GLBRC's Publications


Our researchers consistently turn out new and innovative research that can lead to publications and new technology. On this page we'll highlight new research publications and/or activities in the GLBRC that underscore the great work that our researchers are doing.

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.   

Lignocellulosic crop residues are a promising alternative feedstock for producing liquid fuels and chemicals for modern biobased economies, and biochemical conversion of lignocellulosic biomass to liquid fuels requires pretreatment and enzymatic hydrolysis of the biomass to yield fermentable sugars. To compete with traditional refineries, biorefineries must achieve high carbohydrate-to-fuel yields with low enzymatic input and facilitate lignin valorization to co-products extending beyond simply using lignin to generate heat and power. Most pretreatment processes require high enzymatic loadings to achieve higher sugar yields under industrially-relevant conditions.

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, 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, 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.

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.

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.

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 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.

By providing mechanical strength and enabling reception and transmission of developmental and environmental cues, the plant cell wall serves as a critical interface between the protoplast and the surrounding environment.

Lignocellulose-derived hydrolysates contain several different inhibitors (collectively called lignotoxins or LTs) that arise during pre-treatment of biomass. Determining the mechanisms by which yeast or bacteria are adversely affected by LTs is a key step toward improving the efficiency of fermentation and bioconversion.

A major barrier to efficient conversion of lignocellulosic materials to biofuels is sensitivity of microbes to inhibitory compounds formed during biomass pretreatment. Aromatics derived from lignocellulose are a major class of inhibitors that are typically not metabolized by microbes commonly used as biocatalysts.

The prospect of converting large tracts of the Midwest’s marginal farming land to perennial biofuel crops carries with it some key unknowns, including how such a change could affect the balance of water between rainfall inputs, evaporation losses, and movement of soil water to the groundwater. In humid climates such as the U.S.

American crude oil imports have almost tripled since the early 1970s and now account for about half of the American petroleum supply, a dependence that is fueling climate change. Regulations intended to mitigate climate change, however, seek an 80% reduction in US greenhouse gas (GHG) emissions by 2050 in order to stabilize global GHG concentrations at low to medium levels.

Nitrous oxide (N2O) is a potent greenhouse gas and a substantial proportion of the total carbon footprint associated with feedstock production, and as bioenergy cropping systems continue to be considered, their greenhouse gas emissions will be a key component of sustainability evaluation.

Microbial communities that have symbiotic relationships with biomass insects are now recognized to be a relevant source of microbes with diverse metabolic and biosynthetic capabilities that could be used in improving the enzymatic deconstruction of biomass materials for biofuel production. Recently, a highly cellulolytic and hemicellulolytic Actinomycete, Streptomyces sp.

A recent breakthrough in lignocellulosic biomass deconstruction at Great Lakes Bioenergy Research Center utilizes γ-valerolactone (GVL), a renewable solvent that can be derived from the biomass itself. In a recent publication researchers at GLBRC designed a process for large-scale production of ethanol from lignocellulosic biomass that employs GVL for biomass deconstruction.

Non-productive binding of enzymes to lignin is thought to impede the saccharification efficiency of pretreated lignocellulosic biomass to fermentable sugars.