Restricting lignin and enhancing sugar deposition in secondary cell walls enhances monomeric sugar release after low temperature ionic liquid pretreatment

Abstract

BackgroundLignocellulosic biomass has the potential to be a major source of renewable sugar for biofuel production. Before enzymatic hydrolysis, biomass must first undergo a pretreatment step in order to be more susceptible to saccharification and generate high yields of fermentable sugars. Lignin, a complex, interlinked, phenolic polymer, associates with secondary cell wall polysaccharides, rendering them less accessible to enzymatic hydrolysis. Herein, we describe the analysis of engineered Arabidopsis lines where lignin biosynthesis was repressed in fiber tissues but retained in the vessels, and polysaccharide deposition was enhanced in fiber cells with little to no apparent negative impact on growth phenotype.ResultsEngineered Arabidopsis plants were treated with the ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate 1-ethyl-3-methylimidazolium acetate ([C2C1im][OAc]) at 10 % wt biomass loading at either 70 °C for 5 h or 140 °C for 3 h. After pretreatment at 140 °C and subsequent saccharification, the relative peak sugar recovery of ~26.7 g sugar per 100 g biomass was not statistically different for the wild type than the peak recovery of ~25.8 g sugar per 100 g biomass for the engineered plants (84 versus 86 % glucose from the starting biomass). Reducing the pretreatment temperature to 70 °C for 5 h resulted in a significant reduction in the peak sugar recovery obtained from the wild type to 16.2 g sugar per 100 g biomass, whereas the engineered lines with reduced lignin content exhibit a higher peak sugar recovery of 27.3 g sugar per 100 g biomass and 79 % glucose recoveries.ConclusionsThe engineered Arabidopsis lines generate high sugar yields after pretreatment at 70 °C for 5 h and subsequent saccharification, while the wild type exhibits a reduced sugar yield relative to those obtained after pretreatment at 140 °C. Our results demonstrate that employing cell wall engineering efforts to decrease the recalcitrance of lignocellulosic biomass has the potential to drastically reduce the energy required for effective pretreatment.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-015-0275-2) contains supplementary material, which is available to authorized users.

Cell Wall Composition and Underlying QTL in an F1 Pseudo-Testcross Population of Switchgrass

“…Lignification and cross-linkage of lignin with other cell wall components form a natural barrier against the penetration of disparaging enzymes through the cell wall [42]. This barrier negatively impacts sugar release from cellulose and hemicellulose [43]. We found that a 1 % (Fig.…”

Impact of lignin polymer backbone esters on ionic liquid pretreatment of poplar

“…Similarly, poplars downregulated in cinnamoyl - CoA reductase ( CCR ) had more facile saccharification but at a biomass yield penalty [ 8 ]. A selective reduction in lignin and increase in cellulose accumulation was shown to impact the secondary cell wall structure in Arabidopsis [ 9 ]. Recently, with the basic idea of introducing readily cleavable bonds into the lignin backbone to lower the energy requirement for biomass processing, poplar was engineered to produce monolignol ferulate conjugates to augment the monomer pool by introducing an exotic feruloyl - CoA monolignol transferase ( FMT ) genes [ 4 ].…”

Facile isothermal solid acid catalyzed ionic liquid pretreatments to enhance the combined sugars production from Arundo donax Linn.

“…2 ). Both R110-1.0 and R120-0.5 samples have significantly increased total sugars recovery (29.5 and 30.9 g total sugar per 100 g starting biomass) in the enzymatic hydrolysates as compared to the 8.3 and 8.4 g total sugars per 100 g starting biomass from the corresponding water pretreated samples (Table 3 , Additional file 1 ), which was higher than those of Arabidopsis pretreated with [C 2 mim][OAc] at 140 °C for 3 h [ 37 ].…”