Biomass Recalcitrance: Engineering Plants and Enzymes for Biofuels Production

Abstract

Lignocellulosic biomass has long been recognized as a potential sustainable source of mixed sugars for fermentation to biofuels and other biomaterials. Several technologies have been developed during the past 80 years that allow this conversion process to occur, and the clear objective now is to make this process cost-competitive in today's markets. Here, we consider the natural resistance of plant cell walls to microbial and enzymatic deconstruction, collectively known as "biomass recalcitrance." It is this property of plants that is largely responsible for the high cost of lignocellulose conversion. To achieve sustainable energy production, it will be necessary to overcome the chemical and structural properties that have evolved in biomass to prevent its disassembly.

Efficient Cleavage of Lignin–Carbohydrate Complexes and Ultrafast Extraction of Lignin Oligomers from Wood Biomass by Microwave‐Assisted Treatment with Deep Eutectic Solvent

“…Although numerous methods for refining lignocellulose have been developed in recent years, it still remains a serious challenge to break the recalcitrance of biomass through an energetically efficient and environmentally friendly process 8, 9. Biomass recalcitrance generally arises from lignin–carbohydrate complexes (LCCs), in which lignin is mainly covalently bonded to hemicellulose 10, 11.…”

Transgenic switchgrass (Panicum virgatum L.) targeted for reduced recalcitrance to bioconversion: a 2‐year comparative analysis of field‐grown lines modified for target gene or genetic element expression

“…However, it is economically challenging to convert lignocellulosic biomass to fuels. The inherent recalcitrance of biomass to sugar depolymerization is largely responsible for the high industrial cost of lignocellulose bioconversion (Himmel et al ., 2007). Recalcitrance can be defined as ‘the natural resistance of plant cell walls to microbial and enzymatic deconstruction’ (Himmel et al ., 2007) due to its complex carbohydrate‐ and lignin‐based structure.…”

Comparative study of corn stover pretreated by dilute acid and cellulose solvent‐based lignocellulose fractionation: Enzymatic hydrolysis, supramolecular structure, and substrate accessibility

“…Use of biofuels will offer several benefits, including reduced greenhouse gas emissions, decreased competition with tightening food supplies, enhanced rural economic development, and increased national energy security (Demain et al, 2005;Himmel et al, 2007;Lynd et al, 2002;Zhang et al, 2006b).…”

“…Lignoellulosic biomass, such as agricultural and forestry residues, municipal and industrial solid wastes, and herbaceous and woody bioenergy plants, is a natural complex composite primarily consisting of three biopolymers: cellulose, hemicelluloses, and lignin (Fengel and Wegener, 1984;Himmel et al, 2007;Lynd et al, 2002;Zhang, 2008). Efficient, cost-competitive production of fermentable sugars from recalcitrant biomass remains the largest obstacle to emerging cellulosic ethanol biorefineries (Lynd et al, 2008;Wyman, 2007;Zhang, 2008).…”

“…The root causes of biomass recalcitrance could be attributed to a number of factors, such as substrate accessibility to cellulase, cellulose degree of polymerization (DP), cellulose crystallinity, lignin content and structure, and hemicellulose content (Chandra et al, 2007;Himmel et al, 2007;Kim and Holtzapple, 2005;Zhang and Lynd, 2004;Zhang et al, 2006b). A functionally based mathematical model of fungal enzyme-based enzymatic cellulose hydrolysis has been developed, accounting for cellulose characteristics (DP and substrate accessibility) and different modes of action for endoglucanase and cellobiohydrolase enzyme system components (Zhang and Lynd, 2006).…”