1,721,216 research outputs found
Atomic force microscopy reveals microscale networks and possible symbioses among pelagic marine bacteria
No full textMarine Bacteria and Archaea ('bacteria') interact with upper ocean productivity to fundamentally influence its biogeochemical fate with consequences for ecosystems and global climate. Most bacteria-mediated carbon cycling is due to numerically dominant free-living bacteria, but their adaptive strategies to interact with primary productivity are not fully understood. Using atomic force microscopy (AFM), we made the surprising discovery that a substantial, and variable, fraction (on average 30 +/- 17.8% with a range of 0 to 55%) of 'free-living' bacteria in our samples from California coastal and open ocean environments were, in fact, intimately associated with other bacteria at nanometer to micrometer scales. Twenty-one to 43% of bacteria, including Synechococcus, were conjoint. Such close associations could indicate symbioses; however, they could also be antagonistic, parasitic, neutral, or accidental. Further, a substantial fraction (4 to 55%) of bacteria was connected by pili and gels into cell-cell pairs or occurred in networks of up to 20 cells. We frequently observed nanoparticles associated with the networks, raising the question of their identity and origin (e.g. scavenged from the seawater colloid pool by the networks or produced by the bacteria within the networks). The networks occasionally contained structures that morphologically resembled coccoliths or protist scales. These may impart ballast to sinking particles if the networks coalesce to form larger, sinking, particles. Our finding of abundant bacteria-bacteria associations and possible microenvironment structuring by pelagic bacteria offers a novel context for bacterial ecology and diversity and models of ocean productivity and elemental cycling
A new class of transparent organic particles in seawater visualized by a novel fluorescence approach
No full textA method for visualizing transparent material in seawater, described here, has led to the discovery of novel particles. The protocol is based on Alcian Blue and SYBR Gold staining of seawater samples on polycarbonate filters. While the particles detected by our method may have some overlap with previously described transparent exopolymer particles and Coomassie stained particles, these particles largely comprise a previously undetected class. We propose that the particles are detected because they cause spatially explicit inhibition of Alcian Blue quenching of SYBR Cold fluorescence of the filter. Samples collected from various locations (Ellen Browning Scripps Memorial Pier, California, the Palmer Peninsula, Antarctica, and Point Conception, California) revealed particles with abundances on the order of 10 and 10(5) 1(-1) and ranging in size from 10 to 10(5) mu m(2). The particles varied in the types of organisms attached, the internal structure and probable biological sources. Field observations and laboratory experimental manipulations suggest varied sources and mechanisms of formation. These particles are potential hot spots of organic matter, microbial diversify and interactions, and, depending on their size and sinking rates, serve as conduits for carbon export to the ocean's interior
Microbial structuring of marine ecosystems
No full textDespite the impressive advances that have been made in assessing the diversity of marine microorganisms, the mechanisms that underlie the participation of microorganisms in marine food webs and biogeochemical cycles are poorly understood. Here, we stress the need to examine the biochemical interactions of microorganisms with ocean systems at the nanometre to millimetre scale - a scale that is relevant to microbial activities. The local impact of microorganisms on biogeochemical cycles must then be scaled up to make useful predictions of how marine ecosystems in the whole ocean might respond to global change. This approach to microbial oceanography is not only helpful, but is in fact indispensable
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
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