Abstract
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.
Highlights
Value 42 glucose inhibition constant for cellulase (g/L) 13 g/L 3 g/L 100 h−1 2 g/L 1 g/L to cellulose properties like crystallinity, and enzyme interactions with cell wall matrix polymers including lignin and xylan which typically have negative effects on the digestion of biomass[10,11,12,13,14,15]
The alkaline peroxide (AP) treated corn stover is primarily comprised of glucan and xylan, with little lignin remaining, and the Clean Fractionation (CF) process treated corn stover contains primarily glucan, with a minimal amount of xylan or lignin content (Table S1)
Augmented CelA based mixes were much more efficient at converting biomass on a molar basis when compared to optimized fungal cellulase mixtures acting on all substrates tested
Summary
Value 42 g/L 13 g/L 3 g/L 100 h−1 2 g/L 1 g/L to cellulose properties like crystallinity, and enzyme interactions with cell wall matrix polymers including lignin and xylan which typically have negative effects on the digestion of biomass[10,11,12,13,14,15]. These additional substrate factors determine the recalcitrance of biomass and can dominate the interaction of cellulolytic enzyme systems with whole biomass. We aim to explain how these factors affect the deconstruction of biomass by CelA
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