The realm of cellulases in biorefinery development

Abstract

Geopolitical concerns (unstable supply of gasoline, environmental pollution, and regular price hikes), economic, and employment concerns have been prompting researchers, entrepreneurs, and policy makers to focus on harnessing the potential of lignocellulosic feedstock for fuel ethanol production and its commercialization. The carbohydrate skeleton of plant cell walls needs to be depolymerised into simpler sugars for their application in fermentation reactions as a chief carbon source of suitable ethnologic strains for ethanol production. The role of cellulolytic enzymes in the degradation of structural carbohydrates of the plant cell wall into ready-to-fermentable sugar stream is inevitable. Cellulase synergistically acts upon plant cell wall polysaccharides to release glucose into the liquid media. Cellulase predominantly dominates all the plant cell wall degrading enzymes due to their vast and diverse range of applications. Apart from the major applications of cellulases such as in detergent formulations, textile desizing, and development of monogastric feed for ruminants, their role in biorefinery is truly remarkable. This is a major area where new research tools based upon fermentation based formulations, biochemistry, and system biology to expedite the structure-function relationships of cellulases including cellulosomes and new designer enzymatic cocktails are required. In the last two decades, a considerable amount of research work has been performed on cellulases and their application in biomass saccharification. However, there are still technical and economic impediments to the development of an inexpensive commercial cellulase production process. Advancements in biotechnology such as screening of microorganisms, manipulation of novel cellulase encoding traits, site-specific mutagenesis, and modifications to the fermentation process could enhance the production of cellulases. Commercially, cheaper sources of carbohydrates and modified fermentation conditions could lead to more cost-effective production of cellulases with the goal to reduce the cost of ethanol production from lignocellulosics. Implementation of integrated steps like cellulase production and cellulase mediated saccharification of biomass in conjunction with the fermentation of released sugars in ethanol in a single step so called consolidated bio-processing (CBP) is very important to reduce the cost of bioethanol. This paper aims to explore and review the important findings in cellulase biotechnology and the forward path for new cutting edge opportunities in the success of biorefineries.

Optimization of selective production media for enhanced production of xylanases in submerged fermentation by Thielaviopsis basicola MTCC 1467 using L16 orthogonal array

“…Rising interests in sustainable development and environmentally benign practices, microbial enzyme mediated transformation processes have shown advantages as compared to the conventional chemical conversion processes (Chandel et al 2011a). In the last two decades, xylanases (EC.3.2.1.8) have shown a great deal of attention due to their vast biotechnological applications in food, feed and paper industries (Chandel et al 2007).…”

Rational design and evolutional fine tuning of Saccharomyces cerevisiae for biomass breakdown

“…CBHs can also hydrolyze microcrystalline cellulose, conceivably by 'peeling' cellulose chains from the microcrystalline structure. b-Glucosidases (BGLs) cleave soluble cellodextrins and cellobiose into glucose [9]. However, saccharification remains a major barrier to development of the lignocellulosic biorefinery.…”

“…Cellulose is hydrolyzed to glucose by the synergistic action of multiple enzymes [9,10]. Endoglucanases (EGs) randomly hydrolyze the b-glycoside linkages of internal amorphous regions in cellulose to produce oligosaccharides [10].…”

“…However, saccharification remains a major barrier to development of the lignocellulosic biorefinery. Some cellulases are inhibited by their final product, glucose [9]. Adsorption of cellulases onto the cellulose surface is partially irreversible [10,12].…”

High-throughput cloning, expression and purification of glycoside hydrolases using Ligation-Independent Cloning (LIC)

“…Enzymatic saccharification has gained prominence as the most promising approach for cellulose hydrolysis, which is considered a limiting step on lignocellulose utilization process [7][8][9]. Generally, multiple enzyme activities, including endoglucanase (EC 3.2.1.4), exoglucanase (EC 3.2.1.91) and b-glucosidase (EC 3.2.1.21) are required to release glucose molecules from cellulose [7,10], while xylose, mannose, galactose, rhamnose, and arabinose sugars are depolymerized from hemicellulose by hemicellulases [11]. As the cost of enzymes remains a key economic impediment to commercialization of biofuels, scientific efforts towards elucidation of their catalytic mechanisms, improvement of catalytic activity by enzymatic engineering, directed evolution and site-directed mutagenesis, as well as discovery of new enzymes are fundamental for enabling the cost decrease of enzymatic hydrolysis of biomass.…”