Overcoming cellulose recalcitrance in woody biomass for the lignin-first biorefinery

Abstract

Background Low-temperature swelling of cotton linter cellulose and subsequent gelatinization in trifluoroacetic acid (TFA) greatly enhance rates of enzymatic digestion or maleic acid–AlCl 3 catalyzed conversion to hydroxymethylfurfural (HMF) and levulinic acid (LA). However, lignin inhibits low-temperature swelling of TFA-treated intact wood particles from hybrid poplar ( Populus tremula × P. alba ) and results in greatly reduced yields of glucose or catalytic conversion compared to lignin-free cellulose. Previous studies have established that wood particles from transgenic lines of hybrid poplar with high syringyl (S) lignin content give greater glucose yields following enzymatic digestion. Results Low-temperature (− 20 °C) treatment of S-lignin-rich poplar wood particles in TFA slightly increased yields of glucose from enzymatic digestions and HMF and LA from maleic acid–AlCl 3 catalysis. Subsequent gelatinization at 55 °C resulted in over 80% digestion of cellulose in only 3 to 6 h with high-S-lignin wood, compared to 20–60% digestion in the wild-type poplar hybrid and transgenic lines high in guaiacyl lignin or 5-hydroxy-G lignin. Disassembly of lignin in woody particles by Ni/C catalytic systems improved yields of glucose by enzymatic digestion or catalytic conversion to HMF and LA. Although lignin was completely removed by Ni/C-catalyzed delignification (CDL) treatment, recalcitrance to enzymatic digestion of cellulose from the high-S lines was reduced compared to other lignin variants. However, cellulose still exhibited considerable recalcitrance to complete enzymatic digestion or catalytic conversion after complete delignification. Low-temperature swelling of the CDL-treated wood particles in TFA resulted in nearly complete enzymatic hydrolysis, regardless of original lignin composition. Conclusions Genetic modification of lignin composition can enhance the portfolio of aromatic products obtained from lignocellulosic biomass while promoting disassembly into biofuel and bioproduct substrates. CDL enhances rates of enzymatic digestion and chemical conversion, but cellulose remains intrinsically recalcitrant. Cold TFA is sufficient to overcome this recalcitrance after CDL treatment. Our results inform a ‘no carbon left behind’ strategy to convert total woody biomass into lignin, cellulose, and hemicellulose value streams for the future biorefinery. Electronic supplementary material The online version of this article (10.1186/s13068-019-1503-y) contains supplementary material, which is available to authorized users.

Rhamnogalacturonan‐I is a determinant of cell–cell adhesion in poplar wood

“…Transgenic plant production and processing High-S and -G variants were produced in hybrid poplar clone INRA 717-1B4 (female, Populus tremula 9 P. alba) using transgenesis as described previously (Yang et al, 2019). For high-S lignin variants, cDNA of an A. thaliana F5H1 gene (FAH1, At4g36220) was over-expressed under control of a promoter from the A. thaliana C4H gene (AtC4H) (Bell-Lelong et al, 1997).…”

“…For high-S lignin variants, cDNA of an A. thaliana F5H1 gene (FAH1, At4g36220) was over-expressed under control of a promoter from the A. thaliana C4H gene (AtC4H) (Bell-Lelong et al, 1997). For high-G-lignin variants, RNAi constructs were designed from conserved consensus sequences of the poplar F5H2 (P. trichocarpa 'Nisqually' 1/383-2499) (Yang et al, 2019).…”

Potential applications of pecan residual biomasses: a review

“…However, there are other compounds of great interest especially using as renewable energy and for the production of bioproducts. Generally, lignocellulosic materials have a mass composition of 35 to 55% cellulose, 20 to 40% hemicelluloses and 10 to 25% lignin, and other elements such as extracts and minerals [10].…”

Succession of physiological stages hallmarks the transcriptomic response of the fungus Aspergillus niger to lignocellulose

“…In biotechnology, strategies to overcome substrate recalcitrance include engineering of enzyme cocktails and microbial strains for improved degradation as well as improving biomass digestibility via engineering of its composition or structure, or via chemical or physical pretreatment [6,[20][21][22]. Pretreatments, currently essential for effective lignocellulose processing, increase biomass digestibility via various mechanisms.…”