Simultaneous saccharification and fermentation of pretreated hardwoods

Vinzant, Todd B.; Ehrman, Christine I.; Adney, William S.; Thomas, Steven R.; Himmel, Michael E.

doi:10.1007/bf02787987

Cited by 53 publications

(28 citation statements)

References 7 publications

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“…Although the common assumption is that high lignin content adversely affects enzymatic hydrolysis (7,25,26), we observed no influence of lignin content on sugar release for high S/G ratios (≥2.0) (Fig. 2 A-C).…”

Section: Discussionmentioning

confidence: 66%

Lignin content in natural Populus variants affects sugar release

Studer

DeMartini

Davis

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

546

510

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The primary obstacle to producing renewable fuels from lignocellulosic biomass is a plant's recalcitrance to releasing sugars bound in the cell wall. From a sample set of wood cores representing 1,100 individual undomesticated Populus trichocarpa trees, 47 extreme phenotypes were selected across measured lignin content and ratio of syringyl and guaiacyl units (S/G ratio). This subset was tested for total sugar release through enzymatic hydrolysis alone as well as through combined hot-water pretreatment and enzymatic hydrolysis using a high-throughput screening method. The total amount of glucan and xylan released varied widely among samples, with total sugar yields of up to 92% of the theoretical maximum. A strong negative correlation between sugar release and lignin content was only found for pretreated samples with an S/G ratio < 2.0. For higher S/G ratios, sugar release was generally higher, and the negative influence of lignin was less pronounced. When examined separately, only glucose release was correlated with lignin content and S/G ratio in this manner, whereas xylose release depended on the S/G ratio alone. For enzymatic hydrolysis without pretreatment, sugar release increased significantly with decreasing lignin content below 20%, irrespective of the S/G ratio. Furthermore, certain samples featuring average lignin content and S/G ratios exhibited exceptional sugar release. These facts suggest that factors beyond lignin and S/G ratio influence recalcitrance to sugar release and point to a critical need for deeper understanding of cell-wall structure before plants can be rationally engineered for reduced recalcitrance and efficient biofuels production. L ignocellulosic biomass is the only sustainable resource in terms of cost, availability, and scale that can be converted into liquid fuels to reduce the prevailing role of petroleum in providing energy for the world's transportation needs (1, 2) and to decrease the emissions of fossil CO 2 that damage the world's climate (3). The primary obstacle to producing liquid transportation fuels by bioconversion methods is the release of sugars in high quantities at low costs from recalcitrant lignocellulosic biomass feedstocks (4, 5). Genetic modification of plants to make them less recalcitrant is a promising path to address this challenge on the feedstock side, but the effort would be greatly aided by improving understanding of the fundamental relationship between cell-wall composition and sugar release through pretreatment and enzymatic hydrolysis.In this paper, we focus on the influence of lignin content and the ratio of its syringyl and guaiacyl units (S/G ratio) on recalcitrance to sugar release, because these two traits were previously identified as dominant factors (6). Although it is generally perceived that low lignin contents increase the ability of cellulolytic enzymes to hydrolyze plant fibers (7-11), only a limited number of studies investigated the effect of lignin S/G ratio on sugar release through combined pretreatment and enzymatic hydrolysis. A...

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Section: Discussionmentioning

confidence: 66%

Lignin content in natural Populus variants affects sugar release

Studer

DeMartini

Davis

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

546

510

View full text Add to dashboard Cite

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“…One of the major priorities of the national bioenergy research initiatives is to improve the conversion of biomass into various chemicals and fuels, which in turn will be essential for increasing net energy gain, decreasing carbon balance, reducing the production cost, enhancing water and soil conservations, and promoting the profitability and viability of bioethanol as a choice for transportation fuel [4][5][6]. Various strategies have been developed to improve the biomass conversion efficiency; however, significant challenges still exist for reducing the enzyme cost, developing simultaneous saccharification and fermentation, optimizing biorefinery processes, potential removing or replacing of the pretreatment step, and discovering novel biocatalysts with extreme condition tolerances [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]. The study of natural biocatalyst systems will help to address these challenges because many natural biocatalyst systems have evolved to convert lignocellulosic biomass with high efficiency and in a simultaneous pretreatment, saccharification and fermentation pattern [24][25][26][27].…”

Section: Introductionmentioning

confidence: 99%

Comparison of Insect Gut Cellulase and Xylanase Activity Across Different Insect Species with Distinct Food Sources

2010

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Insect guts represent unique natural biocatalyst systems for biocatalyst discovery and biomass deconstruction mechanism studies. In order to guide the further research for enzyme discovery and biodiversity analysis, we carried out comprehensive xylanase and cellulase activity assays for the gut contents of three insect species representing different orders and food sources. The three insect species are grasshopper (Acrididae sp.), woodborer (Cerambycidae spp.), and silkworm (Bombyx mori) to represent the wood-consuming, grass-consuming, and leaf-consuming insects from Orthoptera, Coleoptera, and Lepidoptera orders, respectively. Generally speaking, the enzyme activity assays have shown that the cellulase and xylanase activities for grasshopper and woodborer guts are significantly higher than those of silkworm under various conditions. In addition, both pH and temperature have a significant impact on the enzyme activities in the gut contents. For the grasshopper gut, the means of xylanase and cellulase activities at pH 7 were 3,397 and 404 μM mg −1 min −1 , which are significantly higher than the activities at pH 4 and 10 (P<0.05). However, woodborer guts have shown the highest cellulase activity at pH 10. The results suggested that systems similar to woodborer guts could be good resources for discovering alkaline-tolerant enzymes. Moreover, the enzyme activities in response to different substrate concentrations were also analyzed, which indicated that grasshopper gut had particularly high cellulase activity. The enzyme activities in response to the reaction time were also examined, and we found that the enzyme activities (micromolar per milligram per minute) of different insect gut juices in response to the increase of incubation time fit well to the power function equation (E c = K ⋅ t b ) with high coefficients (r 2 >0.99). The newly developed model serves well to compare the characteristics of the enzyme mixtures among different insect species, which can be applied to other studies of natural biocatalyst systems for the future. Overall, the data indicated that grasshopper and woodborer guts are valuable resources for discovering the novel biocatalysts for various biorefinery applications.

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“…Lignin present in the plant cell walls provides the plant with support. It is reported to be the most resistant to pretreatment processes (Vinzant et al 1997;Vailhé et al 1998;Chen and Dixon 2007). Lignin also inhibits enzymatic saccharification (Chen and Dixon 2007;Jackson et al 2008) and microbial growth during the fuel production process (Mills et al 2009).…”

Section: Mechanical Strength Testing Of Plant Stemsmentioning

confidence: 99%