Kinetic evaluation of recombinant strains of Zymomonas mobilis for ethanol production from glucose/xylose media
2000
Garcia, P. | Jaochimsthal, E. | Rogers, P.I. (University of New South Wales, Sydney (Australia))
The fermentation characteristics of two recombinant strains of Zymomonas mobilis CP4 (pZB5) and ZM4 (pZB5), capable of converting both glucose and xylose to ethanol, have been characterized in batch culture studies. The specific growth rate and specific ethanol production on combined sugars were greater than those observed on xylose alone. The overall biomass yields were in the range of 0.02-0.03 g/g and were higher for combined sugars than for xylose alone. Xylose was used at a much slower rate than glucose, and only after glucose was nearly depleted. Ethanol yields were similar for each of the fermentations: 0.46-0.47 g/g or 90-92% of the maximum theoretical yield. The strain ZM4 (pZB5) was found to be capable of converting a mixture of 65 g/L glucose and 65 g/L xylose to more than 60 g/L ethanol in 48 h. Higher sugar concentrations resulted in incomplete xylose utilization after 80 h presumably due to ethanol inhibition of xylose assimilation or metabolism. A comparative evaluation indicates that ZM4 (pZB5) is very competitive with other recombinant bacteria and yeast which are able to convert xylose to ethanol
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