Abstract
This study examined the chemical structural characteristics of cellulolytic enzyme lignin isolated from switchgrass focusing on comparisons between wild-type control and caffeic acid 3-O-methyltransferase (COMT) down-regulated transgenic line. Nuclear magnetic resonance (NMR) techniques including 13C, 31P, and two-dimensional 13C-1H heteronuclear single quantum coherence (HSQC) as well as gel permeation chromatography (GPC) were employed. Compared to the wild-type, the COMT down-regulated transgenic switchgrass lignin demonstrated a decrease in syringyl (S): guaiacyl (G) ratio and p-coumarate:ferulate ratio, an increase in relative abundance of phenylcoumaran unit, and a comparable content of total free phenolic OH groups along with formation of benzodioxane unit. In addition, COMT down-regulation had no significant effects on the lignin molecular weights during its biosynthesis process.
Highlights
There is a growing focus on innovative technologies that shift bioethanol production to second generation cellulosic biofuels due to the competition between food resources and first generation biofuels derived from agricultural resources such as corn starch (Wyman, 1999; Wang et al, 2007; Rubin, 2008)
The caffeic acid 3-O-methyltransferase (COMT) down-regulation resulted in a reduction of ca. 14% in Klason lignin content in the transgenic lines when compared to the wild-type control
The COMT down-regulated transgenic switchgrass demonstrated a decrease in lignin content and structural alterations compared to the wild-type
Summary
There is a growing focus on innovative technologies that shift bioethanol production to second generation cellulosic biofuels due to the competition between food resources and first generation biofuels derived from agricultural resources such as corn starch (Wyman, 1999; Wang et al, 2007; Rubin, 2008) Lignocellulosic resources, such as energy crops and agricultural and forest residues, are readily becoming available for bioethanol production, their processing requires a costly pretreatment step to overcome their natural recalcitrance toward biological deconstruction to simple sugars (Sun and Cheng, 2002; Himmel et al, 2007; Pu et al, 2008; Somerville et al, 2010). In the past two decades, extensive research efforts have been directed at improving a diverse set of pretreatment technologies including: dilute acid, lime, hot water, steam explosion, ammonia, and organosolv pretreatments While these pretreatments have achieved various level of success in overcoming the recalcitrance of lignocellulosic biomass, the pretreatment step still remains one of the most expensive steps in the current biomass to bioethanol production platform. Addressing biomass recalcitrance through alternative approaches is a crucial issue to the widespread, low-cost generation of cellulosic biofuels
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