Effect of carbohydrate binding modules alterations on catalytic activity of glycoside hydrolase family 6 exoglucanase from Chaetomium thermophilum to cellulose.

Exoglucanase (CBH) is the rate limiting enzyme in the process of cellulose degradation. The carbohydrate binding module (CBM) can improve the accessibility of cellulase to substrate, thereby promoting the enzymatic hydrolysis of cellulase. In this study, the influence of CBM on the properties of GH6 exoglucanase from Chaetomium thermophilum (CtCBH) is systematically explored from three perspectives: the fusion of exogenous CBM, the exogenous CBM replacement of its own CBM, and the deletion of its own CBM. The parental and reconstructed CtCBH presented the same optimum pH (6.0) and temperature (60 °C) for maximum activity. Fusion of exogenous CBM increased the binding capacity of CtCBH to Avicel by 8% and 9%, respectively, but it had no significant effect on its catalytic activity. The exogenous CBM replacement of its own CBM resulted in a 12% reduction in the binding ability of CtCBH to Avicel, and a 26% reduction in the catalytic activity of Avicel. The deletion of its own CBM significantly reduced the binding ability of CtCBH to Avicel by approximately 53%, but its catalytic activity was not obviously reduced. These observations suggest that binding ability of CBM is not necessary for the catalysis of CtCBH.

Effect of Rhodococcus sp. pretreatment on cellulose hydrolysis of corn stalk.

Pretreatment can improve the hydrolysis efficiency of cellulose, in which biological pretreatment plays an important role. In the present study, we uncovered that Rhodococcus has the ability of lignin degradation, which can decompose lignin and serve as a carbon source to meet the needs of its own growth. We used Rhodococcus to pretreat the corn stalks and evaluate the effect on cellulose hydrolysis. The concentration of reducing sugar produced by the hydrolysis of corn stalk after pretreatment of Rhodococcus is 2.95 g/L. SEM imaging showed that Rhodococcus pretreatment resulted the surface of corn stalk to be no longer complete, some lamellar structures fall off, and leave obvious traces, and obvious delamination was found at the edge of the fault. AFM imaging showed that the pretreatment changed the lignin structure of the corn stalk material surface, resulting in a higher surface roughness of 9.37. These results indicated that Rhodococcus pretreatment can improve the saccharification efficiency of cellulose by removing lignin and increasing the surface roughness of the material.

Co-expression of cellulase and xylanase genes in Sacchromyces cerevisiae toward enhanced bioethanol production from corn stover.

Lignocellulose is considered as a good resource for producing renewable energy. Previous in vitro studies have shown the synergistic action between cellulase and xylanase during lignocellulose biohydrolysis. In order to achieve the same effect in S. cerevisiae to enhance the practical biotransformation, two recombinant Saccharomyces cerevisiae strains (INVSc1-CBH-CA and INVSc1-CBH-TS) with co-expressed cellulase and xylanase were constructed. The cellulase and xylanase activities in INVSc1-CBH-CA and INVSc1-CBH-TS were 716.43 U/mL and 205.13 U/mL, 931.27 U/mL and 413.70 U/mL, respectively. The recombinant S. cerevisiae can use the partly delignified corn stover (PDCS) more efficiently and more ethanol producted than S. cerevisiae only expressing cellulase. Fermentation with INVSc1-CBH-CA and INVSc1-CBH-TS using PDCS ethanol yields increased by 1.7 and 2.1 folds higher than INVSc1-CBH, 2.8 and 3.4 folds higher than the wild type S. cerevisiae. The strategy of co-expression cellulase and xylanase in saccharomyces cerevisiae is effective and can be a foundation to research the mechanism of synergy effect of cellulose and xylanase.