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Abstract Cellular import of D-xylose, the second most abundant sugar in typical lignocellulosic biomass, has been evidenced to be an energy-depriving process in bacterial biocatalysts. The sugar facilitator of Zymomonas mobilis, Glf, is capable of importing xylose at high rates without extra energy input, but is inhibited by D-glucose (the primary biomass sugar), potentially limiting the utility of this transporter for fermentation of sugar mixtures derived from lignocellulose. In this work we developed an Escherichia coli platform strain deficient in glucose and xylose transport to facilitate directed evolution of Glf to overcome glucose inhibition. Using this platform, we isolated nine Glf variants created by both random and site-saturation mutagenesis with increased xylose utilization rates ranging from 4.8-fold to 13-fold relative to wild-type Glf when fermenting 100 g l–1 glucose–xylose mixtures. Diverse point mutations such as A165M and L445I were discovered leading to released glucose inhibition. Most of these mutations likely alter sugar coordinating pocket for the 6-hydroxymethyl group of D-glucose. These discovered glucose-resistant Glf variants can be potentially used as energy-conservative alternatives to the native sugar transport systems of bacterial biocatalysts for fermentation of lignocellulose-derived sugars.
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Synergistic co‐utilization of biomass‐derived sugars enhances aromatic amino acid production by engineered Escherichia coli
Abstract Efficient co‐utilization of mixed sugar feedstocks remains a biomanufacturing challenge, thus motivating ongoing efforts to engineer microbes for improved conversion of glucose−xylose mixtures. This study focuses on enhancing phenylalanine production by engineeringEscherichia colito efficiently co‐utilize glucose and xylose. Flux balance analysis identified E4P flux as a bottleneck which could be alleviated by increasing the xylose‐to‐glucose flux ratio. A mutant copy of the xylose‐specific activator (XylR) was then introduced into the phenylalanine‐overproducingE. coliNST74, which relieved carbon catabolite repression and enabled efficient glucose−xylose co‐utilization. Carbon contribution analysis through13C‐fingerprinting showed a higher preference for xylose in the engineered strain (NST74X), suggesting superior catabolism of xylose relative to glucose. As a result, NST74X produced 1.76 g/L phenylalanine from a model glucose−xylose mixture; a threefold increase over NST74. Then, using biomass‐derived sugars, NST74X produced 1.2 g/L phenylalanine, representing a 1.9‐fold increase over NST74. Notably, and consistent with the carbon contribution analysis, thexylR*mutation resulted in a fourfold greater maximum rate of xylose consumption without significantly impeding the maximum rate of total sugar consumption (0.87 vs. 0.70 g/L‐h). This study presents a novel strategy for enhancing phenylalanine production through the co‐utilization of glucose and xylose in aerobicE. colicultures, and highlights the potential synergistic benefits associated with using substrate mixtures over single substrates when targeting specific products.
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- Award ID(s):
- 2146114
- PAR ID:
- 10472860
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Biotechnology and Bioengineering
- ISSN:
- 0006-3592
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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