One of the approaches to utilize lignocellulosic biomass as feedstocks for biorefibery is through biological conversion. Currently, an efficient, rapid, and complete enzymatic hydrolysis of biomass using low enzyme loadings is still one of the major technical and economical bottlenecks in this process because of the lack of low cost pretreatment technology as well as high cost of enzymes. Since lignocellulosic biomass is composed of a matrix with multiple intertwined biopolymers (cellulose, hemicelluloses, lignin and extractives), it requires several different classes of enzymes in large quantities to efficiently release fermentable sugars. As a result, it is necessary to produce different classes of enzymes individually in a large scale and then make cocktails for biomass hydrolysis. Because of the high cost and limited capacity for producing these enzymes through fermentation, today, it is still a big challenge to develop an efficient enzyme production system for rapid and less expensive biomass depolymerization.
However, all these enzymes required for biomass enzymatic hydrolysis are produced naturally by a range of microbial species including bacteria and fungi. Many cell wall-degrading enzymes have been isolated and characterized and more are still not uncovered. Availability of genome sequences of Trichoderma reesei and other organisms have increased inventory of enzymes for biomass utilization.
Plants have already been used as a “factory” in industry to produce enzymes and other proteins, carbohydrates, lipids, industrial polymers and pharmaceuticals. Successful technology is available for plant genetic transformation, farming of transgenic crops and harvesting, transporting and processing the plant matter. Therefore, expression of all different classes of cell wall-degrading enzymes into plants provides great opportunity for developing biomass-specific enzyme cocktails, which will create a low sugar platform for biorefinery.
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