Tissue specific analysis of bioconversion traits in the bioenergy grass Sorghum bicolor

Abstract

In order for lignocellulose conversion to bioenergy products to be optimal, biomass hydrolysis efficiency must be increased. In conjunction with optimized enzymes and pretreatment strategies, genetic improvement of feedstock conversion potential is a common sense approach to increase end product yield. In this study, feedstock composition and crystallinity index traits were investigated across twenty Sorghum bicolor varieties for tissue specific relationships with enzymatic hydrolysis (Trichoderma viride and Aspergillus niger cellulases). It was found that hydrolysis yield potential was higher in stem than in leaf tissue. Lignin content was shown to be negatively correlated with hydrolysis rates in leaf but not stem tissue. Crystallinity index was negatively correlated with stem tissue hydrolysis rate in two grow-out years. In addition, pretreatment efficacy varied among tissue types of multiple genotypes. Dose–response curves for T. viride cellulase and ammonium hydroxide pretreatment revealed genotype and tissue specific hydrolysis rates, which suggests that these factors be optimized prior to large-scale implementation of a specific feedstock–conversion process combination. Butanol production correlates with hydrolysis rate in stem but not leaf tissue. This study suggests that selection of specific sorghum genotypes with high stem to leaf ratios could improve hydrolysis efficiency and end product yield.