Submitted to: Bioresource Technology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/18/2012
Publication Date: 4/1/2012
Publication URL: handle.nal.usda.gov/10113/55220
Citation: Wang, Z., Li, R., Xu, J., Marita, J.M., Hatfield, R.D., Qu, R., Cheng, J.J. 2012. Sodium hydroxide pretreatment of genetically modified switchgrass for improved enzymatic release of sugars. Bioresource Technology. 110:364-370. Interpretive Summary: Availability and efficient conversion of biomass to bioenergy continues to be a growing concern to meet projected goals of ethanol production from cellulosic materials. One of the challenges facing cellulosic-based bioenergy is developing processes that can effectively break up plant cell walls to allow access to the cellulose contained within them. Lignin is a major component of cell walls. It can be likened to glue that coats the other components and holds them all together, forming a semi-rigid structure that holds the plant upright. Once lignin is in the cell wall, it is difficult to remove or modify it to allow free access to the other cell wall components. One approach to overcome this problem with lignin is to change the way it is made during the development of plants. Down-regulating specific genes necessary for making lignin has been used to modify switchgrass. By making slight changes in the process of lignin synthesis, the switchgrass contained 8.5% less lignin. These modifications also changed the composition of the lignin such that treatment with sodium hydroxide and high temperature (121° C) resulted in increased conversion efficiency of cellulose by 18% over the control switchgrass. The modest changes in lignin do not appear to decrease biomass production while increasing the amount of ethanol produced per ton of switchgrass, providing an economic advantage to producers.
Technical Abstract: Overcoming biomass recalcitrance to biological conversion has been the focus of enormous research efforts in the cellulosic biofuel area in the past decades. In this study, Alamo switchgrass was genetically transformed to suppress the expression of 4-coumarate-CoA ligase (4CL). The transgenic plants were determined to have lignin content reductions of up to 8.5% and an increased ratio of acid-soluble lignin (ASL) to acid-insoluble lignin (AIL) of 21.4:64.3%. To examine the impact of lignin modification on sugar release, both conventional and transgenic lines were pretreated with 0.5, 1, and 2% (w/v) NaOH for 15, 30, and 60 min at 121°C, followed by enzymatic hydrolysis. Compared with conventional plants, the transgenic lines showed markedly higher sugar release from the biomass. At the optimal pretreatment conditions of 1% NaOH and 30 min, the glucan and xylan conversion efficiency in the best transgenic lines were improved by 16 and 18%, respectively. The results suggest that higher ASL/AIL ratios may compromise the negative influence of high lignin content on biomass saccharification.