Research Highlights

Spent liquors from biomass pretreatment could provide a source for renewable chemical production. This study characterized the phenolics in spent liquor from aqueous ammonia pretreatment of poplar, investigated the impact of metal additives on the formation of phenolics during pretreatment, and explored valorization microbial transformation.

Scientists performed all-atom molecular dynamics simulations to study lignin solvation, solvent-mediated conformational changes, and the interaction of solvated lignin oligomers with model surfaces. They focused on the behavior of a model lignin oligomer in methanol, ethanol, a binary mixture of ethanol and water, and water alone at typical RCF reaction temperature (473 K) and room temperature. Model palladium (Pd) and carbon (C) surfaces were introduced to understand how solvent choice impacts adsorption onto a representative catalytic surface and to quantify competition among reactant and solvent molecules for surface binding sites.

Researchers are pursuing efforts to design grasses with elevated levels of cell wall carbohydrates, including mixed-linkage glucan (MLG), to improve their value as bioenergy feedstocks. By studying four grasses with varying MLG production, scientists showed that strains engineered for higher MLG production also accumulate MLG in the roots, potentially affecting soil carbon cycling.

Lignocellulosic biomass is an abundant renewable resource that could provide fuels and chemicals for a bioeconomy, but the complexity of plant cell wall structure limits its use. Treatment with environmentally safe and inexpensive deep eutectic solvents (DES) is a promising technique for recovering the three main cell wall polymers: cellulose, hemicellulose, and lignin. Research has also focused on genetic engineering to produce lignin that is easier to deconstruct. Here, scientists evaluated three engineered poplar strains with distinct lignin modifications to assess how this tailored lignin chemistry influences deconstruction and sugar release in DES-based conversion.

The plant polymer lignin is an abundant renewable source of aromatics. Chemical depolymerization yields mixtures of aromatics, including acetovanillone, a vanillin derivative with an acetyl side chain. Not all microbes that can generate chemicals from aromatics can metabolize acetovanillone, which can represent up to 10% of the aromatic monomers in deconstructed biomass. Here scientists identified a single amino acid change in a previously uncharacterized protein that is necessary and sufficient for N. aromaticivorans growth with acetovanillone as the sole organic carbon source.

The complex carbon-rich plant structure lignin can be broken down to make aviation fuel, plastics, and other commercial products. During chemical deconstruction of lignocellulosic biomass, the presence of phenolic pendant groups such as p-coumarate can improve the efficiency of deconstruction or lead to toxins that inhibit microbial fermentation of plant sugars. Though previously thought only to be in commelinid monocots, the list of pCA-containing eudicots is growing.

This work reviews the current landscape of plant genetics through the lens of bioenergy crops to present a roadmap for using DNA-based tools to engineer improvements.

Bioenergy sorghum is a drought-tolerant grass adapted low-productivity lands that promotes soil carbon stocks. An extended vegetative growth phase and long growing season produce 4-5 meter stems that account for about 80% of shoot biomass. During a typical growing season stem density increases significantly following stem internode growth. This study offers new insights on what causes it. 

This research enhances the selection and validation of upstream processing methods for lignocellulosic biomass pipeline processing, which improves economic and environmental outcomes for biorefineries, and shows the first comparison of pretreatment technique viability for oilcane.

Grasses and some tree species have naturally γ-acylated lignins. Poplar lignins have para-hydroxybenzoate groups on 1-15% of syringyl subunits. During hydrogenolysis, it is generally assumed that p-hydroxybenzoate is cleaved before the deacylated lignin is depolymerized. Here, scientists showed how the presence of a γ-acylated group alters the product portfolio produced by hydrogenolysis with palladium on carbon (Pd/C) as the catalyst.