Significance of Lignin S/G Ratio in Biomass Recalcitrance of Populus trichocarpa Variants for Bioethanol Production

Abstract

Lignin S/G ratio has been investigated as an important factor in biomass recalcitrance to bioethanol production. Because of the complexity and variety of biomass, recalcitrance was also reportedly influenced by several other factors, such as total lignin content, degree of cellulose polymerization, etc. In addition, the effect of S/G ratio on biomass conversion is not uniform across plant species. Herein, 11 Populus trichocarpa natural variants grown under the same conditions with similar total lignin content were selected to minimize the effects of other factors. The lignin S/G ratio of the selected P. trichocarpa natural variants showed negative correlations with p-hydroxybenzoate (PB) and β–5 linkage contents, while it had positive ones with β-O-4 linkage, lignin molecular weight, and ethanol production. This study showed the importance of lignin S/G ratio as an independent recalcitrance factor that may aid future energy crop engineering and biomass conversion strategies.

Use of the lignocellulose-degrading bacterium Caldicellulosiruptor bescii to assess recalcitrance and conversion of wild-type and transgenic poplar

“…The importance of the S/G ratio has been reported in prior work with various Populus species and ratios of such previous work are included in Table 1. While other work has highlighted the significance of the S/G ratio of lignin [5,23,32], no such a correlation of S/G to recalcitrance was noted with the microbial-based assay utilized in this study.…”

“…While the overall lignin content negatively correlated to the yield of fermentation products, the type of lignin present can also affect the recalcitrance of the lignocellulosic feedstock. A higher ratio of syringyl to guaiacol subunits (S/G ratio) present in the lignin has previously been suggested to improve the saccharification yield of P. trichocarpa and subsequent ethanol yield from fermentation of the enzymatically saccharified biomass with yeast [32]. For the lines tested here with available data on S/G ratio, the higher ratios correlated weakly with increased fermentation performance (R 2 = 0.41) (Fig.…”

“…Examples include the overexpression of xylem development regulatory genes [8], down-regulation of pectin synthesis [1], and overexpression of cell wall degrading enzymes, such as xyloglucanases [17], glycosyl hydrolases [31] and xylanases [21]. Natural variants with desirable properties have also been considered [14,23,32]. However, these approaches have not yet achieved the reductions in feedstock recalcitrance obtained through the use of systems biology-based approaches for generating transgenic plants with strategic properties.…”

Lignocellulosic Biomass: Understanding Recalcitrance and Predicting Hydrolysis

“…However, the correlation between lignin S/G ratio and recalcitrance is still not obvious. For example, Herbaut et al and Yu et al showed a positive correlation between the S/G ratio and the hydrolysis yields for miscanthus and woody chips (Yu et al, 2014;Herbaut et al, 2018) because of the higher binding capacity of G (with branched structure) over S (with linear structure and low degree of polymerisation) to cellulase (Guo et al, 2014;Yoo et al, 2017b). By contrast, others found a negative correlation between S/G ratio and the enzymatic hydrolysis in woody chips (Papa et al, 2012), in pretreated miscanthus (Xu et al, 2012;, in pre-treated wheat straw (Jiang et al, 2016) and in genetically engineering poplar (Escamez et al, 2017).…”

Multiscale analysis of lignocellulose recalcitrance towards OrganoCat pretreatment and fractionation

“…The molecular composition and structure of lignin plays an important role for biomass recalcitrance and subsequently lignin valorization [26,43]. In particular, the role of S/G ratio for recalcitrance has been intensively studied [48,49].…”