Fermentative capacity in high-cell-density fed-batch cultures of baker's yeast.
High-cell-density fed-batch processes for bakers' yeast production will involve a low-average-specific growth rate due to the limited oxygen-transfer capacity of industrial bioreactors. The relationship between specific growth rate and fermentative capacity was investigated in aerobic, sucrose-limited fed-batch cultures of an industrial bakers' yeast strain. Using a defined mineral medium, biomass concentrations of 130 g dry weight/L were reproducibly attained. After an initial exponential-feed phase (mu = 0.18 h(-1)), oxygen-transfer limitation necessitated a gradual decrease of the specific growth rate to ca. 0.01 h(-1). Throughout fed-batch cultivation, sugar metabolism was fully respiratory, with a biomass yield of 0.5 g biomass/g sucrose(-1). Fermentative capacity (assayed off-line as ethanol production rate under anaerobic conditions with excess glucose) showed a strong positive correlation with specific growth rate. The fermentative capacity observed at the end of the process (mu = 0.01 h(-1)) was only half that observed during the exponential-feed phase (mu = 0.18 h(-1)). During fed-batch cultivation, activities of glycolytic enzymes, pyruvate decarboxylase and alcohol dehydrogenase in cell extracts did not exhibit marked changes. This suggests that changes of fermentative capacity during fed-batch cultivation were not primarily caused by regulation of the synthesis of glycolytic enzymes.
van Hoek
P
P
Kluyver Laboratory of Biotechnology, Delft University of Technology, Julianalaan 67, 2628 BC Delft, The Netherlands.
de Hulster
E
E
van Dijken
J P
JP
Pronk
J T
JT
D000426:Alcohol Dehydrogenase / Q000378:metabolism; D002455:Cell Division; D004798:Enzymes / Q000378:metabolism*; D005285:Fermentation; D011767:Pyruvate Decarboxylase / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000254:growth & development* / Q000378:metabolism*
D004798:Enzymes; D000426:Alcohol Dehydrogenase; D011767:Pyruvate Decarboxylase