1,721,003 research outputs found
Microbial Engineering for Aldehyde Synthesis
Full text linkAldehydes are a class of chemicals with many industrial uses. Several aldehydes are responsible for flavors and fragrances present in plants, but aldehydes are not known to accumulate in most natural microorganisms. In many cases, microbial production of aldehydes presents an attractive alternative to extraction from plants or chemical synthesis. During the past 2 decades, a variety of aldehyde biosynthetic enzymes have undergone detailed characterization. Although metabolic pathways that result in alcohol synthesis via aldehyde intermediates were long known, only recent investigations in model microbes such as Escherichia coli have succeeded in minimizing the rapid endogenous conversion of aldehydes into their corresponding alcohols. Such efforts have provided a foundation for microbial aldehyde synthesis and broader utilization of aldehydes as intermediates for other synthetically challenging biochemical classes. However, aldehyde toxicity imposes a practical limit on achievable aldehyde titers and remains an issue of academic and commercial interest. In this minireview, we summarize published efforts of microbial engineering for aldehyde synthesis, with an emphasis on de novo synthesis, engineered aldehyde accumulation in E. coli, and the challenge of aldehyde toxicity.MIT Synthetic Biology Engineering Research Center (Grant EEC-0540879)National Science Foundation (U.S.). Graduate Research Fellowshi
Microbial engineering for aldehyde synthesis
No full textThesis: Ph. D., Massachusetts Institute of Technology, Department of Chemical Engineering, 2015.Cataloged from PDF version of thesis.Includes bibliographical references (pages 140-151).Microbes have been engineered to produce many useful classes of chemicals from renewable carbon sources instead of from finite petroleum reserves. Aldehydes represent a class of chemicals that has been challenging to obtain using microbes given the rapid conversion of aldehydes into their corresponding alcohols that occurs naturally. Microbes are thought to have evolved numerous endogenous enzymes responsible for catalyzing these conversions in order to alleviate the negative effect of many aldehydes on cellular processes. In this thesis, we investigate several aspects of microbial aldehyde synthesis. Driven first by the hypothesis that targeted gene deletions could decrease endogenous aldehyde reduction in a model E. coli host strain, we demonstrate that benzaldehyde accumulation occurs upon deletion of a combination of genes encoding enzymes known to have benzaldehyde reductase activity in vitro. Using deletion subset studies and quantitative real-time PCR, we discover that deletion of many, but not all, of these genes is required to curtail endogenous reduction. We also show that the same engineered strain has a significantly decreased rate of reduction of other aromatic aldehydes. As an added benefit, cell growth rate is unaffected by these deletions. We demonstrate the utility of this strain for two applications: (i) conversion of glucose into vanillin, which is the most widely used flavoring additive; and, (ii) conversion of benzaldehyde and glucose into L-phenylacetylcarbinol, which is a chiral pharmaceutical intermediate. We next explore the ability to produce and retain non-aromatic aldehydes with the specific objective of studying the conversion of fatty aldehydes into gasoline-range alkanes. We find that a carboxylic acid reductase (Car) from Nocardia iowensis achieves biosynthesis of aldehydes from free fatty acid substrates ranging in carbon chain length from C4 to C10. The use of Car, the engineered host strain, and previously elucidated pathways to free fatty acids enables production of alkanes ranging from C3 to C9. Although alcohol byproduct formation significantly decreases, it does not significantly increase alkane titer because of poor aldehyde decarbonylase kinetics. Additional work presented in this thesis seeks to identify and surmount limitations in aldehyde biosynthesis in vitro and in E. coli de novo vanillin biosynthesis.by Aditya Mohan Kunjapur.Ph. D
Modular and selective biosynthesis of gasoline-range alkanes
No full textTypical renewable liquid fuel alternatives to gasoline are not entirely compatible with current infrastructure. We have engineered Escherichia coli to selectively produce alkanes found in gasoline (propane, butane, pentane, heptane, and nonane) from renewable substrates such as glucose or glycerol. Our modular pathway framework achieves carbon-chain extension by two different mechanisms. A fatty acid synthesis route is used to generate longer chains heptane and nonane, while a more energy efficient alternative, reverse-β-oxidation, is used for synthesis of propane, butane, and pentane. We demonstrate that both upstream (thiolase) and intermediate (thioesterase) reactions can act as control points for chain-length specificity. Specific free fatty acids are subsequently converted to alkanes using a broad-specificity carboxylic acid reductase and a cyanobacterial aldehyde decarbonylase (AD). The selectivity obtained by different module pairings provides a foundation for tuning alkane product distribution for desired fuel properties. Alternate ADs that have greater activity on shorter substrates improve observed alkane titer. However, even in an engineered host strain that significantly reduces endogenous conversion of aldehyde intermediates to alcohol byproducts, AD activity is observed to be limiting for all chain lengths. Given these insights, we discuss guiding principles for pathway selection and potential opportunities for pathway improvement.United States. Army Research Office (Institute for Collaborative Biotechnologies. Grant W911NF-09-0001)Shell Global Solutions (US) Inc.National Science Foundation (U.S.). Graduate Research Fellowship ProgramUnited States. Dept. of Energy. Office of Science Graduate Fellowship Progra
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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