1,720,957 research outputs found
Systems Biotechnology: production of high-value added compounds from renewable resources
No full textL’accumulo delle plastiche monouso, ed in particolare del polietilene tereftalato (PET), è uno dei temi ambientali più importanti che la nostra società si trova ad affrontare. L’inerzia chimica e l’accumulo di questi materiali, anche sottoforma di microplastiche, nell’ambiente rappresenta uno dei maggiori problemi ambientali. La continua evoluzione delle biotecnologie, inclusa la scoperta di enzimi capaci di degradare il PET, offre strumenti innovativi per trasformare e valorizzare i rifiuti plastici di PET in prodotti chimici di alto valore, in un’ottica di bioeconomia circolare.
Questo progetto di dottorato mira ad ingegnerizzare un ceppo di E. coli attraverso la progettazione e l’inserimento di una cascata enzimatica artificiale progettata appositamente per utilizzare i prodotti derivati dalla degradazione enzimatica del PET. In particolare, l’obiettivo è la valorizzazione dell’acido tereftalico (TPA), uno dei monomeri rilasciati, convertendolo in piruvato, che è un intermedio chiave per la sintesi di composti di alto valore aggiunto come gli amminoacidi.
Il primo passo è stata l’ottimizzazione di ogni sezione della cascata enzimatica per individuare e risolvere eventuali passaggi limitanti, definendo allo stesso tempo un insieme di condizioni di reazione comuni e adatte a tutte le sezioni. Contemporaneamente è stata anche verificata la compatibilità di ogni sezione con l’approccio whole-cell.
Successivamente, tramite un approccio iterativo, si è arrivati alla definizione di un processo funzionale e ottimizzato per la produzione di piruvato direttamente dal TPA derivante dalla degradazione enzimatica del PET.
Lo scale-up del processo ha raggiunto una resa di processo del 77% in mgpiruvato/mgTPA (resa molare del 72%) e una resa complessiva del 34% in mgpiruvato/mgPET (resa molare del 41%) in condizioni di reazione moderate (30 °C). Questi risultati dimostrano l’alto potenziale economico dei rifiuti di PET e la concreta possibilità per la loro valorizzazione.The disposal of single-use plastics, particularly polyethylene terephthalate (PET), represents a major environmental issue due to its persistence and contribution to microplastic pollution. Advances in biotechnology, including the discovery of PET-hydrolyzing enzymes (PHEs), offer promising approaches to converting PET waste into valuable chemicals within the concept of circular bioeconomy.
The final goal of this PhD project was to engineer an E. coli strain capable of utilizing the products obtained from PET enzymatic degradation through a properly designed artificial enzymatic cascade. Specifically, the objective was to valorize the released monomer terephthalic acid (TPA) by converting it into pyruvate, a key intermediate for synthesizing high-value compounds such as amino acids.
Initially, each step of the proposed pathway was evaluated individually to overcome potential bottlenecks and to define a set of optimal and consistent reaction conditions for all sections. Furthermore, a step-by-step evaluation of the process’s compatibility with the whole-cell approach was carried out.
Subsequently, a series of optimization steps led to the development of a functional process for producing pyruvate directly from TPA derived from enzymatically degraded post-consumer PET waste.
Finally, the process was successfully scaled up, achieving a process yield of 77% in terms of mgpyruvate/mgTPA (i.e., 72% molar yield) and an overall yield of 34% in terms of mgpyruvate/mgPET (i.e., 41% molar yield) under mild conditions1. These results demonstrate the potential to valorize post-consumer PET waste and underscore this process’s relevance within pyruvate production technologies
Lignin Valorization: Production of High Value-Added Compounds by Engineered Microorganisms
Get PDFLignin is the second most abundant polymer in nature, which is also widely generated during biomass fractionation in lignocellulose biorefineries. At present, most of technical lignin is simply burnt for energy supply although it represents the richest natural source of aromatics, and thus it is a promising feedstock for generation of value-added compounds. Lignin is heterogeneous in composition and recalcitrant to degradation, with this substantially hampering its use. Notably, microbes have evolved particular enzymes and specialized metabolic pathways to degrade this polymer and metabolize its various aromatic components. In recent years, novel pathways have been designed allowing to establish engineered microbial cell factories able to efficiently funnel the lignin degradation products into few metabolic intermediates, representing suitable starting points for the synthesis of a variety of valuable molecules. This review focuses on recent success cases (at the laboratory/pilot scale) based on systems metabolic engineering studies aimed at generating value-added and specialty chemicals, with much emphasis on the production of cis,cis-muconic acid, a building block of recognized industrial value for the synthesis of plastic materials. The upgrade of this global waste stream promises a sustainable product portfolio, which will become an industrial reality when economic issues related to process scale up will be tackled
Valuable compounds from pollutants: converting PET into enantiopure alanine
Get PDFThe enzymatic depolymerization of single-use plastic products, primarily made from poly(ethylene terephthalate) (PET), is now a reality. Herein, we report the development of an innovative tandem system process that uses engineered enzymes and Escherichia coli strains to depolymerize PET and convert the resulting products into enantiomers of alanine, useful amino acids, and starting point for further valorization processes. A biosynthetic pathway has been generated, consisting of twelve enzymes derived from four different microorganisms. This pathway has been optimized using recombinant proteins and whole-cells that harbor different modules of the pathway. Specifically, the S101N/F243T-ΔLCC variant was selected to degrade PET into terephthalic acid (TPA) and ethylene glycol also at 37 °C, a temperature compatible with the E. coli RARE strain. A recombinant E. coli strain catalyzed the subsequent conversion of TPA into 2-pyrone-4,6-dicarboxylic acid, which is then transformed into pyruvate by recombinant enzymes to prevent depletion of pyruvate due to cellular catabolism. Finally, pyruvate is enzymatically aminated to enantiopure d- or l-alanine. We successfully converted postconsumer PET waste into d- and l-alanine, with an overall yield of 50 mg/170 mg PET, demonstrating that the bioconversion of selected plastics into valuable biomolecules via an eco-friendly process is feasible
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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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