1,720,969 research outputs found
Investigation of bacterial biosurfactant production for industrial use
No full textThis study presents part of a multifaceted study of microbial biosurfactants and their industrial potential. The first step was the assembly of a microbial culture collection of a variety of biosurfactant-producing organisms with the choice of biosurfactant types informed by the industrial partner. The choice was based on two main criteria, the ease of product recovery and its final yield. Two groups of glycolipid biosurfactants were selected for further study: rhamnolipids produced by Pseudomonas aeruginosa and sophorolipids by Candida spp. Efforts to manipulate the biosurfactant chemical profiles by changing the cultivation media (carbon source in particular) and conditions in shake-flasks, demonstrated that there is only a limited possibility for changing the biosurfactant composition. This raised the question of the extent to which biosurfactant production is constrained by genetic determinants? To overcome the limitations of the flask-scale production, selected P. aeruginosa and Candida strains were used in bioreactors, and rhamnolipids and sophorolipids were synthesised in quantities sufficient for extraction and purification. The purified biosurfactants were used by the project partners for further characterisation and formulation in trial industrial products. Rhamnolipid yields were approximately 10 g/L whilst sophorolipid production exceeded 100 g/L. Detailed examination of the orcinol assay, which is widely used for the determination of rhamnolipid yields, showed that the method is flawed and provides an overestimate of yield when compared to quantification following extraction and purification. The culture approach had demonstrated the restricted possibilities for manipulating rhamnolipid production profile in P. aeruginosa and therefore a wider range of strains from different environmental niches were selected for genetic analysis. The aim of this part of the investigation was to establish the extent of natural gene variation which could be exploited for customised biosurfactant production. The comparative analysis of the rhl genes, coding the factors involved in rhamnolipid biosynthesis, was carried out on different P. aeruginosa strains isolated from water, soil and including pathogenic strains infecting cystic fibrosis patients. The extent of the gene sequence diversity resulted < 5%, which indicated that the rhl genes are conserved and are part of the core genome of P. aeruginosa. The single polymorphisms that occurred on the gene sequences, which gave rise to several variants, revealed no clear effect on the phenotype but appeared rather random. These variants showed also no specific correlation with different habitats. The analysis of the codon usage further supported the confidence in the highly conservative nature of the rhl genes. Most amino acids were encoded by highly preferred codons, some of which were selected upon the optimal translational efficiency, some others were instead determined by the high GC content of P. aeruginosa genome. On the whole, our data correlated well in showing that rhamnolipid biosurfactants produced by P. aeruginosa are conserved in their structure and profile as well in the genetic makeup. As involved in many important biological activities under a variety of environmental conditions, rhamnolipids developed as highly fit molecules. In the light of this, it appears that the likelihood that isolates of P. aeruginosa displaying unusual rhamnolipid profiles and features occurring naturally would be limited. Alternative routes for the development of industrially customised rhamnolipid biosurfactants are suggested as either the genetic manipulation of P. aeruginosa or the screening of rhamnolipid-producing organisms closely related.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
Discovery and Characterization of a New Cold-Active Protease From an Extremophilic Bacterium via Comparative Genome Analysis and in vitro Expression
Get PDFFollowing a screening of Antarctic glacier forefield-bacteria for novel cold-active enzymes, a psychrophilic strain Psychrobacter sp. 94-6PB was selected for further characterization of enzymatic activities. The strain produced lipases and proteases in the temperature range of 4–18°C. The coding sequence of an extracellular serine-protease was then identified via comparative analysis across Psychrobacter sp. genomes, PCR-amplified in our strain 94-6PB and expressed in the heterologous host E. coli. The purified enzyme (80 kDa) resulted to be a cold-active alkaline protease, performing best at temperatures of 20–30°C and pH 7-9. It was stable in presence of common inhibitors [β-mercaptoethanol (β-ME), dithiothreitol (DTT), urea, phenylmethylsulfonyl fluoride (PMSF) and ethylenediaminetetraacetic acid (EDTA)] and compatible with detergents and surfactants (Tween 20, Tween 80, hydrogen peroxide and Triton X-100). Because of these properties, the P94-6PB protease may be suitable for use in a new generation of laundry products for cold washing. Furthermore, we assessed the microdiversity of this enzyme in Psychrobacter organisms from different cold habitats and found several gene clusters that correlated with specific ecological niches. We then discussed the role of habitat specialization in shaping the biodiversity of proteins and enzymes and anticipate far-reaching implications for the search of novel variants of biotechnological products
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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