Abstract
We report a new approach for the simultaneous conversion of xylose and glucose sugar mixtures into products by fermentation. The process simultaneously uses two substrate-selective strains of Escherichia coli, one which is unable to consume glucose and one which is unable to consume xylose. The xylose-selective (glucose deficient) strain E. coli ZSC113 has mutations in the glk, ptsG and manZ genes while the glucose-selective (xylose deficient) strain E. coli ALS1008 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. Moreover, we demonstrate that the process is able to adapt to changing concentrations of these two sugars, and therefore holds promise for the conversion of variable sugar feed streams, such as lignocellulosic hydrolysates.
Highlights
The efficient and simultaneous conversion of pentoses and hexoses is a significant hurdle to the economic utilization of biomass hydrolysates for the generation of any fermentation product
The inability of microorganisms to utilize xylose effectively is most commonly associated with fuel ethanol production, the formation of other fermentation products from sugar mixtures could benefit from a strategy to use both sugars effectively
The xyloseselective strain ZSC113 has mutations in the three genes involved in glucose uptake [12], rendering it unable to consume glucose: ptsG codes for the Enzyme IICBGlc of the phosphotransferase system (PTS) for carbohydrate transport [13], manZ codes for the IIDMan domain of the mannose PTS permease [14], glk codes for glucokinase [12]
Summary
The efficient and simultaneous conversion of pentoses and hexoses is a significant hurdle to the economic utilization of biomass hydrolysates for the generation of any fermentation product. The central problem is that either the desired microorganism consumes this sugar mixture sequentially (e.g. first glucose and xylose) or the organism is unable to utilize the pentose at all (e.g. Saccharomyces cerevisiae). One strategy has been to introduce genes involved in xylose consumption into an organism which does not natively have this ability but can generate a desirable product. It does not naturally consume xylose, the common yeast Saccharomyces cerevisiae is the most widely used organism for ethanol production. The underlying goal for both strategies for consuming sugar mixtures has been to develop a single organism that can do it all
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