13-03: Cellulose amorphogenesis: Can it enhance the effectiveness of cellulases?

Achieving efficient, rapid and complete cellulose saccharification using low protein loadings has proven to be one of the major technical and economical bottlenecks in the biomass-to-ethanol process. This is partially due to the high enzyme loadings that are typically required to overcome the limited accessibility to the cellulose and the relatively slow catalytic attack of cellulases. Although generally overlooked and not yet well understood,  several (ligno)cellulosic microorganisms have developed specific systems where the fibrillar structures of the cellulosic substrate are initially loosened, swollen, disrupted, delaminated or fragmented, consequently increasing the accessibly of the cellulose and exposing new glycosidic linkages. This process has been termed “amorphogenesis”. Amorphogenesis has been shown to enhance the accessibility of cellulosic substrates and, consequently, the effectiveness of cellulases. We have been assessing the various substrate- and enzyme-related factors that are thought to be primarily responsible for the slowdown in the rate and, in many cases, the incomplete hydrolysis of cellulosic materials. We have found that accessibility to cellulose is a key determinant in the effectiveness of hydrolysis of a range of pretreated lignocellulosic substrates when statistically optimized minimal enzyme loading were used.  It was also apparent that non-hydrolytic-mediated treatments swelled lignocellulosic substrates allowing carbohydrates to be more readily attacked by glycosidases. By increasing the accessibility of the cellulose within pretreated lignocellulosic substrates we were able to substantially increase the effectiveness of cellulases. The possible role of amorphogenesis, with the goal of reducing the overall enzyme loading required to carry out effective cellulose hydrolysis, will be discussed.