Deep Eutectic Solvent Pretreatment of Transgenic Biomass With Increased C6C1 Lignin Monomers

Abstract

The complex and heterogeneous polyphenolic structure of lignin confers recalcitrance to plant cell walls and challenges biomass processing for agroindustrial applications. Recently, significant efforts have been made to alter lignin composition to overcome its inherent intractability. In this work, to overcome technical difficulties related to biomass recalcitrance, we report an integrated strategy combining biomass genetic engineering with a pretreatment using a bio-derived deep eutectic solvent (DES). In particular, we employed biomass from an Arabidopsis line that expressed a bacterial hydroxycinnamoyl-CoA hydratase-lyase (HCHL) in lignifying tissues, which results in the accumulation of unusual C 6 C 1 lignin monomers and a slight decrease in lignin molecular weight. The transgenic biomass was pretreated with renewable DES that can be synthesized from lignin-derived phenols. Biomass from the HCHL plant line containing C 6 C 1 monomers showed increased pretreatment efficiency and released more fermentable sugars up to 34% compared to WT biomass. The enhanced biomass saccharification of the HCHL line is likely due to a reduction of lignin recalcitrance caused by the overproduction of C 6 C 1 aromatics that act as degree of polymerization (DP) reducers and higher chemical reactivity of lignin structures with such C 6 C 1 aromatics. Overall, our findings demonstrate that strategic plant genetic engineering, along with renewable DES pretreatment, could enable the development of sustainable biorefinery.

Strategies for the production of biochemicals in bioenergy crops

“…Assessment of both strategies in sugarcane showed that HCHL was more efficient than UbiC, resulting in the production of 7.3% and 1.5% dry weight (DW) of 4-HBA glucosides in leaves and stems, respectively [26]. Moreover, analysis of lignin purified from Arabidopsis plants transformed with a HCHL gene showed the presence of 4-HBA and syringaldehyde units, as well as a reduction in the lignin degree of polymerization, which results in increases of biomass saccharification efficiency [27,28]. Therefore, the HCHL engineering strategy has the potential to bring two valuable traits in bioenergy crops, namely 'enhanced biomass deconstructability' and 'valueadded coproduct' .…”

Impacts of Hydrogen Bond Donor Structures in Phenolic Aldehyde Deep Eutectic Solvents on Pretreatment Efficiency

“…27−29 These phenolic compoundbased DESs have been successfully applied to several biomass feedstocks. [19][20][21]30,31 In addition, the different molar ratios and combinations of lignin-derived DESs were compared to evaluate the pretreatment efficiency. Kim et al tested several phenolic compounds, including vanillin, catechol, 4-hydroxybenzyl alcohol, and p-coumaric acid synthesized with ChCl for DES formation and compared their biomass pretreatment performance.…”

One-pot conversion of engineered poplar into biochemicals and biofuels using biocompatible deep eutectic solvents

“…Such C 6 C 1 lignin monomers act as "DP-reducers" that lead to shorter lignin polymers with higher reactivity towards chemical processing, resulting in improved pretreatment efficiency. 7,8 Another lignin engineering strategy involves the incorporation of monolignol conjugates (i.e., acylated monolignols) into lignin polymers to introduce chemically labile ester bonds. For example, heterologous expression of a feruloyl-CoA:monolignol transferase gene in hybrid poplar led to the incorporation of backbone-integrated ester linkages (i.e., "zip lignin"), which resulted in significantly improved saccharification yields following pretreatment under mild conditions.…”

“…Such C 6 C 1 lignin monomers act as “DP-reducers” that lead to shorter lignin polymers with higher reactivity towards chemical processing, resulting in improved pretreatment efficiency. 7,8…”