title: Lignin content in natural Populus variants affects sugar release.
abstract: 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.
authors: University of California, Bourns College of Engineering, Center for Environmental Research and Technology, Riverside, CA 92507, USA.
authors: Michael H
authors: MH
authors: Studer
authors: Jaclyn D
authors: JD
authors: DeMartini
authors: Mark F
authors: MF
authors: Davis
authors: Robert W
authors: RW
authors: Sykes
authors: Brian
authors: B
authors: Davison
authors: Martin
authors: M
authors: Keller
authors: Gerald A
authors: GA
authors: Tuskan
authors: Charles E
authors: CE
authors: Wyman
mesh_terms: D050260:Carbohydrate Metabolism; D005936:Glucans / Q000378:metabolism*; D008031:Lignin / Q000032:analysis*; D032107:Populus / Q000737:chemistry* / Q000378:metabolism*; D014990:Xylans / Q000378:metabolism*
chemical_list: D005936:Glucans; D014990:Xylans; D008031:Lignin