1,720,960 research outputs found
Reinterpreting quorum sensing as positional sensing in bacterial communication
No full textBackground and Aims
The phenomenon of bacterial cell-to-cell communication via n-acyl homoserine lactone molecules was examined in a simple series of direct microscopy tests aimed at verifying the postulates of the current quorum sensing working model.
Methods
Using a wild type strain of Rhizobium leguminosarum, we first devised a signal production system in which cell number, cell density and cell distance could be varied at leisure while maintaining the physiological status and preventing further cell divisions. The model was subsequently verified by epifluorescent microscopy in a tri-dimensional set up in LB agar, using an rfp-tagged AHL producing strain of Pseudomonas aeruginosa and a sensor Escherichia coli bearing a gfp-fused AHL reporter gene.
Results
Data obtained by measuring 697 individual cell-to-cell communication distances using the CMEIAS image analysis software showed that indeed quorum sensing can be reduced to an interaction involving as few as two individual cells, with a mean calling distance of 37.4 um and a maximum calling distance extended as far as 123.6 um. Direct microscopy showed that a single bacterium can produce sufficient signal in situ to activate a population of 180 bacterial cells.
Conclusions
The results indicate that quorum sensing does not comply with the paradigm of a mechanism simply depending on cell density. A novel concept of positionally-releated sensing, via mixing concentration gradients, is presented
Wild legume root nodules as a potential reservoir for human pathogenic bacteria.
No full textA previous finding by our group (Benhizia et al., 2004) shows that root nodules from wild legumes,
besides their natural rhizobium symbionts, can host and multiply bacteria belonging to species
pathogenic to humans. These include Enterobacter cloacae, Enterobacter kobei, Escherichia vulneris,
Leclercia adecarboxylata, Pantoea agglomerans. As these taxa were repeatedly found in nodules from
three plant species, differing by habitat ecophysiology, and harvested in independent natural sites which
are spaced apart up to 150 Km from each other, we believe that the phenomenon can be a general
feature and have potentially significant impacts for the epidemiology of bacteria of clinical interest. In the
sole Italian territory nearly four hundred species of wild leguminous plants are known, whose
microbiological interactions are largely unknown. These plants can nevertheless develop abundant root
nodules, which are optimal sites for bacterial multiplication. Wild legume distribution can span over a
series of habitats, ranging from urban-synanthropic, to agricultural, and to the majority of natural
habitats. In light of the above findings, yielding five Enterobacterial taxa of potential danger to humans
from the analysis of only three species of wild plants, one could envisage the biomass of wild legumes as
possible strategic niche for the survival and active multiplication of clinical pathogens in hosts alternative
to mammals
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
Shovel roots: a unique stress-avoiding developmental strategy of the legume plant Hedysarum coronarium L.
No full textHedysarum coronarium (sulla) is a legume native to the Mediterranean basin, known for its broad tolerance to various environmental stresses, and its ability to thrive without signs of chlorosis when growing in arid and alkaline soils up to pH 9.6. A unique but poorly known morphological feature of its root system is the production of "shovels", modified lateral roots that acquire a curved and flattened shape. A combined structural and functional analysis was undertaken to define the nature and role of the shovel roots using various microscopy techniques, histochemical stains, STEM - energy dispersive X-ray microanalysis, infrared spectroscopy, and plant cultivation in different conditions. We found that sulla displays remarkable unique rhizosphere-buffering properties at both ends of the pH scale, and that shovels act as efficient calcium-absorbing organs that accumulate this cation intracellularly as insoluble crystalline salts. Such bioaccumulation results in a localized depletion of CaCO(3) from the soil. As a consequence of this removal of the pivotal carbonate buffering system, the iron-solubilizing acidification activities of the roots can become effective. Further tests revealed that the factor triggering shovel development is exposure of roots to iron oxide. This signal, reporting at once both iron presence and alkalinity, assures the availability of iron nutrient reserves upon acidification of the local microenvironment surrounding the roots. These findings, besides casting light on a novel and unique botanical phenomenon, offer the potential to exploit sulla's model and genes for the improvement of other crops to sustain productivity in a scenario of climate warming and increasing desertification
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