Current Opinion in Biotechnology

We march backwards into the future.

Publication Date: 2009 Jun 25 PMID: 19560337
Authors: Jeffries, T. - Lindblad, P.
Journal: Curr Opin Biotechnol

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Engineering algae for biohydrogen and biofuel production.

Publication Date: 2009 Jun 25 PMID: 19560336
Authors: Beer, L. L. - Boyd, E. S. - Peters, J. W. - Posewitz, M. C.
Journal: Curr Opin Biotechnol

There is currently substantial interest in utilizing eukaryotic algae for the renewable production of several bioenergy carriers, including starches for alcohols, lipids for diesel fuel surrogates, and H(2) for fuel cells. Relative to terrestrial biofuel feedstocks, algae can convert solar energy into fuels at higher photosynthetic efficiencies, and can thrive in salt water systems. Recently, there has been considerable progress in identifying relevant bioenergy genes and pathways in microalgae, and powerful genetic techniques have been developed to engineer some strains via the targeted disruption of endogenous genes and/or transgene expression. Collectively, the progress that has been realized in these areas is rapidly advancing our ability to genetically optimize the production of targeted biofuels.

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Modular model-based design for heterologous bioproduction in bacteria.

Publication Date: 2009 Jun 24 PMID: 19559595
Authors: Landrain, T. E. - Carrera, J. - Kirov, B. - Rodrigo, G. - Jaramillo, A.
Journal: Curr Opin Biotechnol

We review the current status of expression of heterologous systems for bioenergy and bioproduction in bacteria using a model-based approach. As an aim for synthetic biology, it requires mathematical models of genetic modules that could be characterized independently of their context. This fastens the design of metabolic circuits using a combinatorial design approach, where given pathways could be optimized for maximal bioproduction, while being nontoxic for the chassis. We show how recent characterization of genetic parts, such as promoters, RBS or sRNAs could be used to fine-tune the expression of individual genes to achieve that goal. We also present lists of enzymes that are used for bioproduction, enlarging such set of biological parts.

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Biofuels and the conundrum of sustainability.

Publication Date: 2009 Jun 22 PMID: 19553101
Authors: Sheehan, J. J.
Journal: Curr Opin Biotechnol

Sustainable energy is the problem of the 21st century. If biofuels want to be part of the solution they must accept a degree of scrutiny unprecedented in the development of a new industry. That is because sustainability deals explicitly with the role of biofuels in ensuring the well-being of our planet, our economy, and our society both today and in the future. Life cycle assessment (LCA) has been the standard framework for assessing sustainability of biofuels. These assessments show that corn ethanol has a marginally lower fossil energy and greenhouse gas footprint compared to petroleum fuel. Sugarcane ethanol and some forms of biodiesel offer substantially lower footprints. New biofuels may offer low footprints. The science of LCA is being stretched to its limits as policy makers consider direct and indirect effects of biofuels on global land and water resources, global ecosystems, air quality, public health, and social justice.

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Yeast metabolic engineering for hemicellulosic ethanol production.

Publication Date: 2009 Jun 20 PMID: 19545992
Authors: Van Vleet, J. - Jeffries, T.
Journal: Curr Opin Biotechnol

Efficient fermentation of hemicellulosic sugars is critical for the bioconversion of lignocellulosics to ethanol. Efficient sugar uptake through the heterologous expression of yeast and fungal xylose/glucose transporters can improve fermentation if other metabolic steps are not rate limiting. Rectification of cofactor imbalances through heterologous expression of fungal xylose isomerase or modification of cofactor requirements in the yeast oxidoreductase pathway can reduce xylitol production while increasing ethanol yields, but these changes often occur at the expense of xylose utilization rates. Genetic engineering and evolutionary adaptation to increase glycolytic flux coupled with transcriptomic and proteomic studies have identified targets for further modification, as have genomic and metabolic engineering studies in native xylose fermenting yeasts.

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Energy biotechnology with cyanobacteria.

Publication Date: 2009 Jun 17 PMID: 19540103
Authors: Angermayr, S. A. - Hellingwerf, K. J. - Lindblad, P. - Teixeira de Mattos, M. J.
Journal: Curr Opin Biotechnol

The world's future energy demand calls for a sustainable alternative for the use of fossil fuels, to restrict further global warming. Harvesting solar energy via photosynthesis is one of Nature's remarkable achievements. Existing technologies exploit this process for energy 'production' via processing of, for example, part of plant biomass into ethanol, and of algal biomass into biodiesel. Fortifying photosynthetic organisms with the ability to produce biofuels directly would bypass the need to synthesize all the complex chemicals of 'biomass'. A promising way to achieve this is to redirect cyanobacterial intermediary metabolism by channeling (Calvin cycle) intermediates into fermentative metabolic pathways. This review describes this approach via the biosynthesis of fermentation end products, like alcohols and hydrogen, driven by solar energy, from water (and CO(2)).

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Lignocellulose conversion to biofuels: current challenges, global perspectives.

Publication Date: 2009 Jun 10 PMID: 19523813
Authors: Himmel, M. E. - Bayer, E. A.
Journal: Curr Opin Biotechnol

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Natural paradigms of plant cell wall degradation.

Publication Date: 2009 Jun 10 PMID: 19523812
Authors: Wei, H. - Xu, Q. - Taylor, L. E. 2nd - Baker, J. O. - Tucker, M. P. - Ding, S. Y.
Journal: Curr Opin Biotechnol

Natural processes of recycling carbon from plant cell walls are slow but very efficient, generally involving microbial communities and their secreted enzymes. Efficient combinations of microbial communities and enzymes act in a sequential and synergistic manner to degrade plant cell walls. Recent understanding of plant cell wall ultra-structure, as well as the carbon metabolism, ATP production, and ecology of participating microbial communities, and the biochemical properties of their cellulolytic enzymes have led to new perspectives on saccharification of biomass. Microbial communities are dynamic functions of the chemical and structural compositions of plant cell wall components. The primitive 'multicellularity' exhibited by certain cellulolytic microorganisms may play a role in facilitating cell-cell communication and cell-plant cell wall-substrate interaction.

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Perspectives and new directions for the production of bioethanol using consolidated bioprocessing of lignocellulose.

Publication Date: 2009 Jun 9 PMID: 19520566
Authors: Xu, Q. - Singh, A. - Himmel, M. E.
Journal: Curr Opin Biotechnol

The U.S. DOE Energy Independence and Security Act (EISA) mandated attainment of a national production level of 36 billion gallons of biofuels (to be added to gasoline) by 2022, of which 21 billion gallons must be derived from renewable/sustainable feedstocks (e.g. lignocellulose). In order to attain these goals, the development of cost effective process technologies that can convert plant biomass to fermentable sugars must occur. An alternative route to production of bioethanol is the utilization of microorganisms that can both convert biomass to fermentable sugars and ferment the resultant sugars to ethanol in a process known as consolidated bioprocessing (CBP). Although various economic benefits and technology hurdles must be weighed in the course of choosing the CBP strategy to be pursued, we present arguments for developing the powerfully cellulolytic fungus, Trichoderma reesei, as an effective CBP microorganism.

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Plant biomass degradation by gut microbiomes: more of the same or something new?

Publication Date: 2009 Jun 8 PMID: 19515552
Authors: Morrison, M. - Pope, P. B. - Denman, S. E. - McSweeney, C. S.
Journal: Curr Opin Biotechnol

Herbivores retain within their gastrointestinal tract a microbiome that specializes in the rapid hydrolysis and fermentation of lignocellulosic plant biomass. With the emergence of high-throughput DNA sequencing technologies and related 'omics' approaches, along with demands to better utilize lignocellulose materials as a feedstock for second-generation biofuels, these gut microbiomes are thought to be a potential source of novel biotechnologies relevant to meeting these needs. This review provides an insight into the new findings that have arisen from the (meta)genomic analysis of specialist cellulolytic bacteria and gut microbiomes of herbivorous insects, ruminants, native Australian marsupials, and other obligate herbivores. In addition to there being more of the same in terms of cellulases and cellulosomes, there also appears to be something 'new' in terms of the compositional and functional attributes of the plant cell wall deconstruction systems employed by these bacteria. However, future dissection and capture of useful biotechnologies via metagenomics will need more than the production of data using next generation sequencing technologies.

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New improvements for lignocellulosic ethanol.

Publication Date: 2009 Jun 5 PMID: 19502048
Authors: Margeot, A. - Hahn-Hagerdal, B. - Edlund, M. - Slade, R. - Monot, F.
Journal: Curr Opin Biotechnol

The use of lignocellulosic biomass for the production of biofuels will be unavoidable if liquid fossil fuels are to be replaced by renewable and sustainable alternatives. Ethanol accounts for the majority of biofuel use worldwide, and the prospect of its biological production from abundant lignocellulosic feedstocks is attractive. The recalcitrance of these raw materials still renders proposed processes complex and costly, but there are grounds for optimism. The application of new, engineered enzyme systems for cellulose hydrolysis, the construction of inhibitor-tolerant pentose-fermenting industrial yeast strains, combined with optimized process integration promise significant improvements. The opportunity to test these advances in pilot plants paves the way for large-scale units. This review summarizes recent progress in this field, including the validation at pilot scale, and the economic and environmental impacts of this production pathway.

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Enzymatic delignification of plant cell wall: from nature to mill.

Publication Date: 2009 Jun 5 PMID: 19502047
Authors: Martinez, A. T. - Ruiz-Duenas, F. J. - Martinez, M. J. - Del Rio, J. C. - Gutierrez, A.
Journal: Curr Opin Biotechnol

Lignin removal is a central issue in paper pulp manufacture, and production of other renewable chemicals, materials, and biofuels in future lignocellulose biorefineries. Biotechnology can contribute to more efficient and environmentally sound deconstruction of plant cell wall by providing tailor-made biocatalysts based on the oxidative enzymes responsible for lignin attack in Nature. With this purpose, the already-known ligninolytic oxidoreductases are being improved using (rational and random-based) protein engineering, and still unknown enzymes will be identified by the application of the different 'omics' technologies. Enzymatic delignification will be soon at the pulp mill (combined with pitch removal) and our understanding of the reactions produced will increase by using modern techniques for lignin analysis.

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Cellulases and biofuels.

Publication Date: 2009 Jun 5 PMID: 19502046
Authors: Wilson, D. B.
Journal: Curr Opin Biotechnol

There is a major international effort to develop renewable alternatives to fossil fuels. One approach is to produce a liquid fuel by enzymatically hydrolyzing carbohydrate polymers in biomass to sugars and fermenting them to ethanol. Cellulose is the main polymer in biomass and cellulases can hydrolyze it to cellobiose, which can be converted to glucose by beta-glucosidase. Extensive research is being carried out to try to obtain cellulases with higher activity on pretreated biomass substrates by screening and sequencing new organisms, engineering cellulases with improved properties and by identifying proteins that can stimutate cellulases. Despite extensive research on cellulases there are major gaps in our understanding of how they hydrolyze crystalline cellulose, act synergistically, and the role of carbohydrate binding modules.

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Closed photo-bioreactors as tools for biofuel production.

Publication Date: 2009 Jun 4 PMID: 19501503
Authors: Lehr, F. - Posten, C.
Journal: Curr Opin Biotechnol

Production of biofuels from microalgae is a promising sustainable option for the future. Unfortunately, until now production of algae biomass is too expensive owing to costly plant designs or high demand of auxiliary energy. These problems are addressed in recent developments. Basic ideas that are followed in different novel pilot plants are efficient mixing, high light dilution via large external surfaces or internal light conducting structures and gas transport via membranes. Other attempts are directed towards cheaper constructions. These endeavours have brought microalgal biofuel production closer to economic viability as has been shown in some pilot plants. But until now, these plants operate only on a small area and a limited time frame, making economic assessment difficult. The next years will show, whether these promises can be kept on a pure commercial basis for a whole process chain from algae cultivation to oil extraction during a whole year and on a real hectare.

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