Phenotypic characterization of an engineered strain of Caldicellulosiruptor bescii with enhanced tolerance to furan aldehydes

Furan aldehydes such as furfural and 5-hydroxymethyl furfural (5-HMF) are generated from xylose and glucose, respectively, during dilute acid pretreatment of lignocellulosic biomass. These compounds inhibit subsequent microbial cell growth and fermentation of carbohydrates. A main thrust within the BioEnergy Science Center is to improve the performance of cellulolytic and thermophilic bacteria that are able to simultaneously deconstruct and ferment plant biomass into liquid transportation fuels. By using a rational engineering approach, we generated a strain of Caldicellulosiruptor bescii that is able to reduce furfural and 5-HMF to their respective alcohols, which are less toxic to the microorganism. Here, we present phenotypic data regarding the engineered strain (JWCB044) in comparison to the wild-type, as well as a lactate dehydrogenase (ldhA) mutant. The engineered strain exhibited improved cell yield in the presence of 5-15 mM furfural and 5-HMF. When grown in the presence of 15 mM furfural or 5-HMF, strain JWCB044 reduced these compounds to below the detection limit although at a slow rate relative to growth suggesting further improvements may be possible. A continuation of this research aims to create robust C. bescii strains that can tolerate lignocellulosic hydrolysates and serve as parent organisms for further improvements in biofuel production.