Metabolic engineering of yeasts by heterologous enzyme production for degradation of cellulose and hemicellulose from biomass: a perspective

Abstract

This review focuses on current approaches to metabolic engineering of ethanologenic yeast species for the production of bioethanol from complex lignocellulose biomass sources. The experimental strategies for the degradation of the cellulose and xylose-components of lignocellulose are reviewed. Limitations to the current approaches are discussed and novel solutions proposed.

Advances in consolidated bioprocessing systems for bioethanol and butanol production from biomass: a comprehensive review

“…So, designing a single microbe or microbial consortium with desired efficiency for this purpose is necessary (Kricka et al, 2014). Recently, two major strategies (native and recombinant) have been proposed to generate ideal microorganisms for CBP.…”

“…Commonly, cellulose hydrolysis occurs through the cooperation of three groups of gluconases, including endoglucanases (EGs) with activity on the amorphous regions of cellulose for production of free chain ends, exoglucanases (cellodextrinases and cellobiohydrolases (CBHs)) with activity on crystalline cellulose to release cellobiose from free chain ends, and β-glucosidases (BGLs) which hydrolyze cellobiose and small cello-oligosaccharides to glucose. It is generally accepted that these enzymes act sequentially and synergistically (Lynd et al, 2002;Zhang et al, 2004;den Haan et al, 2013;Kricka et al, 2014). In addition to cellulases, some other recently-described enzymes, such as the copper-requiring polysaccharide monooxygenases which have synergy with the exo-and endoglucanases, and elastin-like proteins which enhance access of the cellulases to the cellulose chains ends, are involved in lignocellulose hydrolysis (Leggio et al, 2012;Kubicek, 2013;Kricka et al, 2014;Nakatani et al, 2013).…”

“…The native strategy focuses on studying natural cellulolytic microbes with an aim to improve biofuel yield. Some native cellulolytic microorganisms, such as Clostridium sp., Bacillus subtilis and Trichoderma reesei are capable of producing only simple secondary metabolites such as ethanol or hydrogen (Kricka et al, 2014;Parisutham et al, 2014).Some methodologies, including isolation and characterization of new strains with CBP capacities, adaptive evolution using natural selection to specific environmental conditions (Gefen et al, 2012) or development of bioprocessing and fermentation systems to enhance CBP capabilities (Elkins et al, 2010;Liang et al, 2011;Wang et al, 2012a;Kricka et al, 2014) have also been used. In addition, recent studies have confirmed the feasibility to manipulate some cellulytic microorganisms e.g.…”

“…In addition to cellulases, some other recently-described enzymes, such as the copper-requiring polysaccharide monooxygenases which have synergy with the exo-and endoglucanases, and elastin-like proteins which enhance access of the cellulases to the cellulose chains ends, are involved in lignocellulose hydrolysis (Leggio et al, 2012;Kubicek, 2013;Kricka et al, 2014;Nakatani et al, 2013). Cellulase enzymes are naturally produced by a variety of fungi such as Trichoderma, Aspergillus, Talaromyces, and several anaerobic bacteria such as species of the Clostridium and Ruminococcus genera, which can be used as sources of cellulase genes for enhancing cellulase activity in yeasts (Martinez et al, 2008;Fontes and Gilbert, 2010;Kubicek, 2013;Kricka et al, 2014). To achieve an efficient and complete hydrolysis of lignocelluloses, at least one copy of each of the cellulase genes must be functionally expressed in the ethanologenic host organism (e.g.…”

“…These microorganisms should have specific traits, including expression and secretion of several glycoside hydrolase enzymes for rapid depolymerization of lignocellulose, simultaneous utilization and conversion of multiple sugars like cellobiose, glucose and xylose to biofuels, and tolerance both to toxic compounds derived from lignin and the final end product (Fig. 3) (Vinuselvi et al, 2011;Hasunuma and Kondo, 2012;Kricka et al, 2014;Kumagai et al, 2014;Parisutham et al, 2014). The enzymes needed to make the complete cellulolytic cocktail for the saccharification of lignocellulosic biomass are cellulases (cellobiohydrolase, endoglucanase, β-glucosidase and phospho-β-glucosidase), hemicellulases (endoxylanase, .…”