17-21: Pseudo-continuous fermentation - an effective way to study the dynamics of co-culture systems

Tuesday, May 1, 2012
Napoleon Ballroom C-D, 3rd fl (Sheraton New Orleans)
Min Hea Kim1, Meng Liang1, Qinghua He2 and Jin Wang1, (1)Department of Chemical Engineering, Auburn University, Auburn, AL, (2)Department of Chemical Engineering, Tuskegee University, Tuskegee, AL
The use of renewable resources, such as lignocellulosic biomasses, to produce ethanol offers environmental and economical benefits over fossil fuel. Economical production of ethanol from lignocellulosic hydrolysate requires efficient utilization of both glucose and xylose.

Existing research has shown that, besides recombinant strategy, co-culture is a promising way to ferment mixed glucose and xylose for ethanol production, especially in reducing fermentation time and improving ethanol productivity. However, there is a lack of systematic study on the dynamic properties of co-culture systems. In addition, major challenges associated with xylose fermentation, such as the diauxic growth and low ethanol tolerance of the xylose fermenting strain, have not been fully addressed. Therefore, new approaches are needed to help understand and explore the potential of the co-culture strategy.

In this work, we study the co-culture system consisting of Saccharomyces cerevisiae and Pichia stipitis. Specifically, we have developed a novel bioreactor to enable different fermentative conditions, such as oxygen transfer rate, for different strains. The bioreactor also enables pseudo-continuous fermentation, i.e. continuous fermentation with cell retention, to prevent cell washout. In this study, we show that with the developed bioreactor, we were able to achieve simultaneous complete consumption of both glucose and xylose. Furthermore, we show that pseudo-continuous operation provides ideal environment for cell adaptation, evidenced by the significantly improved ethanol tolerance of both strains.

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