Effect of Dilute Alkali Pretreatment on Sugar Release from Transgenic Switchgrass

Abstract

The recalcitrance of lignocellulosic materials to biochemical conversion is a major hurdle for cost-effective production of cellulosic sugars that can be processed into fuels and valuable chemicals. In this study, Alamo switchgrass (Panicum virgatum L.) 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 5.8%. The ratios of acid soluble lignin (ASL) to acid insoluble lignin (AIL) in transgenic plants were 21.4-64.3% higher than those of conventional biomass. Both conventional and transgenic plants were pretreated with alkalis at mild temperatures: lime at 50°C and the combination of lime and NaOH at 21°C, followed by enzymatic hydrolysis with commercial cellulases and xylanases. At the recommended conditions (0.1 g/g raw biomass and 12 h) for lime pretreatment at 50°C, the glucan and xylan conversions of transgenic switchgrass were 12% and 10%, respectively, higher than those of conventional plant. These increases were reduced to 7% and 8% for glucan and xylan conversions, respectively, when the best conditions (0.025 g lime/g raw biomass, 0.1 g NaOH/g raw biomass, and 6 h) for combined alkali pretreatment at 21°C were employed. The results show that down-regulation of 4CL gene promoted enzymatic hydrolysis of plant cell walls following mild alkaline pretreatments.