The Multi Domain Caldicellulosiruptor bescii CelA Cellulase Excels at the Hydrolysis of Crystalline Cellulose.

The crystalline nature of cellulose microfibrils is one of the key factors influencing biomass recalcitrance which is a key technical and economic barrier to overcome to make cellulosic biofuels a commercial reality. To date, all known fungal enzymes tested have great difficulty degrading highly crystalline cellulosic substrates. We have demonstrated that the CelA cellulase from Caldicellulosiruptor bescii degrades highly crystalline cellulose as well as low crystallinity substrates making it the only known cellulase to function well on highly crystalline cellulose. Unlike the secretomes of cellulolytic fungi, which typically comprise multiple, single catalytic domain enzymes for biomass degradation, some bacterial systems employ an alternative strategy that utilizes multi-catalytic domain cellulases. Additionally, CelA is extremely thermostable and highly active at elevated temperatures, unlike commercial fungal cellulases. Furthermore we have determined that the factors negatively affecting digestion of lignocellulosic materials by C. bescii enzyme cocktails containing CelA appear to be significantly different from the performance barriers affecting fungal cellulases. Here, we explore the activity and degradation mechanism of CelA on a variety of pretreated substrates to better understand how the different bulk components of biomass, such as xylan and lignin, impact its performance.

Evaluation of different biomass materials as feedstock for fermentable sugar production.

Saline crops and autoclaved municipal organic solid wastes were evaluated for their potential to be used as feedstock for fermentable sugar production through dilute acid pretreatment and enzymatic hydrolysis. The saline crops included two woods, athel (Tamarix aphylla L) and eucalyptus (Eucalyptus camaldulensis), and two grasses, Jose tall wheatgrass (Agropyron elongatum), and creeping wild rye (Leymus triticoides). Each of the biomass materials was first treated with dilute sulfuric acid under selected conditions (acid concentration =1.4% (w/w), temperature =165 degrees C, and time =8 min) and then treated with the enzymes (cellulases and beta-glucosidase). The chemical composition (cellulose, hemicellulose, and lignin contents) of each biomass material and the yield of total and different types of sugars after the acid and enzyme treatment were determined. The results showed that among the saline crops evaluated, the two grasses (creeping wild rye and Jose tall wheatgrass) had the highest glucose yield (87% of total cellulose hydrolyzed) and fastest reaction rate during the enzyme treatment. The autoclaved municipal organic solid wastes showed reasonable glucose yield (64%). Of the two wood species evaluated, Athel has higher glucose yield (60% conversion of cellulose) than eucalyptus (38% conversion of cellulose).