Abstract
Cellulases and hemicellulases are the main industrial sources from different microorganisms used to depolymerise plant biomass to simple sugars that are converted to chemical intermediates and biofuels, such as ethanol. Cellulases are formed adaptively, and several positive (xyr1, Ace2, HAP2/3/5) and negative (Ace1, Cre1) components involved in this regulation are now known. In this review, we summarise current knowledge about how cellulase biosynthesis is regulated, and outline recent approaches and suitable strategies for facilitating the targeted improvement of cellulase production by genetic engineering. Trichoderma reesei is the preferred organism for producing industrial cellulases. However, a more efficient heterologous expression system for enzymes from different organism is needed to further improve its cellulase mixture. In addition those optimizations of the promoter and linker for hybrid genes can dramatically improve the efficiency of heterologous expression of cellulase genes.
Highlights
Lignocellulosic materials are widely considered important sources for the production of sugar streams that can be fermented to ethanol and other organic chemicals [1]
The production of the main cellulases in Trichoderma is regulated at the transcriptional level depending on the carbon source available [13], the genes being repressed tightly by glucose and induced up to several thousand folds by cellulose or the disaccharide sophorose [14]
A novel endogenous glucose antirepression promoter proA from aspartic protease protein encoding the gene, proA were obtained by genome walking technology in filamentous fungi Hypocrea orientalis EU7-22 which could highly express under both induction and glucose repression condition for cellulase production
Summary
Lignocellulosic materials are widely considered important sources for the production of sugar streams that can be fermented to ethanol and other organic chemicals [1]. The T. reesei cellulase system has a deficient b-glucosidase (BGL) activity, which leads to the incomplete hydrolysis of cellobiose, causing serious inhibition of the enzymes [5]. It is an important industrial enzyme and finds applications in several industrial processes [9]. Cellulase is a multi-enzyme complex of three different enzymes: exoglucanase-/Cellobiohydrolases (CBH), endoglucanase (EG) and beta-glucosidase (BGL) which acts synergistically for complete hydrolysis of cellulose. The production of the main cellulases in Trichoderma is regulated at the transcriptional level depending on the carbon source available [13], the genes being repressed tightly by glucose and induced up to several thousand folds by cellulose or the disaccharide sophorose [14]. Little information is available on the molecular mechanism involved in the strong activation of the Cellulase genes
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