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

Scullin C, Cruz AG, Chuang YD, Simmons BA, Loque D, Singh S - Biotechnol Biofuels (2015)

Bottom Line: 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.The 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.

View Article: PubMed Central - PubMed

Affiliation: Deconstruction Division, Joint BioEnergy Institute, Lawrence Berkeley National Laboratory, Berkeley, CA USA ; Biological and Materials Science Center, Sandia National Laboratories, Livermore, CA USA.

ABSTRACT

Background: Lignocellulosic 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.

Results: Engineered 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.

Conclusions: The 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.

No MeSH data available.


Confocal fluorescence imaging of Arabidopsis during [C2C1im][OAc] pretreatment at 70 °C for 11 h. Heating occurred during ramp from room temperature to 70 °C during the first 30 min of imaging. Horizontal panels show comparison of WT versus the engineered line LLHPL2 while the vertical panels show selected images of the time course (a, b) 0, (c, d) 5 h, (e, f) 10 h, scale bar 50 μm
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Fig4: Confocal fluorescence imaging of Arabidopsis during [C2C1im][OAc] pretreatment at 70 °C for 11 h. Heating occurred during ramp from room temperature to 70 °C during the first 30 min of imaging. Horizontal panels show comparison of WT versus the engineered line LLHPL2 while the vertical panels show selected images of the time course (a, b) 0, (c, d) 5 h, (e, f) 10 h, scale bar 50 μm

Mentions: All of the Arabidopsis samples were observed to swell during IL pretreatment at 140 °C for 3 h (see Additional files 1, 2, 3, and 4: Movies 1–4). The observed rate of dissolution due to [C2C1im][OAc] pretreatment, however, was slower for the WT than the engineered lines (Fig. 3, Additional file 5: Figure S1). Due to the relatively minor differences observed in the rate and extent of dissolution at 140 °C, the temperature was reduced to 70 °C to determine if there were any significant differences observed in swelling and dissolution between the WT and LLHPL2. At this set of pretreatment conditions, there was an initial swelling step observed after 1 h of pretreatment, followed by the onset of extensive swelling after 3–4.5 h (Additional file 6: Figure S2, Additional files 7 and 8: Movie 5 and 6). Based on these results, a pretreatment incubation of 5 h at 70 °C was selected as the new pretreatment condition (Fig. 4).Fig. 3


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

Scullin C, Cruz AG, Chuang YD, Simmons BA, Loque D, Singh S - Biotechnol Biofuels (2015)

Confocal fluorescence imaging of Arabidopsis during [C2C1im][OAc] pretreatment at 70 °C for 11 h. Heating occurred during ramp from room temperature to 70 °C during the first 30 min of imaging. Horizontal panels show comparison of WT versus the engineered line LLHPL2 while the vertical panels show selected images of the time course (a, b) 0, (c, d) 5 h, (e, f) 10 h, scale bar 50 μm
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4496950&req=5

Fig4: Confocal fluorescence imaging of Arabidopsis during [C2C1im][OAc] pretreatment at 70 °C for 11 h. Heating occurred during ramp from room temperature to 70 °C during the first 30 min of imaging. Horizontal panels show comparison of WT versus the engineered line LLHPL2 while the vertical panels show selected images of the time course (a, b) 0, (c, d) 5 h, (e, f) 10 h, scale bar 50 μm
Mentions: All of the Arabidopsis samples were observed to swell during IL pretreatment at 140 °C for 3 h (see Additional files 1, 2, 3, and 4: Movies 1–4). The observed rate of dissolution due to [C2C1im][OAc] pretreatment, however, was slower for the WT than the engineered lines (Fig. 3, Additional file 5: Figure S1). Due to the relatively minor differences observed in the rate and extent of dissolution at 140 °C, the temperature was reduced to 70 °C to determine if there were any significant differences observed in swelling and dissolution between the WT and LLHPL2. At this set of pretreatment conditions, there was an initial swelling step observed after 1 h of pretreatment, followed by the onset of extensive swelling after 3–4.5 h (Additional file 6: Figure S2, Additional files 7 and 8: Movie 5 and 6). Based on these results, a pretreatment incubation of 5 h at 70 °C was selected as the new pretreatment condition (Fig. 4).Fig. 3

Bottom Line: 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.The 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.

View Article: PubMed Central - PubMed

Affiliation: Deconstruction Division, Joint BioEnergy Institute, Lawrence Berkeley National Laboratory, Berkeley, CA USA ; Biological and Materials Science Center, Sandia National Laboratories, Livermore, CA USA.

ABSTRACT

Background: Lignocellulosic 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.

Results: Engineered 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.

Conclusions: The 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.

No MeSH data available.