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Appl Environ Microbiol. 1990 November; 56(11): 3389-3394
Copyright © 1990, American Society for Microbiology. All Rights Reserved.

Effect of Oxygenation on Xylose Fermentation by Pichia stipitis

Kerstin Skoog* and Bärbel Hahn-Hägerdal

Applied Microbiology, Chemical Center, P.O. Box 124, S-221 00 Lund, Sweden

ABSTRACT

The effect of oxygen limitation on xylose fermentation by Pichia stipitis (CBS 6054) was investigated in continuous culture. The maximum specific ethanol productivity (0.20 g of ethanol g dry weight–1 h–1) and ethanol yield (0.48 g/g) was reached at an oxygen transfer rate below 1 mmol/liter per h. In the studied range of oxygenation, the xylose reductase (EC 1.1.1.21) and xylitol dehydrogenase (EC 1.1.1.9) activities were constant as well as the ratio between the NADPH and NADH activities of xylose reductase. No xylitol production was found. The pyruvate decarboxylase (EC 4.1.1.1) activity increased and the malate dehydrogenase (EC 1.1.1.37) activity decreased with decreasing oxygenation. With decreasing oxygenation, the intracellular intermediary metabolites sedoheptulose 7-phosphate, glucose 6-phosphate, fructose 1,6-diphosphate, and malate accumulated slightly while pyruvate decreased. The ratio of the xylose uptake rate under aerobic conditions, in contrast to that under anaerobic assay conditions, increased with increasing oxygenation in the culture. The results are discussed in relation to the energy level in the cell, the redox balance, and the mitochondrial function.


FOOTNOTES

* Corresponding author.


Appl Environ Microbiol. 1990 November; 56(11): 3389-3394
Copyright © 1990, American Society for Microbiology. All Rights Reserved.




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Copyright © 1990 by the American Society for Microbiology. All rights reserved.