Engineering Restricted Lignin and Enhanced Sugar Deposition in Secondary Cell Walls Enhances Monomeric Sugar Release
Lignocellulosic biomass has the potential to be a major source of renewable sugar for biofuel production. However, the lignin component, a complex and interlinked phenolic polymer, associates with secondary cell wall polysaccharides, rendering them less accessible to enzymatic hydrolysis to convert them to sugars. Therefore, before enzymatic hydrolysis, biomass must first be pretreated to make it more susceptible to saccharification and release high yields of fermentable sugars. To reduce the impact of lignin on limiting saccharification, researchers at the Department of Energy’s Joint BioEnergy Institute (JBEI) engineered Arabidopsis lines where lignin biosynthesis was repressed in fiber tissues but retained in the plant’s vessels, and polysaccharide deposition was enhanced in fiber cells. Growth of these engineered plants showed little to no apparent negative impact on growth phenotype. Analyses of these engineered Arabidopsis plants were conducted to determine if the engineered plants would yield more sugars than wild type. Both wild type and engineered plant biomasses were treated with an ionic liquid at either 70°C for 5 hours or 140°C for 3 hours. After pretreatment at 140°C and subsequent saccharification, the relative peak sugar recovery from biomass of engineered plants and wild type was not statistically different. However, reducing the pretreatment temperature to 70°C resulted in a higher peak sugar recovery for the engineered lines, but a significant reduction in the peak sugar recovery obtained from the wild type. These results demonstrate that employing cell wall engineering to decrease the recalcitrance of lignocellulosic biomass has the potential to drastically reduce the energy required for effective pretreatment.
Scullin, C., A. G. Cruz, Y.-D. Chuang, B. A. Simmons, D. Loque, and S. Singh. 2015. “Restricting Lignin and Enhancing Sugar Deposition in Secondary Cell Walls Enhances Monomeric Sugar Release After Low Temperature Ionic Liquid Pretreatment,” Biotechnology for Biofuels 8, 95. DOI: 10.1186/s13068-015-0275-2.