Consolidated bioprocessing of cellulosic biomass: an update.
TL;DR: Progress in developing CBP-enabling microorganisms is being made through two strategies: engineering naturally occurring cellulolytic microorganisms to improve product-related properties, such as yield and titer, and engineering non-cellulolytic organisms that exhibit high product yields and titers to express a heterologous cellulase system enabling cellulose utilization.
About: This article is published in Current Opinion in Biotechnology.The article was published on 2005-10-01. It has received 1408 citations till now. The article focuses on the topics: Cellulase & Lignocellulosic biomass.
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TL;DR: An up-to-date review of the literature available on the subject of liquid bio-fuels can be found in this article, which includes information based on the research conducted globally by scientists according to their local socio-cultural and economic situations.
1,948 citations
Cites background from "Consolidated bioprocessing of cellu..."
...A few microbial species such as Neurospora, Monilia, Paecilomyces and Fusarium have been reported to hold the ability to ferment cellulose directly to ethanol by simultaneous saccharification and fermentation (SSF) [100]....
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...Several methods have been developed to reduce the inhibition, including the use of high concentrations of enzymes, the supplementation of b-glucosidases during hydrolysis and removal of sugars during hydrolysis by ultrafiltration or SSF [102,103]....
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TL;DR: A survey of biomass pret treatment technologies with emphasis on concepts, mechanism of action and practicability, and the potential for industrial applications of different pretreatment technologies are the highlights of this paper.
1,618 citations
Cites background from "Consolidated bioprocessing of cellu..."
...These microorganisms thrive on cellulodextrins, but exhibit limited growth in the presence of sugar monomer substrates such as glucose (Lynd et al. 2005; Zhang and Lynd 2005)....
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TL;DR: In this paper, the authors review quantitative cellulase activity assays using soluble and insoluble substrates, and focus on their advantages and limitations, and hypothesize that continuous culture using insoluble cellulosic substrates could be a powerful selection tool for enriching beneficial cellulase mutants from the large library displayed on the cell surface.
1,495 citations
TL;DR: This review gives an overview of the new technologies required and the advances achieved in recent years to bring lignocellulosic ethanol towards industrial production.
1,477 citations
Cites methods from "Consolidated bioprocessing of cellu..."
...Further process integration can be achieved by performing both hydrolysis and fermentation in a single reactor, using one or a mixture of microorganisms that produce all the required enzymes and ferment all sugars ‐ so-called consolidated bioprocessing (CBP) [ 64 ]....
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TL;DR: In this article, a review of available technologies for bioethanol production from agricultural wastes is discussed, which can increase concentrations of fermentable sugars after enzymatic saccharification, thereby improving the efficiency of the whole process.
1,432 citations
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TL;DR: A concluding discussion identifies unresolved issues pertaining to microbial cellulose utilization, suggests approaches by which such issues might be resolved, and contrasts a microbially oriented cellulose hydrolysis paradigm to the more conventional enzymatically oriented paradigm in both fundamental and applied contexts.
Abstract: Fundamental features of microbial cellulose utilization are examined at successively higher levels of aggregation encompassing the structure and composition of cellulosic biomass, taxonomic diversity, cellulase enzyme systems, molecular biology of cellulase enzymes, physiology of cellulolytic microorganisms, ecological aspects of cellulase-degrading communities, and rate-limiting factors in nature. The methodological basis for studying microbial cellulose utilization is considered relative to quantification of cells and enzymes in the presence of solid substrates as well as apparatus and analysis for cellulose-grown continuous cultures. Quantitative description of cellulose hydrolysis is addressed with respect to adsorption of cellulase enzymes, rates of enzymatic hydrolysis, bioenergetics of microbial cellulose utilization, kinetics of microbial cellulose utilization, and contrasting features compared to soluble substrate kinetics. A biological perspective on processing cellulosic biomass is presented, including features of pretreated substrates and alternative process configurations. Organism development is considered for "consolidated bioprocessing" (CBP), in which the production of cellulolytic enzymes, hydrolysis of biomass, and fermentation of resulting sugars to desired products occur in one step. Two organism development strategies for CBP are examined: (i) improve product yield and tolerance in microorganisms able to utilize cellulose, or (ii) express a heterologous system for cellulose hydrolysis and utilization in microorganisms that exhibit high product yield and tolerance. A concluding discussion identifies unresolved issues pertaining to microbial cellulose utilization, suggests approaches by which such issues might be resolved, and contrasts a microbially oriented cellulose hydrolysis paradigm to the more conventional enzymatically oriented paradigm in both fundamental and applied contexts.
4,769 citations
TL;DR: The results suggest that the effectiveness of microbial fuel cells can be increased with organisms such as G. sulfurreducens that can attach to electrodes and remain viable for long periods of time while completely oxidizing organic substrates with quantitative transfer of electrons to an electrode.
Abstract: Previous studies have suggested that members of the Geobacteraceae can use electrodes as electron acceptors for anaerobic respiration. In order to better understand this electron transfer process for energy production, Geobacter sulfurreducens was inoculated into chambers in which a graphite electrode served as the sole electron acceptor and acetate or hydrogen was the electron donor. The electron-accepting electrodes were maintained at oxidizing potentials by connecting them to similar electrodes in oxygenated medium (fuel cells) or to potentiostats that poised electrodes at +0.2 V versus an Ag/AgCl reference electrode (poised potential). When a small inoculum of G. sulfurreducens was introduced into electrode-containing chambers, electrical current production was dependent upon oxidation of acetate to carbon dioxide and increased exponentially, indicating for the first time that electrode reduction supported the growth of this organism. When the medium was replaced with an anaerobic buffer lacking nutrients required for growth, acetate-dependent electrical current production was unaffected and cells attached to these electrodes continued to generate electrical current for weeks. This represents the first report of microbial electricity production solely by cells attached to an electrode. Electrode-attached cells completely oxidized acetate to levels below detection (<10 micro M), and hydrogen was metabolized to a threshold of 3 Pa. The rates of electron transfer to electrodes (0.21 to 1.2 micro mol of electrons/mg of protein/min) were similar to those observed for respiration with Fe(III) citrate as the electron acceptor (E(o)' =+0.37 V). The production of current in microbial fuel cell (65 mA/m(2) of electrode surface) or poised-potential (163 to 1,143 mA/m(2)) mode was greater than what has been reported for other microbial systems, even those that employed higher cell densities and electron-shuttling compounds. Since acetate was completely oxidized, the efficiency of conversion of organic electron donor to electricity was significantly higher than in previously described microbial fuel cells. These results suggest that the effectiveness of microbial fuel cells can be increased with organisms such as G. sulfurreducens that can attach to electrodes and remain viable for long periods of time while completely oxidizing organic substrates with quantitative transfer of electrons to an electrode.
2,133 citations
"Consolidated bioprocessing of cellu..." refers background in this paper
...synthesis gas and animal wastes), sunlight [3,4], inorganic compounds [5 ], and fossil resources (e....
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...Energy carriers that can be made from these resources include organic fuels, electricity [4,5 ] and hydrogen [3]....
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TL;DR: It is concluded that a broad range of intensive research and development is urgently needed to produce technological options that can allow both climate stabilization and economic development.
Abstract: Stabilizing the carbon dioxide-induced component of climate change is an energy problem. Establishment of a course toward such stabilization will require the development within the coming decades of primary energy sources that do not emit carbon dioxide to the atmosphere, in addition to efforts to reduce end-use energy demand. Mid-century primary power requirements that are free of carbon dioxide emissions could be several times what we now derive from fossil fuels (approximately 10(13) watts), even with improvements in energy efficiency. Here we survey possible future energy sources, evaluated for their capability to supply massive amounts of carbon emission-free energy and for their potential for large-scale commercialization. Possible candidates for primary energy sources include terrestrial solar and wind energy, solar power satellites, biomass, nuclear fission, nuclear fusion, fission-fusion hybrids, and fossil fuels from which carbon has been sequestered. Non-primary power technologies that could contribute to climate stabilization include efficiency improvements, hydrogen production, storage and transport, superconducting global electric grids, and geoengineering. All of these approaches currently have severe deficiencies that limit their ability to stabilize global climate. We conclude that a broad range of intensive research and development is urgently needed to produce technological options that can allow both climate stabilization and economic development.
1,396 citations
"Consolidated bioprocessing of cellu..." refers background in this paper
...New applications of emerging technologies will be required to respond to these challenges [1,2 ]....
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TL;DR: Ethanol produced from cellulosic biomass is examined as a large-scale transportation fuel and a cost-competitive process appears possible in a decade, with conversion economics the key obstacle to be overcome.
Abstract: Ethanol produced from cellulosic biomass is examined as a large-scale transportation fuel. Desirable features include ethanol's fuel properties as well as benefits with respect to urban air quality, global climate change, balance of trade, and energy security. Energy balance, feedstock supply, and environmental impact considerations are not seen as significant barriers to the widespread use of fuel ethanol derived from cellulosic biomass. Conversion economics is the key obstacle to be overcome. In light of past progress and future prospects for research-driven improvements, a cost-competitive process appears possible in a decade.
896 citations
TL;DR: This strain efficiently fermented both glucose and xylose, which is essential for economical conversion of lignocellulosic biomass to ethanol, and achieved through a combination of the pentose phosphate and Entner-Doudoroff pathways.
Abstract: The ethanol-producing bacterium Zymomonas mobilis was metabolically engineered to broaden its range of fermentable substrates to include the pentose sugar xylose. Two operons encoding xylose assimilation and pentose phosphate pathway enzymes were constructed and transformed into Z. mobilis in order to generate a strain that grew on xylose and efficiently fermented it to ethanol. Thus, anaerobic fermentation of a pentose sugar to ethanol was achieved through a combination of the pentose phosphate and Entner-Doudoroff pathways. Furthermore, this strain efficiently fermented both glucose and xylose, which is essential for economical conversion of lignocellulosic biomass to ethanol.
835 citations
"Consolidated bioprocessing of cellu..." refers background in this paper
...mobilis [46] able to ferment xylose to ethanol were developed in the 1990s....
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