Enhanced cellulase recovery without β‐glucosidase supplementation for cellulosic ethanol production using an engineered strain and surfactant

Abstract

Recycling cellulases by substrate adsorption is a promising strategy for reducing the enzyme cost of cellulosic ethanol production. However, β-glucosidase has no carbohydrate-binding module (CBM). Thus, additional enzymes are required in each cycle to achieve a high ethanol yield. In this study, we report a new method of recycling cellulases without β-glucosidase supplementation using lignocellulosic substrate, an engineered strain expressing β-glucosidase and Tween 80. The cellulases and Tween 80 were added to an aqueous suspension of diluted sulfuric acid/ammonia-treated corncobs in a simultaneous saccharification and fermentation (SSF) process for ethanol production. Subsequently, the addition of fresh pretreated corncobs to the fermentation liquor and remaining solid residue provided substrates with absorbed cellulases for the next SSF cycle. This method provided excellent ethanol production in three successive SSF cycles without requiring the addition of new cellulases. For a 10% (w/v) solid loading, a cellulase dosage of 30 filter paper units (FPU)/g cellulose, 0.5% Tween 80, and 2 g/L of the engineered strain, approximately 90% of the initial ethanol concentration from the first SSF process was obtained in the next two SSF processes, with a total ethanol production of 306.27 g/kg corncobs and an enzyme productivity of 0.044 g/FPU. Tween 80 played an important role in enhancing cellulase recovery. This new enzyme recycling method is more efficient and practical than other reported methods. Biotechnol. Bioeng. 2017;114: 543-551. © 2016 Wiley Periodicals, Inc.

Real-Time Adsorption of Exo- and Endoglucanases on Cellulose: Effect of pH, Temperature, and Inhibitors

“…An important prerequisite for enzymatic hydrolysis is the effective adsorption of cellulases on the surface of lignocellulose, − which can be either reversible or irreversible. − After hydrolysis, some cellulases are released into the supernatant (liquid phase), while others stay attached to the residual substrate (solid phase). Although solution-phase cellulases can be readsorbed on fresh substrates for recycling or be collected by ultrafiltration, these methods cannot be used to directly recover substrate-bound enzymes. Therefore, the dynamics of cellulase adsorption on cellulose substrates under various conditions needs to be elucidated to be able to modulate lignocellulose hydrolysis and cellulase recovery. , …”

Recycling Strategy and Repression Elimination for Lignocellulosic-Based Farnesene Production with an Engineered Escherichia coli

“…While β-glucosidase is negligibly recovered during the cellulase recycling process, we propose the combination of recycling cellulase with an engineered yeast strain expressing heterologous β-glucosidase to reduce the β-glucosidase supplementation and the cost of enzymatic hydrolysis for ethanol production . Furthermore, to avoid additional β-glucosidase supplementation, we have also reported a novel method of recycling cellulases with the engineered yeast strain and Tween 80, presenting excellent ethanol production over three cycles . These results demonstrated that we have developed a simple, practical, and low-cost enzyme recycling strategy to reduce the cost of enzymatic utilization for the production of cellulosic ethanol.…”

“…25 Furthermore, to avoid additional β-glucosidase supplementation, we have also reported a novel method of recycling cellulases with the engineered yeast strain and Tween 80, presenting excellent ethanol production over three cycles. 26 These results demonstrated that we have developed a simple, practical, and low-cost enzyme recycling strategy to reduce the cost of enzymatic utilization for the production of cellulosic ethanol. In this study, a recycling corncob pretreatment and cellulose hydrolysis were investigated for high-efficiency utilization of corncobs to produce β-farnesene and reduce the cost of the lignocellulose pretreatment.…”

Effect of a Nonionic Surfactant on Enzymatic Hydrolysis of Lignocellulose Based on Lignocellulosic Features and Enzyme Adsorption

“…Initially, it was pointed out that the NIS aided cellulase to desorb from cellulose to make more free cellulase to participate in cellulosic hydrolysis. − Disrupting the substrate structure as well as stabilizing and stimulating enzyme activity were further thought as the positive influences of NIS on enzymatic hydrolysis of cellulose. , Nevertheless, Eriksson et al found that NIS hardly played any role as a substrate disrupter, an enzyme stabilizer, and an effector and explained that NIS improved EHLC by reducing the unproductive adsorption of the enzyme onto lignin . This has become the mainstream viewpoint, − but there have been still different theories on NIS improving EHLC. Rocha-Martín et al observed that PEG4000 could promote the enzymatic hydrolysis efficiency of microcrystalline cellulose more significantly than that of steam explosion-treated crop straw and pointed out that the improvement effect of NIS on glucose release during enzymatic hydrolysis of pretreated lignocellulose had hardly any relation with lignin .…”