Tuesday, May 6, 2008 - 8:00 AM
7-01

Substrate Selective Uptake to Remove Acetate and Convert Sugar Mixtures

Mark A. Eiteman, Arun Lakshmanaswamy, Kevin C. Reilly, and Elliot Altman. Cmbe, University of Georgia, Driftmier, Athens, GA 30602

We report a new approach for selectively removing acetate from sugar mixtures, and then in a subsequent process step, for converting xylose and glucose simultaneously into products by fermentation. The process for converting sugar mixtures uses two “substrate-selective” strains, one unable to consume glucose and one unable to consume xylose. Using Escherichia coli as the model organism, the xylose-selective (glucose deficient) strain has mutations in the glk, ptsG and manZ genes while the glucose-selective (xylose deficient) strain has a mutation in the xylA gene. By combining these two strains in a single process, xylose and glucose are consumed more quickly than by a single-organism approach. The process for removing acetate selectively from acetate/xylose/glucose uses a single strain with all four mutations, thereby rendering this third strain unable to consume xylose or glucose. The ultimate two-step semi-continuous process—first acetate removal and then xylose/glucose conversion—has several advantages over other approaches. In particular, the process adapts to changing concentrations of any of these components, and the strategy results in the transformation of acetate into nutrients available to microbes in the second step. These results are discussed in the context of ethanol production, and the conversion of variable sugar feed streams.


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