Chemostat study of xylitol production by Candida guilliermondii |
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Authors: | T Granström H Ojamo M Leisola |
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Institution: | (1) Helsinki University of Technology, Laboratory of Bioprocess Engineering, POB 6100, FIN-02015 HUT, Finland e-mail: tom.granstrom@hut.fi Tel.: +358-0-4512560 Fax: +358-0-462373, FI;(2) Danisco Sugar & Sweetener Development, Kantvik, FIN-0246, Finland, FI |
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Abstract: | The mechanism of production of xylitol from xylose by Candida guilliermondii was studied using chemostat cultures and enzymatic assays. The maximum dilution rate in aerobic conditions was 0.34 1/h.
No xylitol was produced. Under oxygen-limited conditions xylose uptake was impaired and glycerol accumulated but no xylitol
was detected. Under transient oxygen limitation, caused by a gradual decrease in the agitation rate, onset of xylitol, acetate
and residual xylose accumulation occurred simultaneously when q
O2 dropped below 25 mmol/C-mmol cell dry weight (CDW) per hour. Ethanol and glycerol started to accumulate when q
O2 dropped below 20 mmol/C-mmol CDW per hour. The highest in vitro enzyme activities were found at the lowest dilution rate
studied (0.091/h) under aerobic conditions. The amount of active enzymes or cofactor availability did not limit the rate of
xylose consumption. Our results confirm that a surplus of NADH during transient oxygen limitation inhibited the activity of
xylitol dehydrogenase which resulted in xylitol accumulation. Phosphoglucoisomerase (E.C. 5.3.1.9.) and glucose-6-phosphate
dehydrogenase (E.C. 1.1.1.49) activities suggest re-shuttling of the metabolites into the pentose phosphate pathway.
Received: 7 March 2000 / Received revision: 9 June 2000 / Accepted: 18 June 2000 |
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