biomass. On the other hand, th e protein content increased from 420 to 530 mg/g biomass and the RNA c ontent from 93 to 113 mg/g biomass. Heat stress was applied by increas ing the medium temperature from 30 to 36, 38 or 40 degrees C at consta nt dilution rates. The highest amount of trehalose accumulation, 108 m g/g biomass, was achieved when heat stress at 38 degrees C was applied . The protein content, on the other hand, decreased from 350 to 325 mg /g biomass at the end of the experiment.