Great Lakes Bioenergy research consistently results in new discoveries and new technologies. Here, we highlight high-impact research from all three of our research areas.
As a feedstock for biomass-to-biofuel processes, woody biomass exhibits several advantages that facilitate logistics relative to herbaceous feedstocks, including year-round availability and high bulk density. As we envision biomass-to-biofuel processes that include diverse biomass feedstocks, the physical and chemical properties of said biomass will have an important impact on the conversion process.
In order to determine the structural basis for stereospecificity of bacterial enzymes involved in lignin bond cleavage, crystal structures of the enzymes involved were solved and the corresponding biochemical analyses for these proteins were performed. The detailed structural and biochemical characterization of LigE and LigF in this study,1 and the corresponding detailed structural and biochemical characterization of other members of this lignin degradation pathway (LigD, LigO, LigL, and LigG) in a second study,2 reveal important new aspects of the enzyme mechanisms and the determinants of substrate specificity.
To gain insight into how Bayberry fruits produce the highest amount of surface lipid known in nature, the authors examined the chemical and morphological development of the Bayberry wax layer, monitored its biosynthesis through radiolabeling studies, and identified transcripts for enzymes and proteins expressed during Bayberry surface wax production. The biochemical and expression data together indicate that Bayberry surface glycerolipids are synthesized by a pathway for triacylglycerol synthesis that is related to cutin biosynthesis, rather than conventional triacylglycerol assembly.
Mechanism of imidazolium ionic liquids toxicity in saccharomyces cerevisiae and rational engineering of a tolerant, xylose-fermenting strain
The method to deconstruct lignocellulosic biomass using ionic liquids (ILs) is a promising technology that can bypass expensive enzymatic pretreatments that are commonly used. A potential limitation to adoption of ILs for bioconversion is that residual IL solvent is toxic to microbes and can impede fermentation of biomass to biofuels. A technique called chemical genomics was used to identify yeast genes that confer sensitivity or resistance to IL, allowing researchers to identify a cellular substructure called the mitochondrion as the apparent target of IL toxicity. Targeted deletion of a gene identified from the chemical genomics screen in a xylose-fermenting strain of yeast greatly increased its IL tolerance, biomass-derived sugar conversion, and yields of ethanol.
Use of nanostructure-initiator mass spectrometry (NIMS) to deduce selectivity of reaction in glycoside hyrolases
The enzymatic hydrolysis of plant cell wall material is a formidable task due to its complexity. Enzyme cocktails containing multiple classes of polysaccharide-degrading enzymes are used in several existing cellulosic ethanol plants to hydrolyze plant biomass into fermentable sugars. These enzymes are classified into families in the carbohydrate active enzyme (CAZy) database, and they include glycoside hydrolases (GHs), pectic lyases (PLs), carbohydrate esterases (CEs), and others. Due to several experimental limitations, only a small fraction of the enzymes included in CAZy have a function assigned by biochemical analysis.
Lignin, a complex polyphenolic constituent of plant secondary cell walls, is one of the most abundant biopolymers on the planet and is an immensely important global carbon sink. The chemical recalcitrance of lignin, however, poses a major challenge for industrial biomass processing, most notably in pulp and paper production and in the emerging cellulosic biofuels industry.
Valorization of lignin from biomass is challenging and research efforts have lagged behind the upgrading of sugar streams. Yet lignin comprises a substantial portion of lignocellulosic biomass (15-30% by weight), is the most energy dense fraction, and is a rich source of aromatic compounds.
A valuable ‘new’ compound is available from lignin ‘waste’ streams. Lignin, a complex phenylpropanoid polymer in the plant cell wall, is synthesized via oxidative radical coupling reactions from three prototypical monolignols. Several novel monomers, all deriving from the monolignol biosynthetic pathway, have been found to incorporate into lignin in wild-type and transgenic plants; these findings imply that plants are quite flexible in being able to use a variety of monomers during lignification to form the heterologous lignin polymer.
Soil microbial communities are an important component of ecosystems because of their key roles in nutrient cycling, influence on plant community composition, regulation of plant productivity, and decomposition of organic matter. The recovery of these communities is an important element in the process of returning a restored ecosystem to its desired structure and function, but this recovery often lags behind changes in land use and management.
The recalcitrance of plant cell walls to biological degradation, deconstruction, or conversion is the most critical challenge in developing successful bioprocessing technologies for lignocellulose conversion to renewable fuels and chemicals.