Improved sugar yields from biomass sorghum feedstocks: comparing low-lignin mutants and pretreatment chemistries

Abstract

BackgroundFor biofuel production processes to be economically efficient, it is essential to maximize the production of monomeric carbohydrates from the structural carbohydrates of feedstocks. One strategy for maximizing carbohydrate production is to identify less recalcitrant feedstock cultivars by performing some type of experimental screening on a large and diverse set of candidate materials, or by identifying genetic modifications (random or directed mutations or transgenic plants) that provide decreased recalcitrance. Economic efficiency can also be increased using additional pretreatment processes such as deacetylation, which uses dilute NaOH to remove the acetyl groups of hemicellulose prior to dilute acid pretreatment. In this work, we used a laboratory-scale screening tool that mimics relevant thermochemical pretreatment conditions to compare the total sugar yield of three near-isogenic brown midrib (bmr) mutant lines and the wild-type (WT) sorghum cultivar. We then compared results obtained from the laboratory-scale screening pretreatment assay to a large-scale pretreatment system.ResultsAfter pretreatment and enzymatic hydrolysis, the bmr mutants had higher total sugar yields than the WT sorghum cultivar. Increased pretreatment temperatures increased reactivity for all sorghum samples reducing the differences observed at lower reaction temperatures. Deacetylation prior to dilute acid pretreatment increased the total sugar yield for all four sorghum samples, and reduced the differences in total sugar yields among them, but solubilized a sizable fraction of the non-structural carbohydrates. The general trends of increased total sugar yield in the bmr mutant compared to the WT seen at the laboratory scale were observed at the large-scale system. However, in the larger reactor system, the measured total sugar yields were lower and the difference in total sugar yield between the WT and bmr sorghum was larger.ConclusionsSorghum bmr mutants, which have a reduced lignin content showed higher total sugar yields than the WT cultivar after dilute acid pretreatment and enzymatic hydrolysis. Deacetylation prior to dilute acid pretreatment increased the total sugar yield for all four sorghum samples. However, since deacetylation also solubilizes a large fraction of the non-structural carbohydrates, the ability to derive value from these solubilized sugars will depend greatly on the proposed conversion process.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-016-0667-y) contains supplementary material, which is available to authorized users.

Composition and growth of sorghum biomass genotypes for ethanol production

“…In a breeding program, the existence of genetic variation between individuals is strictly necessary, since it allows the identification of the most suitable genotypes according to the performance related to the desirable characteristics. This fact is verified for the hybrids of sorghum biomass used in this study, which presented significance for some of their evaluated characters, mainly in the possibility of identifying less recalcitrant materials, maximizing the production of monomeric carbohydrates from the structural carbohydrates, and, therefore, alternative for the production of economically efficient biofuels [62].…”

Common metabolic networks contribute to carbon sink strength of sorghum internodes: implications for bioenergy improvement

“…Additionally, stem biomass composition results from the sorghum mutants in monolignol biosynthetic could also be explained this way. Near isogenic lines (NIL) carrying the bmr6 mutation in grain sorghum background showed significantly increased total free soluble sugars, whereas the effect of bmr12 mutant varied depending on genetic backgrounds [125]. Decreased lignin contents are associated with slightly, though statistically not significant, increase in stem sugar concentration, [126].…”

Lignocellulose binding of a Cel5A-RtCBM11 chimera with enhanced β-glucanase activity monitored by electron paramagnetic resonance

“…The final fractionation step is the removal of lignin, which has a supramolecular polymeric structure derived from aromatic groups linked by β- O -4a alkyl-ari-ether bonds [ 57 , 58 ]. The role of lignin in the plant cell wall is both structural and to protect from microbial degradation [ 59 ], and it has been suggested that the removal of lignin is the key to the increased hydrolysis of lignocellulosic material [ 58 , 60 – 63 ]. The EPR spectrum of the BsCel5A-RtCBM11 Y151R1 in the presence of the delignificated cell wall fraction (Fig.…”