Evaluation of Brown Midrib Sorghum Mutants as a Potential Biomass Feedstock for 2,3-Butanediol Biosynthesis

Enabling Lignin Valorization Through Integrated Advances in Plant Biology and Biorefining

Despite lignin having long been viewed as an impediment to the processing of biomass for the production of paper, biofuels, and high-value chemicals, the valorization of lignin to fuels, chemicals, and materials is now clearly recognized as a critical element for the lignocellulosic bioeconomy. However, the intended application for lignin will likely require a preferred lignin composition and form. To that end, effective lignin valorization will require the integration of plant biology, providing optimal feedstocks, with chemical process engineering, providing efficient lignin transformations. Recent advances in our understanding of lignin biosynthesis have shown that lignin structure is extremely diverse and potentially tunable, while simultaneous developments in lignin refining have resulted in the development of several processes that are more agnostic to lignin composition. Here, we review the interface between in planta lignin design and lignin processing and discuss the advances necessary for lignin valorization to become a feature of advanced biorefining.

Biomass and Bioenergy Potential of Brown Midrib Sweet Sorghum Germplasm

Public appetite for fossil fuels continues to drive energy prices and foment the build-up of intractable environmental problems. Ethanol (ETOH) production from lignocellulosic biomass grown in marginal lands offers a sustainable alternative without diverting arable land from food and feed production. The quantity and quality of lignocellulosic biomass can be enhanced by the abundant genetic diversity for biomass production as well as stem sugar and lignin composition in sorghum (Sorghum bicolor L. Moench). The objective of this study was to assess yield and quality of lignocellulosic biomass enhancement for ethanol production potential in a population of sorghum derived from two cultivars with contrasting biomass yield and compositional traits. We tested 236 recombinant inbred lines (RIL) of sorghum in a randomized complete block design (RCBD) with two replications for lignocellulosic biomass performance and determined hemicellulose, cellulose and lignin concentrations through detergent fiber analysis (DFA). The stover compositional values were used to estimate theoretical ethanol yield (ETOH on a mass basis) and production (ETOH on an area basis). Results showed that RIL carrying the brown midrib mutation had significantly higher theoretical glucose recovery (released glucose from cellulose, > 200 g kg^-1). Those carrying both mutations, had high theoretical ethanol yield (>400 L ton^-1) and high theoretical ethanol production (>14,500 L ha^-1). Lignin concentration was determined as most reliable predictor (R² = 0.67) for glucose recovery. Lignin and stem sugar concentrations (R² = 0.46 and 0.35, respectively) were good predictors for ethanol yield. Stover yield traits (R² = 0.89) were most important determinants for ethanol production. Our findings suggest that careful breeding of sorghum for genetic enhancement of biomass quantity and quality could double lignocellulosic ethanol yields.

Integration of renewable deep eutectic solvents with engineered biomass to achieve a closed-loop biorefinery

Despite the enormous potential shown by recent biorefineries, the current bioeconomy still encounters multifaceted challenges. To develop a sustainable biorefinery in the future, multidisciplinary research will be essential to tackle technical difficulties. Herein, we leveraged a known plant genetic engineering approach that results in aldehyde-rich lignin via down-regulation of cinnamyl alcohol dehydrogenase (CAD) and disruption of monolignol biosynthesis. We also report on renewable deep eutectic solvents (DESs) synthesized from phenolic aldehydes that can be obtained from CAD mutant biomass. The transgenic Arabidopsis thaliana CAD mutant was pretreated with the DESs and showed a twofold increase in the yield of fermentable sugars compared with wild type (WT) upon enzymatic saccharification. Integrated use of low-recalcitrance engineered biomass, characterized by its aldehyde-type lignin subunits, in combination with a DES-based pretreatment, was found to be an effective approach for producing a high yield of sugars typically used for cellulosic biofuels and biobased chemicals. This study demonstrates that integration of renewable DES with plant genetic engineering is a promising strategy in developing a closed-loop process.