Recent advances in bioethanol production from lignocelluloses: a comprehensive review with a focus on enzyme engineering and designer biocatalysts

Abstract

Many countries have their biofuel policy programs in place as part of their overall strategy to achieve sustainable development. Among biofuels, bioethanol as a promising alternative to gasoline is of substantial interest. However, there is limited availability of a sufficient quantity of bioethanol to meet demands due to bottlenecks in the present technologies to convert non-edible feedstocks, including lignocelluloses. This review article presents and critically discusses the recent advances in the pretreatment of lignocellulosic biomass, with a focus on the use of green solvents, including ionic liquids and deep eutectic solvents, followed by enzymatic saccharification using auxiliary proteins for the efficient saccharification of pretreated biomass. Different techniques used in strain improvement strategies to develop hyper-producing deregulated lignocellulolytic strains are also compared and discussed. The advanced techniques employed for fermentation of mixed sugars contained in lignocellulosic hydrolysates for maximizing bioethanol production are summarized with an emphasis on pathway and transporters engineering for xylose assimilation. Further, the integration of different steps is suggested and discussed for efficient biomass utilization and improved ethanol yields and productivity.

Production of Endoglucanases by Streptomyces thermocoprophilus CP1 using Rice Straw as a Substrate

“…A suitable pretreatment method is a key in breaking down the recalcitrant lignin structure leading to the accessibility of cellulose towards hydrolytic enzymes for its conversion into monosaccharides. 15 There are various pretreatment processes applied for lignocellulosic biomass. The choice of pretreatment methods relies on economic factor, type of lignocellulosic feedstock, and environmental impacts.…”

“…To make concept of biorefineries economically feasible, genetic engineering techniques have been used recently to improve the enzymatic expression of microorganisms. 15 Unlike Escherichia coli, Streptromyces spp. have not been a popular microorganisms for metabolic engineering because they are not well-characterized.…”

“…The enzymes required for efficient deconstruction of polysaccharides into monomeric sugars include modular and nonmodular glycosyl hydrolases (GHs) comprising of cellulases and hemicellulases, carbohydrate esterases (CEs), and auxiliary activity (AA) proteins. 15 Rice straw is a major agricultural biomass waste produced in Southeast Asia and particularly in Thailand, and yet most of this biomass is left unutilized and is often burned in the field causing severe environmental problems at both local and global levels. It is estimated that over 20 million ton of rice straw are produced in Thailand every year.…”

Production of first- and second-generation ethanol for use in alcohol-based hand sanitizers and disinfectants in India

“…From the past few years, the utilization of low-cost agricultural feedstocks (mainly LCB) has captured scientific attention for the production of 2G ethanol. The integrated technologies that involve the costeffective production of bioethanol include SHF, SSF/SSCF, and CBP, which have already been discussed in Section 5.2 [101]. Such lignocellulosic feedstocks also provide tremendous opportunities in the healthcare sector for the production of disinfectants and hand sanitizers.…”

Life cycle assessment of bioethanol production from Pennisetum sp. using fed‐batch simultaneous saccharification and cofermentation at high solid loadings

“…6 However, the efficacy of the pretreatment is greatly dependent on the type of pretreatment and biomass used. Pretreatment of the biomass can be conducted by physical (milling and freezing), chemical (acid, alkali, organic acids, pH-controlled liquid hot water, and ionic liquids), physicochemical (steam explosion, ammonia fiber explosion, ammonia recycle percolation, carbon dioxide explosive, microwave/ultrasound-chemical, and liquid hot water) and biological (microorganisms) methods Kamusoko et al 7 and Cheah et al 8 Furthermore, recent pretreatment strategies such as dilute acid followed by microbial (Mucor indicus) digestion, ionic liquid pretreatments, and deep eutectic solvents (DESs) [9][10][11] have also been promising techniques for the pretreatment of lignocellulosic biomass. The latest pretreatment techniques and their mechanisms on lignocellulosic biomass have been extensively reviewed recently by Mirmohamadsadeghi et al 12 and Das et al 13 The pretreatment step transforms the macroscopic, microscopic, and submicroscopic structures of lignocellulosic biomass that leads to a decrease in the crystallinity of cellulose and lignin and further enhances the surface area of biomass for better accessibility of enzymes.…”