Continuous culture studies of xylose-fermentingZymomonas mobilis |
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Authors: | Lawford Hugh G Rousseau Joyce D Mohagheghi Ali McMillan James D |
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Institution: | (1) Bioengineering Laboratory, Department of Biochemistry, University of Toronto, M5S 1A8, Toronto, Ontario, Canada;(2) Biotechnology Center for Fuels andChemicals, National Renewable Energy Laboratory, 1617Cole Boulevard, 80401 Golden, CO |
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Abstract: | The continuous cofermentation performance of xylose-fermentingZymomonas mobilis at 30°C and pH 5.5 was characterized using a pure-sugar feed solution that contained 8 g/L glucose and 40 g/L xylose. Successful
chemostat start up resulted in complete utilization of glucose and greater than 85% utilization of xylose, but was only reproducibly
achieved using initial dilution rates at or less than 0.04/h; once initiated, cofermentation could be maintained at dilution
rates of 0.04 to 0.10/h. Whereas xylose and cell-mass concentrations increased gradually with increasing dilution rate, ethanol
concentrations and ethanol yields on available sugars remained approximately constant at 20–22 g/L and 80–90% of theoretical,
respectively. Volumetric and specific ethanol productivities increased linearly with increasing dilution rate, rising from
approx 1.0 each (g/L/h or g/g/h) at a dilution rate of 0.04/h to approx 2.0 each (g/L/h or g/g/h) at a dilution rate of 0.10/h.
Similarly, specific sugar-utilization rates increased from approx 2.0 g/g/h at dilution rate 0.04/h to approx 3.5 g/g/h at
dilution rate of 0.10/h. The estimated values of 0.042 g/g for the maximum Z.mobilis cell-mass yield on substrate and 1.13 g/g/h for the minimum specific substrate utilization rate required for cellular maintenance
energy are within the range of values reported in the literature. Results are also presented which suggest that long-term
adaptation in continuous culture is a powerful technique for developing strains with higher tolerance to inhibitory hemicellulose
hydrolyzates. |
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Keywords: | Index Entries" target="_blank">Index Entries Adaptation continuous cofermentation ethanol xylose Zymomonas mobilis |
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