May 01, 2017
New Insights On Recalcitrance From Lignin Inhibition Of Microbial Deconstruction
Microbial solubilization of biomass selectively targets carbohydrates. Clostridium thermocellum, a highly effective cellulolytic microbe, can hydrolyze ~93% of 100gL-1 pure cellulose. The microbe solubilizes only partially hydrolyzes cellulose in untreated energy crops. Techniques used were quantitative fluorescence colocalization analysis and surface chemical imaging. Quantitative evidence for the cause of feedstock recalcitrance: depletion of surface carbohydrate increases lignin exposure which leads to inhibition of enzymatic activity, while the bulk residual biomass retains significant undigested sugar content. Limited hydrolysis is not caused by inhibitory hydrolyzed sugars nor fermentation products (i.e., ethanol).
April 17, 2017
Photos of the field experiments in the first (2013), second (2014), and third (2015) growing seasons (...more)
Multi-Year Study Of Transgenic Switchgrass Plants In Regulation Shows Improved Yield And Dependency On Expression Levels
Four promising lines with moderate or low microRNA (miR156) overexpression from prior greenhouse study were selected for a field experiment to assess miR156 expression levels and biomass yields over three years. The best performing line consistently produced more biomass (25-56%) than the control in all three seasons, which translated to the production of 30% more biofuel per plant in the final season. Transgenic plants with modifications to transcriptional regulators, which impact such a broad range of genes, will likely require more extensive field evaluations than those with single and simple trait gene modifications to evaluate the stability of the desired growth phenotypes.
April 12, 2017
First-Of-A-Kind Study Of Thermophilic CBP With Cotreatment
Milling during lignocellulosic fermentation (or cotreatment) is an alternative to thermochemical pretreatment to enhance biological solubilization of lignocellulose. Carbohydrate solubilization was measured in consolidated bioprocessing with Clostridium thermocellum with cotreatment or with hydrothermal pretreatment. High carbohydrate solubilization was demonstrated without thermochemical pretreatment and added saccharolytic enzymes. C. thermocellum appears able to attack all the major linkages in cellulosic biomass provided that these linkages are accessible. The ability of C. thermocellum to withstand high intensity milling supports the feasibility of cotreatment. Less modified lignin may foster production of value-added coproducts.
March 27, 2017
Use of Caldicellulosiruptor saccharolyticus as a biological probe to report on changes in recalcitrance of plant biomass
C. saccharolyticus whole genome microarrays were used to access the transcriptome when grown on purified polysaccharides and chemically pretreated or genetically modified lignocellulosic substrates. Differential regulation of carbohydrate degradation, transport, and metabolism genes in C. saccharolyticus can be used to assess the availability of various plant polysaccharides to the microbe. This allows for inferences about the consequences of a chemical pretreatment or genetic modification of lignocellulose with an eye towards biofuels production.
March 21, 2017
Improving Pretreatment Inhibitor Tolerance in Clostridium thermocellum
Bioconversion performance in the presence of common pretreatment inhibitors was improved through targeted strain engineering thus reducing barriers to achieving a robust consolidated bioprocessing strategy with Clostridium thermocellum.
March 21, 2017
CBP-CT: an R&D-Driven Innovation with Potential for Disruptive Reductions in the Cost of Cellulosic Biofuels
Compared to current technology, the CBT-CT scenario was projected to offer 4.6-fold greater annual revenue, as well as 8-fold shorter payback period, and feasibility at ~10-fold smaller scale. CBT-CT is a potentially disruptive technology and a powerful, though still speculative, example of the potential benefits of including new-paradigm as well as in-paradigm innovation in R&D portfolios.
March 18, 2017
Overexpression of DUF266 can significantly enhance both cellulose and biomass in Populus
(BESC's 900th publication)
Little is known about the function of Domain of Unknown Function 266 (DUF266)-containing proteins and no DUF266 protein has been characterized in Populus. A bioinformatics approach was taken to identify all DUF266 proteins in Populus and their relationship with their homologs in other species. A transgenic approach was used to determine the function of one member of DUF266 proteins in Populus (PdDUF266A). The resulting phenotypes make PdDUF266A a promising target for genetic manipulation for improving biomass quality.
March 10, 2017
Use of Photoacoustic AFM to Spatially Resolve Nanomechanics of Plant Cell Wall Delignification
By chemically processing biomass and employing emerging nanometrology techniques, the various stages of lignin removal may be distinguished through the observation of morphochemical and nanomechanical variations. The cell wall nanomechanical properties undergo quantifiable reductions in plasticity, adhesion energy, and elasticity. These quantitative observations can be used to characterize delignification. The observed reduction in plasticity seems counterintuitive considering that lignin adds to cell wall rigidity.
February 27, 2017
Microbial Attachment to Cellulose Substrate Produces Widespread Gene Expression Changes
Unlike the majority of biofilm forming bacteria, C. thermocellum adheres to substrata that also provide its major carbon and energy sources. Before this study, discrete omics analyses of biofilm and planktonic cell populations had not been performed. Cellulolytic bacterial cells that evolved to thrive on solid carbon sources were shown to thoroughly alter expression of their central metabolism, anabolism, and homeostatic functions in response to the availability of solid attachment interfaces and solubilizable carbohydrates. The attached bacteria were functionally strong in growth and biomass conversion, while the planktonic cells were stressed and motile due to low available substrates.
February 07, 2017
Understanding the role of pentose sugars on C. thermocellum metabolism
This work highlights the importance of removing pentose sugars during bioconversion to biofuels, which could be achieved with C5 utilizing co-cultures or engineered strains of C. thermocellum, and is the first report of a functional ArgD-type cell signaling system in a thermophilic Firmicute and further work is warranted to understand the role of cell-to-cell signaling in achieving robust fermentations of lignocellulosic biomass.
January 20, 2017
Visualization of Significant Alteration of Populus biomass by C. bescii
Caldicellulosiruptor bescii targets surface cellulose and hemicellulose, but increase of surface lignin could inhibit further sugar access. Biphasic cell growth is attributed to degradation of easily accessible sugars followed by utilization of more insoluble polysaccharides.
January 10, 2017
Metabolic Adaptation Of C. thermocellum To Growth Inhibitors Released During Deconstruction Of Switchgrass
Integrated omics data of microbial growth on complex lignocellulosic biomass over time provided a detailed view of the molecular machinery (metabolites and enzymes) that reveals temporal adaptation to a complex, lignocellulose substrate — information that is critical for engineering C. thermocellum's industrial efficacy.
January 03, 2017
Engineering N-terminal End of CelA Enhances the Cellulolytic Activity of Caldicellulosiruptor bescii
To test whether alteration of the N-terminal terminus of CelA GH9 and CelA GH48 domains might improve secretion and/or catalytic efficiency of CelA, repeating aspartate tags were introduced into the N-terminal ends of these 8 domains. Introduction of repeating aspartate tags resulted in an increase in the general activity of the exoproteome and a dramatic increase in growth of C. bescii on crystalline cellulose. Most efficient cellulase systems contain highly active exocellulase enzymes capable of decrystallizing cellulose, so the observed increase in activity on Avicel bears directly upon the ability of CelA to degrade realistic biomass feedstocks destined for biofuels production.