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Poster Presentation 3-26
Ethanol Production by Recombinant Yeast in a Starch-Fed Bioreactor
M. Mehmet Altintas, Betul Kirdar, Z. Ilsen Onsan, Stephen G. Oliver, and Kutlu O. Ulgen
Department of Chemical Engineering, University of Colorado Boulder, CO 80309-0424
Telephone: (303) 492-6530; Fax: (303) 492-4341; E-mail: altintas@colorado.edu
The production of ethanol from starch has been investigated in a recombinant Saccharomyces cerevisiae strain, YPB-G, which secretes a bifunctional fusion protein that contains Bacillus subtilis α-amylase and Aspergillus awamori glucoamylase activities. Initial glucose supply (4 g/L) was found to reduce batch-to-batch variations in glucoamylase activities and resulted in faster growth and high ethanol productivities. Starch was fed in a pulse manner or continuously over a certain period of time. In the latter strategy (intermittent feeding), starch was added at a constant flow rate in either equal or unequal sub-intervals. However, this feeding process yielded poor results in terms of both biomass and ethanol yields.
In the pulse-feeding experiments, the initial starch concentration differed between 0 and 50 g/L. Then, one, two or three successive feedings were done where their starch loads were adjusted according to the unconsumed starch in the bioreactor and fermentation time. Ethanol yields increased from 0.335 to 0.499 g ethanol/g substrate with decreasing initial starch concentrations from 50 to 10 g/L in pulse feeding experiments. The effects of a number of environmental factors on plasmid stability have been assessed in batch culture. These include initial glucose supply, colony selection methodology prior to inoculation, and medium formulation.
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