Addressing the need for alternative transportation fuels: The Joint BioEnergy Institute
ABSTRACT Today, carbon-rich fossil fuels, primarily oil, coal, and natural gas, provide 85% of the energy consumed in the U.S. As world demand increases, oil reserves may become rapidly depleted. Fossil fuel use increases CO emissions and raises the risk of global warming. The high energy content of liquid hydrocarbon fuels makes them the preferred energy source for all modes of transportation. In the U.S. alone, transportation consumes >13.8 million barrels of oil per day and generates 0.5 gigatons of carbon per year. This release of greenhouse gases has spurred research into alternative, nonfossil energy sources. Among the options (nuclear, concentrated solar thermal, geothermal, hydroelectric, wind, solar, and biomass), only biomass has the potential to provide a high-energy-content transportation fuel. Biomass is a renewable resource that can be converted into carbon-neutral transporation fuels. Currently, biofuels such as ethanol are produced largely from grains, but there is a large, untapped resource (estimated at more than a billion tons per year) of plant biomass that could be utilized as a renewable, domestic source of liquid fuels. Well-established processes convert the starch content of the grain into sugars that can be fermented to ethanol. The energy efficiency of starch-based biofuels is however not optimal, while plant cell walls (lignocellulose) represent a huge untapped source of energy. Plant-derived biomass contains cellulose, which is more difficult to convert to sugars; hemicellulose, which contains a diversity of carbohydrates that have to be efficiently degraded by microorganisms to fuels; and lignin, which is recalcitrant to degradation and prevents cost-effective fermentation. The development of cost-effective and energy-efficient processes to transform lignocellulosic biomass into fuels is hampered by significant roadblocks, including the lack of specifically developed energy crops, the difficulty in separating biomass components, low activity of enzymes used to deconstruct biomass, and the inhibitory effect of fuels and processing byproducts on organisms responsible for producing fuels from biomass monomers. The Joint BioEnergy Institute (JBEI) is a U.S. Department of Energy (DOE) Bioenergy Research Center that will address these roadblocks in biofuels production. JBEI draws on the expertise and capabilities of three national laboratories (Lawrence Berkeley National Laboratory (LBNL), Sandia National Laboratories (SNL), and Lawrence Livermore National Laboratory (LLNL)), two leading U.S. universities (University of California campuses at Berkeley (UCB) and Davis (UCD)), and a foundation (Carnegie Institute for Science, Stanford) to develop the scientific and technological base needed to convert the energy stored in lignocellulose into transportation fuels and commodity chemicals. Established scientists from the participating organizations are leading teams of researchers to solve the key scientific problems and develop the tools and infrastructure that will enable other researchers and companies to rapidly develop new biofuels and scale production to meet U.S. transportation needs and to develop and rapidly transition new technologies to the commercial sector. JBEI's biomass-to-biofuels research approach is based in three interrelated scientific divisions and a technologies division. The Feedstocks Division will develop improved plant energy crops to serve as the raw materials for biofuels. The Deconstruction Division will investigate the conversion of this lignocellulosic plant material to sugar and aromatics. The Fuels Synthesis Division will create microbes that can efficiently convert sugar and aromatics into ethanol and other biofuels. JBEI's cross-cutting Technologies Division will develop and optimize a set of enabling technologies including high-throughput, chipbased, and omics platforms; tools for synthetic biology; multi-scale imaging facilities; and integrated data analysis to support and integrate JBEI's scientific program.
Full-textDOI: · Available from: Blake A Simmons, Jul 29, 2015
- SourceAvailable from: Manfred Auer
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- "The main contributors to the high cost of cell wall–derived glucose are low sugar density of the biomass, cell wall recalcitrance to enzymatic hydrolysis and medium content in cellulose. Each factor either impacts transportation or requires intensive use of energy and chemicals for processing (Blanch et al., 2008; Klein-Marcuschamer et al., 2010; Searcy et al., 2007). Therefore, enhancement of polysaccharide accumulation in raw biomass and improvement of biomass digestibility will have important beneficial impacts on the cost of lignocellulosic biofuels production (Blanch et al., 2011; Klein-Marcuschamer et al., 2010). "
ABSTRACT: Lignocellulosic biomass was used for thousands of years as animal feed and is now considered a great sugar source for biofuels production. It is composed mostly of secondary cell walls built with polysaccharide polymers that are embedded in lignin to reinforce the cell wall structure and maintain its integrity. Lignin is the primary material responsible for biomass recalcitrance to enzymatic hydrolysis. During plant development, deep reductions of lignin cause growth defects and often correlate with the loss of vessel integrity that adversely affects water and nutrient transport in plants. The work presented here describes a new approach to decrease lignin content while preventing vessel collapse and introduces a new strategy to boost transcription factor expression in native tissues. We used synthetic biology tools in Arabidopsis to rewire the secondary cell network by changing promoter-coding sequence associations. The result was a reduction in lignin and an increase in polysaccharide depositions in fibre cells. The promoter of a key lignin gene, C4H, was replaced by the vessel-specific promoter of transcription factor VND6. This rewired lignin biosynthesis specifically for vessel formation while disconnecting C4H expression from the fibre regulatory network. Secondly, the promoter of the IRX8 gene, secondary cell wall glycosyltransferase, was used to express a new copy of the fibre transcription factor NST1, and as the IRX8 promoter is induced by NST1, this also created an artificial positive feedback loop (APFL). The combination of strategies-lignin rewiring with APFL insertion-enhances polysaccharide deposition in stems without over-lignifying them, resulting in higher sugar yields after enzymatic hydrolysis.Plant Biotechnology Journal 11/2012; 11(3). DOI:10.1111/pbi.12016 · 5.68 Impact Factor
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- "The Golgi also plays a defining role in the secretory pathway, determining the destination of proteins, lipids, and complex carbohydrates to the cell wall and other organelles (Matheson et al., 2006; Nanjo et al., 2006). Recent years have seen a surge of interest in this area as the importance of the cell wall as a substrate for cellulosic biofuels has been recognized (Blanch et al., 2008). Efficient breakdown of the plant cell wall is an important objective in the manipulation of cell wall biosynthetic pathways. "
ABSTRACT: The plant Golgi plays a pivotal role in the biosynthesis of cell wall matrix polysaccharides, protein glycosylation, and vesicle trafficking. Golgi-localized proteins have become prospective targets for reengineering cell wall biosynthetic pathways for the efficient production of biofuels from plant cell walls. However, proteomic characterization of the Golgi has so far been limited, owing to the technical challenges inherent in Golgi purification. In this study, a combination of density centrifugation and surface charge separation techniques have allowed the reproducible isolation of Golgi membranes from Arabidopsis (Arabidopsis thaliana) at sufficiently high purity levels for in-depth proteomic analysis. Quantitative proteomic analysis, immunoblotting, enzyme activity assays, and electron microscopy all confirm high purity levels. A composition analysis indicated that approximately 19% of proteins were likely derived from contaminating compartments and ribosomes. The localization of 13 newly assigned proteins to the Golgi using transient fluorescent markers further validated the proteome. A collection of 371 proteins consistently identified in all replicates has been proposed to represent the Golgi proteome, marking an appreciable advancement in numbers of Golgi-localized proteins. A significant proportion of proteins likely involved in matrix polysaccharide biosynthesis were identified. The potential within this proteome for advances in understanding Golgi processes has been demonstrated by the identification and functional characterization of the first plant Golgi-resident nucleoside diphosphatase, using a yeast complementation assay. Overall, these data show key proteins involved in primary cell wall synthesis and include a mixture of well-characterized and unknown proteins whose biological roles and importance as targets for future research can now be realized.Plant physiology 03/2012; 159(1):12-26. DOI:10.1104/pp.111.193151 · 7.39 Impact Factor
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- "Development of efficient processes for converting renewable lignocellulosic biomass into biofuels requires microorganisms that produce target biofuels such as ethanol at high yields, titers, and productivities (Blanch et al., 2008). It is a challenging task to engineer microorganisms to perform well in the presence of compounds derived from biomass hydrolyzates, which typically contain mixtures of hexoses and pentoses together with inhibitors such as organic acids (e.g., ferulic acid, acetic acid), furan derivatives (e.g., furfural, hydroxymethylfurfural), and phenolic compounds. "
ABSTRACT: Ethanol toxicity and its effect on ethanol production by the recombinant ethanologenic Escherichia coli strain KO11 were investigated in batch and continuous fermentation. During batch growth, ethanol produced by KO11 reduced both the specific cell growth rate (micro) and the cell yield (Y(X/S)). The extent of inhibition increased with the production of both acetate and lactate. Subsequent accumulation of these metabolites and ethanol resulted in cessation of cell growth, redirection of metabolism to reduce ethanol production, and increased requirements for cell maintenance. These effects were found to depend on both the glycolytic flux and the flux from pyruvate to ethanol. Pyruvate decarboxylase (Pdc) and alcohol dehydrogenase (Adh) activities measured during the batch fermentation suggested that decreased ethanol production resulted from enzyme inhibition rather than down-regulation of genes in the ethanol-producing pathway. Ethanol was added in continuous fermentation to provide an ethanol concentration of either 17 or 27 g/L, triggering sustained oscillations in the cell growth rate. Cell concentrations oscillated in-phase with ethanol and acetate concentrations. The amplitude of oscillations depended on the concentration of ethanol in the fermentor. Through multiple oscillatory cycles, the yield (Y(P/S)) and concentration of ethanol decreased, while production of acetate increased. These results suggest that KO11 favorably adapted to improve growth by synthesizing more ATP though acetate production, and recycling NADH by producing more lactate and less ethanol. Implications of these results for strategies to improve ethanol production are described.Biotechnology and Bioengineering 08/2010; 106(5):721-30. DOI:10.1002/bit.22743 · 4.16 Impact Factor