Pretreatments such as dilute
acid at elevated temperature are effective for the hydrolysis of
pentose polymers in
hemicellulose and also increase the access of
enzymes to
cellulose fibers. However, the fermentation of resulting syrups is hindered by minor reaction products such as
furfural from
pentose dehydration. To mitigate this problem, four genetic traits have been identified that increase
furfural tolerance in
ethanol-producing Escherichia coli LY180 (strain W derivative): increased expression of fucO, ucpA, or pntAB and deletion of yqhD. Plasmids and integrated strains were used to characterize epistatic interactions among traits and to identify the most effective combinations.
Furfural resistance traits were subsequently integrated into the chromosome of LY180 to construct strain XW129 (LY180 ΔyqhD ackA::PyadC'fucO-ucpA) for
ethanol. This same combination of traits was also constructed in
succinate biocatalysts (Escherichia coli strain C derivatives) and found to increase
furfural tolerance. Strains engineered for resistance to
furfural were also more resistant to the mixture of inhibitors in
hemicellulose hydrolysates, confirming the importance of
furfural as an inhibitory component. With resistant
biocatalysts, product yields (
ethanol and
succinate) from
hemicellulose syrups were equal to control fermentations in laboratory media without inhibitors. The combination of genetic traits identified for the production of
ethanol (strain W derivative) and
succinate (strain C derivative) may prove useful for other renewable chemicals from lignocellulosic
sugars.