1,721,080 research outputs found
Expression of CYP153A6 in acetic acid bacteria allowed the production of carboxylic acids starting from alkanes
No full textEnzymatic hydroxylation mediated by cytochrome P450 monooxygenases has been extensively studied since only molecular oxygen and reducing equivalents from NAD(P)H are requested for the reaction, which often occurs with high chemo- and regioselectivity. Even if many genetic approaches have been developed for the functional expression of CYP450 (together with cofactor regeneration systems and alkane transporter1), low biocatalytic efficiency and low enzymatic stability were frequently reported. Here we present the development of genetically modified acetic acid bacteria (AAB) as biocatalysts for the functionalization of methyl groups in the allylic position of different terpene derivatives (e.g., limonene, carveol, carvone) and non-functionalized methyl groups of aromatic substrates (e.g., toluene, xylenes, p-cymene, p-ethyl toluene).
We engineered two acetic acid bacteria (AAB) strains (Acetobacter malorum and Komagataeibacter xylinus) with a plasmid (based on the pSEVA331Bb vector backbone) encoding for a limonene monoxygenase operon from Mycobacterium spp. 1, including genes for the expression of a CYP153A6, a ferredoxin and a ferredoxin reductase for cofactor recycling.
The resulting recombinant strains were able to hydroxylate different terpenes thanks to the monooxygenase activity and to further oxidize alcohols into the corresponding aldehydes and carboxylic acids, exploiting the action of the AAB’s unspecific membrane-bound alcohols (ADH) and aldehydes (ALDH) dehydrogenases2. Their activity towards (S)- and (R)-limonene was compared with a recombinant strain of E. coli expressing the same genes2: whereas the use of the E. coli strain allowed for the preparation of perillyl alcohol, recombinant AABs gave complete oxidation of both the enantiomers of limonene to perillic acid, with transient formation of perillyl alcohol and perillaldehyde
REACTING THE ATOPIC WAY
No full textAtopy results from pathogenic mechanisms which are now known to a significant extent, also at the molecular level. This knowledge has been prompted by genetic studies showing that total IgE levels are genetically controlled and that synthesis of IgE directed against selected allergens is associated to particular HLA alleles. Atopic patients predominantly produce certain cytokines (especially IL-4) which indeed favour the synthesis of IgE, rather than other cytokines (IFN-gamma) which antagonize IgE production. Degranulation of mast cells and basophils is facilitated in atopic subjects because IgE receptors are more represented on the membrane of mastocytes, basophils (and other cells) of atopic than of non-atopic subjects. Furthermore a greater production of mediators with activity of > (HRF) carachterizes atopic patients. The genetically controlled production of certain cytokines which particularly stimulate eosinophils on one hand and the histaminic risk on the other, are further elements which underlie >: in other words, the particular predisposition towards developing atopic manifestations on the part of subjects whose > is characterized by this combination of factors
Acetic Acid Bacteria (AAB) as versatile whole-cell biocatalysts for intensified bioprocesses
Full text linkAcetic acid bacteria (AAB) are aerobic, Gram-negative microorganisms able to oxidise a wide variety of sugars, alcohols, and polyols with outstanding stereo- and regio- specificity, thanks to the action of their membrane and periplasmic space located dehydrogenases.
Our research group kept an all-round view on the synthetic potentialities of such biocatalyst, particularly focusing on their oxidative metabolism and on the widening of the obtainable molecules through genetic engineering approaches. We observed good conversion in the oxidation of aliphatic, aryl-aliphatic and benzyl alcohols to their corresponding acids. The transient aldehydic intermediate have been collected using a two-liquid phase extraction or by their conversion into oximes, further enlarging the possible achievable products. By the heterologous expression of a terminal monooxygenase, unfunctionalized hydrocarbons can be used by these bacteria as starting material; as a proof of concept, the conversion of limonene into perillartine (a natural sweetener) was studied.
AAB are particularly suitable for intensification processes since they can be immobilised in alginate beads and used in packed bed reactors to increase the STY, thus allowing to obtain high value products in a continuous-flow mode.
Moreover, we studied several strains able to grow on various agri-food waste and produce high quantity of bacterial cellulose, which has been further employed, once chemically functionalised, as efficient immobilisation support for esterases and glycosidases, retaining good residual activity
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
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