Cellulase recycling in biorefineries—is it possible?

Abstract

On a near future, bio-based economy will assume a key role in our lives. Lignocellulosic materials (e.g., agroforestry residues, industrial/solid wastes) represent a cheaper and environmentally friendly option to fossil fuels. Indeed, following suitable processing, they can be metabolized by different microorganisms to produce a wide range of compounds currently obtained by chemical synthesis. However, due to the recalcitrant nature of these materials, they cannot be directly used by microorganisms, the conversion of polysaccharides into simpler sugars being thus required. This conversion, which is usually undertaken enzymatically, represents a significant part on the final cost of the process. This fact has driven intense efforts on the reduction of the enzyme cost following different strategies. Here, we describe the fundamentals of the enzyme recycling technology, more specifically, cellulase recycling. We focus on the main strategies available for the recovery of both the liquid- and solid-bound enzyme fractions and discuss the relevant operational parameters (e.g., composition, temperature, additives, and pH). Although the efforts from the industry and enzyme suppliers are primarily oriented toward the development of enzyme cocktails able to quickly and effectively process biomass, it seems clear by now that enzyme recycling is technically possible.

Modification of paper properties using carbohydrate-binding module 3 from the Clostridium thermocellum CipA scaffolding protein produced in Pichia pastoris: elucidation of the glycosylation effect

“…Due to their independent fold and function, CBMs find application in different fields of biotechnology (Gomes et al 2015;Oliveira et al 2015). CBMs can be obtained from fungal and bacterial cellulases and hemicellulases through proteolysis (Lemos et al 2000;Pinto et al 2004a) or by recombinant DNA technology, mainly in fusion with a partner (reviewed in Oliveira et al 2015).…”

Consolidated bioprocessing of corn cob-derived hemicellulose: engineered industrial Saccharomyces cerevisiae as efficient whole cell biocatalysts

“…co-culture with cellulolytic strains for whole slurry CBP). Furthermore, this cell-surface display approach to CBP also facilitates the recycling of hydrolytic enzymes, an important technology for the development of economically viable processes [39]. In fact, cell recycling was attempted in CBP with ER-X-2P, and despite the gradual loss of yeast cell fermentative capacity, the hydrolytic activity of the cell-surface displayed enzymes was maintained after 2 cycles of recycling, releasing similar concentrations of xylose ( Fig.…”

An overview of the enzyme potential in bioenergy-producing biorefineries

“…Cellulases with modular structure from fungi and bacteria may present a cellulose binding domain (CBD), which is a 30 to 200 aminoacids sequence belonging to the carbohydrate binding modules (CBMs) class . CBDs are important for defining the affinity and specificity of cellulases towards lignocellulose fibers . Indeed, CBDs do not exert hydrolytic disruption of cellulose, but enable efficient enzyme adsorption to cellulose and its processive hydrolysis by impeding the cellulase to separate from the substrate after the cleavage of a glycosidic bond and sliding towards the next one.…”

“…Indeed, CBDs do not exert hydrolytic disruption of cellulose, but enable efficient enzyme adsorption to cellulose and its processive hydrolysis by impeding the cellulase to separate from the substrate after the cleavage of a glycosidic bond and sliding towards the next one. In contrast β‐glucosidases are not acknowledged to present CBD, a reason whence these have the least binding affinity to cellulose after endoglucanases and cellobiohydrolases . CBDs are not exclusive of cellulases, they have also been found in mannanases, xylanases, estereases and pectate‐lyases…”