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Growth characteristics and metabolic flux analysis of Candida milleri
Author(s) -
Granström Tom B.,
Aristidou Aristos A.,
Jokela Jouni,
Leisola Matti
Publication year - 2000
Publication title -
biotechnology and bioengineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.136
H-Index - 189
eISSN - 1097-0290
pISSN - 0006-3592
DOI - 10.1002/1097-0290(20001020)70:2<197::aid-bit9>3.0.co;2-d
Subject(s) - xylose , biochemistry , xylitol , chemistry , metabolite , chemostat , xylose metabolism , dehydrogenase , flux (metallurgy) , acetaldehyde , enzyme , fermentation , biology , ethanol , bacteria , organic chemistry , genetics
The growth characteristics of the sourdough yeast Candida milleri was studied in a carbon‐limited aerobic chemostat culture on defined medium. The effect of glucose, xylose, and glucose–xylose mixture on metabolite production and on key enzyme activities was evaluated. Xylose as a sole carbon source was not metabolized by C. milleri . Glucose as a sole carbon source produced only biomass and carbon dioxide. When a glucose–xylose mixture (125:125 C‐mM) was used as a carbon source, a small amount of xylose was consumed and a low concentration of xylitol was produced (7.20 C‐mM). Enzymatic assays indicated that C. milleri does not possess xylitol dehydrogenase activity and its xylose reductase is exclusively NADPH‐dependent. In glucose medium both NAD + ‐ and NADP + ‐dependent aldehyde dehydrogenase activities were found, whereas in a glucose–xylose medium only NADP + ‐dependent aldehyde dehydrogenase activity was detected. The developed metabolic flux analysis corresponded well with the experimentally measured values of metabolite production, oxygen consumption (OUR), and carbon dioxide production (CER). Turnover number in generation and consumption of ATP, mitochondrial and cytosolic NADH, and cytosolic NADPH could be calculated and redox balance was achieved. Constraints were imposed on the flux estimates such that the directionality of irreversible reactions is not violated, and cofactor dependence of the measured enzyme activities were taken into account in constructing the metabolic flux network. © 2000 John Wiley & Sons, Inc. Biotechnol Bioeng 70: 197–207, 2000.