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Non-conventional yeast-based platform to obtain value-added bioproducts
No full textYarrowia lipolytica è un lievito oleaginoso e non convenzionale con un significativo potenziale come fabbrica microbica biotecnologicamente rilevante. È versatile ed efficiente nell'utilizzare vari substrati, dai carboidrati come glucosio e glicerolo ai substrati idrofobici come acidi grassi, oli e acidi grassi volatili a catena corta. Questo lievito produce naturalmente una vasta gamma di prodotti, tra cui acidi organici, zuccheri, lipidi ed enzimi, rendendolo un ospite adatto per la produzione eterologa grazie agli strumenti molecolari recenti per la manipolazione genetica. Il primo capitolo esplora l'uso degli oli di cottura esausti (WCO) come materia prima per la produzione di oli cellulari (SCO) e lipasi usando il ceppo selvatico di Y. lipolytica. Lo studio dimostra la capacità del lievito di utilizzare alte concentrazioni di WCO per produrre lipidi intracellulari e lipasi extracellulari, con l'attività delle lipasi valutata mediante metodi spettrofotometrici e l'analisi dei lipidi intracellulari effettuata con citometria a flusso. Sono stati testati diversi mezzi minimali e condizioni di pH, rivelando una correlazione tra la riduzione degli acidi grassi liberi nel mezzo di coltura e l'aumento di SCO e dell'attività delle lipasi.
Il secondo capitolo si concentra sulla produzione di acido isocitrico (ICA) attraverso strategie di ingegneria genetica e miglioramento dei bioprocessi. Le modifiche genetiche hanno comportato la cancellazione del trasportatore mitocondriale del citrato Ylyhm2 e la sovraespressione dei geni YlSfc1 e Cex1, incrementando significativamente la produzione di ICA. La sovraespressione di YlOAC1, che codifica per il trasportatore mitocondriale dell'ossalacetato, ha migliorato il flusso di carbonio verso il ciclo dell'acido tricarbossilico, aumentando ulteriormente l'efficienza della produzione di ICA. Il processo ottimizzato ha raggiunto una produzione record di ICA di 152,7 g/L con una selettività del 92%. Il terzo capitolo esamina la produzione di acido itaconico (IA) utilizzando le vie biosintetiche di Aspergillus terreus e Ustilago maydis in Y. lipolytica, combinata con la cancellazione dei geni Ylyhm2 e Cex1, ottenendo una produzione elevata di IA su glucosio (55,08 g/L) e glicerolo (37,71 g/L), enfatizzando l'importanza della regolazione dei flussi metabolici e dell'uso di condizioni di coltivazione semplici. Il quarto capitolo si concentra sulla conversione dell'acetato in acido itaconico (IA) utilizzando un ceppo geneticamente ingegnerizzato di Y. lipolytica. L'ottimizzazione della supplementazione di amminoacidi, dei livelli di pH e delle dimensioni dell'inoculo ha migliorato la produzione di IA. Il processo di scala in un bioreattore da 5 litri utilizzando una strategia batch e fed-batch ha dimostrato la fattibilità, raggiungendo una produzione finale di IA di 3,0 g/L e 13,7 g/L di biomassa. Nonostante rese inferiori rispetto agli studi batterici precedenti, Y. lipolytica mostra promesse per la produzione di IA da acetato. Questi studi evidenziano la robustezza e la versatilità di Y. lipolytica come fabbrica microbica per la produzione sostenibile di composti ad alto valore come ICA e IA, enfatizzando l'importanza dell'ingegneria genetica e dei bioprocessi ottimizzati per applicazioni industriali.Yarrowia lipolytica is an oleaginous, unconventional yeast with significant potential as a biotechnologically relevant microbial factory. It is versatile and efficient in utilizing various substrates, from carbohydrates like glucose and glycerol to hydrophobic substrates such as fatty acids, oils, and volatile short-chain fatty acids. This yeast naturally produces a wide range of products, including organic acids, sugars, lipids, and enzymes, making it a suitable host for heterologous production through recent molecular tools for genetic manipulation. The first chapter explores the use of Waste Cooking Oils (WCOs) as a feedstock for producing Single Cell Oils (SCOs) and lipases using wild-type Y. lipolytica. The study demonstrates the yeast ability to utilize high concentrations of WCOs to produce intracellular lipids and extracellular lipases, with lipase activity assessed by spectrophotometric methods and intracellular lipids analysed using flow cytometry. Various minimal media and pH conditions were tested, revealing a correlation between reduced free fatty acids in the culture medium and increased SCO and lipase activity. The second chapter focuses on producing isocitric acid (ICA) through genetic engineering and bioprocess improvement strategies. Genetic modifications involved deleting the citrate mitochondrial carrier Ylyhm2 and overexpressing the citrate mitochondrial carrier YlSfc1 and the citrate membrane export Cex1 genes, significantly increasing ICA production. Overexpression of YlOAC1, encoding for oxaloacetate mitochondrial carrier, improved carbon flux towards the tricarboxylic acid cycle, further enhancing ICA production efficiency. The optimized process achieved a record ICA production of 152.7 g/L with a selectivity of 92%. The third chapter examines itaconic acid (IA) production using biosynthetic pathways from Aspergillus terreus and Ustilago maydis in Y. lipolytica, combined with deletion of Ylyhm2 and Cex1 genes, resulting in high IA production on glucose (55.08 g/L) and glycerol (37.71 g/L), emphasizing the importance of regulating metabolite fluxes and using simple cultivation conditions. The fourth chapter focuses on converting acetate into itaconic acid (IA) using genetically engineered Y. lipolytica. Optimizing amino acid supplementation, pH levels, and inoculum size enhanced IA production. The scale-up process in a 5-L bioreactor using a batch and fed-batch strategy demonstrated feasibility, achieving a final IA titre of 3.0 g/L and 13.7 g/L of biomass. Despite lower yields compared to bacterial studies, Y. lipolytica shows promise for IA production from acetate
Systematic screening for the biocatalytic hydration of fatty acids from different oily substrates by Elizabethkingia meningoseptica oleate hydratase through a Design-of-experiments approach
Full text linkThe edible plant oils production is associated with the release of different types of by-products. The latter
represent cheap and available substrates to produce valuable compounds, such as flavours and fragrances,
biologically active compounds and bio-based polymers. Elizabethkingia meningoseptica Oleate hydratases
(Em_OhyA) can selectively catalyze the conversion of unsaturated fatty acids, specifically oleic acid, into hydroxy
fatty acids, which find different industrial applications. In this study, Design-of-experiment (DoE) strategy was
used to screen and identify conditions for reaching high yields in the reaction carried out by Escherichia coli
whole-cell carrying the recombinant enzyme Em_OhyA using Waste Cooking Oils (WCO)-derived free fatty acids
(FFA) as substrate. The identified reaction conditions for high oleic acid conversion were also tested on untreated
triglycerides-containing substrates, such as pomace oil, sunflower oil, olive oil and oil mill wastewater (OMW),
combining the triglyceride hydrolysis by the lipase from Candida rugosa and the E. coli whole-cell containing
Em_OhyA for the production of hydroxy fatty acids. When WCO, sunflower oil and OMW were used as substrate,
the one-pot bioconversion led to an increase of oleic acid conversion compared to the standard reaction. This
work highlights the efficiency of the DoE approach to screen and identify conditions for an enzymatic reaction
for the production of industrially-relevant products
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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