Engineering a Xylanlytic E. Coli for Bioenthanol and Bio-Refinery

E. coli has previously been engineered into an efficient biocatalyst for biofuel and other bioproducts from fermentable sugars such as glucose. However, E. coli is unable to utilize lignocelluloses directly, necessitating costly pretreatment and enzymatic hydrolysis. In an effort to consolidate lignocelluloses bioprocessing, we engineered an E. coli strain to use xylan directly. To this end, the necessary xylanase was overexpressed and secreted into growth medium with about 90% efficiency. In addition, we cloned and expressed a heterologous xylodextrin transport and metabolism operon from two different microbial sources. The operon codes a transporter for xylooligosaccharides and a xylosidase. The introduction of the operon allowed the uptake of xylooligosaccharides and its break down into xylose. When an E. coli ethanol producer was engineered to overexpress xylanase and the operon, ethanol was produced directly from birchwood xylan, demonstrating the validity of the strategy. Further improvement in hydrolysis yield and ethanol production is being made through co-expression of other accessory enzymes such as acetyl-xylan esterase and arabinofuranosidase.