Significantly enhanced bioconversion of high titer biomass-derived furfural to furfuryl alcohol by robust endogenous aldehyde reductase in a sustainable way

The highly efficient manufacturing of valuable biofurans from abundant, available and renewable bioresources has attracted much attention in a sustainable way. The major aim of this study is to first construct an effective and sustainable route for chemoenzymatically transforming lignocellulose to furfuryl alcohol (FOL) via sequential catalysis with a biocompatible biochar-based heterogeneous chemocatalyst and a robust reductase biocatalyst in a one-pot two-step manner. Escherichia coli cells co-expressing endogenous aldehyde reductase (ALR) from E. coli BL21(DE3) and formate dehydrogenase (FDH) from Candida boidinii were first constructed to efficiently transform a high titer of furfural (FAL) (>= 300 mM) into furfuryl alcohol after 3 h with in situ coenzyme recycling. Whole-cells of recombinant Escherichia coli FF182 harbored good bioreduction activity, with high tolerance toward a high titer of furfural (up to 350 mM), well-known potent inhibitors against microorganisms. Molecular docking (MD) simulation indicated that the furfural molecule showed -4.4 kcal mol(-1) binding energy at the binding site containing two hydrogen bonds with interacting amino acid residues Gly14 and Ala178, suggesting that ALR in FF182 cells had a high affinity for furfural and good bioreduction activity. Furfuryl alcohol could be acquired at >99% yield (analytical yield) from furfural (300 mM) by FF182 cell with HCOONa (as co-substrate) in an aqueous medium (30 degrees C and pH 7.0) within 3 h. Lignocellulose-valorized furfural (103.5 mM), which was obtained from the transformation of corncob by a biochar-based heterogeneous chemocatalyst with 0.1 wt% of HCOOH, was fully reduced into furfuryl alcohol, with a productivity of 0.36 gram furfuryl alcohol per gram xylan in corncob. The improved substrate tolerance of FF182 cells is gaining considerable interest in the synthesis of value-added furan-based alcohols, which have potential industrial applications.