Metabolic state of Zymomonas mobilis in glucose-, fructose-, and xylose-fed continuous cultures as analysed by 13C- and 31P-NMR spectroscopy |
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Authors: | A A De Graaf Katharina Striegel Rolf M Wittig Birgit Laufer Günter Schmitz Wolfgang Wiechert Georg A Sprenger Hermann Sahm |
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Institution: | Institut für Biotechnologie I, Forschungszentrum Jülich, D-52425 Jülich, Germany e-mail: a.de.graaf@fz-juelich.de, Tel.: +49-2461-613969, Fax: +49-2461-612710, DE Alfred-Wegener-Institut für Polar- und Meeresforschung, Postfach 120161, D-27515 Bremerhaven, Germany, DE IMR, Abteilung Simulationstechnik, Universit?t Siegen, D-57068 Siegen, Germany, DE
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Abstract: | The reasons for the well-known significantly different behaviour of the anaerobic, gram-negative, ethanologenic bacterium
Zymomonas mobilis during growth on fructose (i.e. decreased growth and ethanol yields, increased by-product formation) as compared to that
on its second natural substrate, glucose, have remained unexplained. A xylose-fermenting recombinant strain of Z. mobilis that was recently constructed in our laboratory also unexpectedly displayed an increased formation of by-products and a strongly
reduced growth rate as compared to the parent strain. Therefore, a comprehensive study employing recently developed NMR-based
methods for the in vivo analysis of intracellular phosphorylated pool sizes and metabolic fluxes was undertaken to enable
a global characterization of the intracellular metabolic state of Z. mobilis during growth on 13C-labelled glucose, fructose and xylose in defined continuous cultures. The 13C-NMR flux analysis indicated that ribose 5-phosphate is synthesized via the nonoxidative pentose phosphate pathway in Z. mobilis, and it identified a metabolic bottleneck in the recombinant xylose-fermenting Z. mobilis strain at the level of heterologous xylulokinase. The 31P-NMR analyses revealed a global alteration of the levels of intracellular phosphorylated metabolites during growth on fructose
as compared to that on glucose. The results suggest that this is primarily caused by an elevated concentration of intracellular
fructose 6-phosphate.
Received: 7 January 1999 / Accepted: 22 March 1999 |
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Keywords: | Zymomonas mobilis Metabolic flux analysis Sugar phosphates Glucose Fructose Xylose 13C-NMR In vivo 31P-NMR Rate-limiting step |
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