CELF significantly reduces milling requirements and improves soaking effectiveness for maximum sugar recovery of Alamo switchgrass over dilute sulfuric acid pretreatment

BACKGROUND

Pretreatment is effective in reducing the natural recalcitrance of plant biomass so polysaccharides in cell walls can be accessed for conversion to sugars. Furthermore, lignocellulosic biomass must typically be reduced in size to increase the pretreatment effectiveness and realize high sugar yields. However, biomass size reduction is a very energy-intensive operation and contributes significantly to the overall capital cost.

RESULTS

In this study, the effect of particle size reduction and biomass presoaking on the deconstruction of Alamo switchgrass was examined prior to pretreatment by dilute sulfuric acid (DSA) and Co-solvent Enhanced Lignocellulosic Fractionation (CELF) at pretreatment conditions optimized for maximum sugar release by each pretreatment coupled with subsequent enzymatic hydrolysis. Sugar yields by enzymatic hydrolysis were measured over a range of enzyme loadings. In general, DSA successfully solubilized hemicellulose, while CELF removed nearly 80% of Klason lignin from switchgrass in addition to the majority of hemicellulose. Presoaking and particle size reduction did not have a significant impact on biomass compositions after pretreatment for both DSA and CELF. However, presoaking for 4 h slightly increased sugar yields by enzymatic hydrolysis of DSA-pretreated switchgrass compared to unsoaked samples, whereas sugar yields from enzymatic hydrolysis of CELF solids continued to increase substantially for up to 18 h of presoaking time. Of particular importance, DSA required particle size reduction by knife milling to < 2 mm in order to achieve adequate sugar yields by subsequent enzymatic hydrolysis. CELF solids, on the other hand, realized nearly identical sugar yields from unmilled and milled switchgrass even at very low enzyme loadings.

CONCLUSIONS

CELF was capable of achieving nearly theoretical sugar yields from enzymatic hydrolysis of pretreated switchgrass solids without size reduction, unlike DSA. These results indicate that CELF may be able to eliminate particle size reduction prior to pretreatment and thereby reduce overall costs of biological processing of biomass to fuels. In addition, presoaking proved much more effective for CELF than for DSA, particularly at low enzyme loadings.

Genome-wide association studies and expression-based quantitative trait loci analyses reveal roles of HCT2 in caffeoylquinic acid biosynthesis and its regulation by defense-responsive transcription factors in Populus

3-O-caffeoylquinic acid, also known as chlorogenic acid (CGA), functions as an intermediate in lignin biosynthesis in the phenylpropanoid pathway. It is widely distributed among numerous plant species and acts as an antioxidant in both plants and animals. Using GC-MS, we discovered consistent and extreme variation in CGA content across a population of 739 4-yr-old Populus trichocarpa accessions. We performed genome-wide association studies (GWAS) from 917 P. trichocarpa accessions and expression-based quantitative trait loci (eQTL) analyses to identify key regulators. The GWAS and eQTL analyses resolved an overlapped interval encompassing a hydroxycinnamoyl-CoA:shikimate hydroxycinnamoyl transferase 2 (PtHCT2) that was significantly associated with CGA and partially characterized metabolite abundances. PtHCT2 leaf expression was significantly correlated with CGA abundance and it was regulated by cis-eQTLs containing W-box for WRKY binding. Among all nine PtHCT homologs, PtHCT2 is the only one that responds to infection by the fungal pathogen Sphaerulina musiva (a Populus pathogen). Validation using protoplast-based transient expression system suggests that PtHCT2 is regulated by the defense-responsive WRKY. These results are consistent with reports of CGA functioning as an antioxidant in response to biotic stress. This study provides insights into data-driven and omics-based inference of gene function in woody species.