Research Highlights

Turning bioenergy crops into fuels and other products requires breaking down the complex mixture of polysaccharides found in plant material. Glycoside hydrolase family 5 (GH5) is a large and diverse family of enzymes able to digest a wide range of polysaccharides. Researchers at the Great Lakes Bioenergy Research Center (GLBRC) described the functional diversity of members of a GH5 subfamily to explore the structural origins of their broad substrate specificity, a step toward engineering better enzymes for converting biomass into biofuels and other specialty bioproducts.

Characterizing microbial strategies for lignin breakdown is important for understanding plant biomass turnover in nature, and could aid in developing industrial systems for producing commodity chemicals from this abundant renewable resource. In this report, Great Lakes Bioenergy Research Center researchers provide new information on the pathway used by sphingomonad bacteria to cleave the β-aryl ether bond commonly found in lignin. Specifically, they report on a previously uncharacterized heterodimeric β-etherase enzyme, with unique properties, from Novosphingobium aromaticivorans and other sphingomonads.

Nitrous oxide (N2O) is a potent greenhouse gas and major component of the net global warming potential of bioenergy crops. Numerous environmental factors influence soil N2O production, making direct correlation difficult to any one factor under field conditions.

The organic matter left over after biofuel production is a rich potential feedstock for making additional high-value bioproducts. GLBRC researchers previously described a small-scale bioreactor that used a mixed microbial community to produce valuable molecules from the conversion residue remaining after lignocellulosic ethanol production. The team has now analyzed the composition and metabolic characteristics of the microbiome as a step toward understanding how to engineer and control microbial communities to optimize production of medium-chain fatty acids (MCFAs), which can be used to make a variety of industrial chemicals and pharmaceuticals.

With the goal of ultimately engineering bioenergy crops to accumulate large amounts of easily digestible sugars, researchers from the Great Lakes Bioenergy Research Center (GLBRC) have identified a transcription factor that is highly co-expressed with the major mixed-linkage glucan (MLG) synthase gene in the model grass Brachypodium distachyon. Characterization of downstream genes regulated by this transcription factor provides insight into the mechanism of MLG production and restructuring, information vital to overcoming known growth defects associated with MLG synthase overexpression.

The iron-binding molecule pulcherrimin was described 65 years ago, but the genes responsible for its production in budding yeasts remained uncharacterized. Genomic comparisons across 90 species of the budding yeast subphylum Saccharomycotina revealed a four-gene cluster associated with pulcherrimin production, and targeted gene disruptions in Kluyveromyces lactis revealed likely functions for each of the genes: two biosynthetic enzymes, a transporter, and a putative transcription factor.

Recent advancements from the lignin biosynthetic research community provide a greater understanding of lignin composition and structure, including revelations about new, previously unknown components of the lignin polymer; this makes it possible to imagine what features an “ideal lignin” might have. In this collaborative study, GLBRC researchers and their colleagues describe the ideal nature of catechyl lignin (C-lignin) via a revised compositional characterization, advantageous features in regard to reactivity and stability, and their successful attempt to convert C-lignin polymers to monomers in near-quantitative yields.

This holistic biomass-to-wheels analysis showed that, contrary to conventional wisdom, seeking atom-economical biomass-to-fuel strategies may not necessarily be the optimal objective towards the development of the next generation biofuels. In addition to carbon yield, the study identified the energy requirements of the process and the resulting biofuel type and quality to be key factors that should be considered simultaneously in the selection of alternative biofuels and development of new biofuel strategies.

In this study, researchers examined natural diverse isolates of Saccaromyces cerevisiae for tolerance to ILs and identified two genes associated with this outcome. Analysis of specific gene variants suggests that tolerance may be governed in part by the degree to which ILs can be pumped out of cells.

Bioenergy cropping systems can act as sinks or sources of atmospheric carbon dioxide, depending on the balance between the formation and decomposition of organic carbon.