1,721,079 research outputs found
Recommended from our members
Mechanisms in bacterial utilization of cellular debris in the ocean
Full text linkThis dissertation investigates the mechanisms of bacterial utilization of cells and cellular debris in the ocean. Bacteria are key members of marine ecosystems. They serve as the predominant biotic force acting on marine biogeochemical cycling of organic matter, and exert a strong influence on marine microbial community dynamics via their cell-cell interactions. While scientists have begun to untangle the web of seemingly intractable mechanisms that marine bacteria use to acquire and consume organic matter, many unknowns still remain.This research implements a number of techniques including bacterial production measurements, mass spectrometry, single-cell analyses, and genetics to test two hypotheses: (1) that bacteria can readily respond to a natural pulse of cellular debris from coral mass-spawning, and (2) that contact-dependent predatory bacteria can kill and consume their bacterial prey. Studies conducted off coastal Panama found that coral gametes elevated the organic matter concentration of the surrounding seawater by ~5-fold after a mass spawning event. Bacterial production measurements and 454 pyrosequencing of bromodeoxyuridine-labeled 16S bacterial rRNA genes showed that it was primarily active Rhodobacteraceae, Flavobacteriaceae, and Saprospiraceae taxa that degraded the coral gametes. High resolution mass spectrometry analysis supported this hypothesis, showing trends that indicated microbial alteration of the organic matter pool. This study demonstrated that coastal marine bacteria can readily respond to a large input of autochthonous cellular debris.Contact-dependent bacterial predation was tested by using bacteria with a type 6 secretion system (T6SS+) as model predators in competition assays. Nanoscale secondary ion mass spectrometry analysis showed that T6SS+ Vibrio cholerae utilized carbon from its bacterial prey. V. cholerae also exhibited the ability to utilize DNA and ribosomes from lysed bacteria as nutrients. Additionally, independent competition assays between T6SS+ V. cholerae and 15 different marine bacterial isolates showed that V. cholerae and/or the challenged isolate were killed in 12 out of the 15 assays. The experiments also revealed that the coral and shellfish pathogen, Vibrio coralliilyticus has a functional T6SS. Collectively, these results demonstrate that bacterial antagonism often ends in carnage for one or both of the competing species, and suggest that the susceptible prey are fresh fodder for the victorious bacterium
Recommended from our members
Bacterial surface-particle interactions: organic colloidal particle attachment and aggregation on cells
Full text linkMarine bacterial influence on colloidal dissolved organic matter is a major driver in the biogeochemical cycling of carbon through the marine microbial loop. Interactions of individual bacteria with ambient colloids can affect nutrient availability and acquisition strategies, reshaping their immediate microenvironment. Direct observation of marine bacteria using atomic force microscopy (AFM) and complementary microscopies can yield insight and empirical evidence regarding mechanisms and effects of interactions of individual bacterial with colloidal particles from dissolved organic matter. The discovery of bacterial nanotubes in marine bacteria is reported with descriptive physical properties. Nanotube structures in Pseudoalteromonas sp. TW7 cells and Alteromonas sp. ALTSIO cell were determined to range between 200–600 nm in length and 50–160 nm in width. Individual connections were observed as hollow structures connecting bacterial cytoplasmic spaces. Particle aggregates, ranging 40–200 nm in width, were localized on marine bacteria surfaces, varying in size and quantity in a cell population, from interactions with E. coli ribosomes as model colloids. TW7 cells were observed with altered surface corrugation features and surface pits that can influence surface interaction with individual colloids. Corrugation features were determined to be 50–100 nm in size, and 20 nm deep. Hollow surface pits were measured to be 50–300 nm in width, and 10–50 nm in depth. A method using curvature radius analysis is proposed for analyzing AFM time-lapse image data of ALTSIO exposed to E. coli ribosomes to quantify particle attachment rates and coverage of cells. From observations, bacteria presented an average increase of 6.0 attached ribosomes when exposed to ribosome-amended seawater medium (approximate concentration of 8×1011 particles mL-1). In conclusion, bacterial nanotubes, surface particle clusters and surface pits are various cell features in bacterial interactions with organic colloid particles that are indicative of underlying mechanisms of bacterial transformation of dissolved organic matter throughout the global ocean
Listening to Ice
No full textIs a feature-length film documenting sonic methods for understanding climate change from techno-scientific to socio-cultural. Through a number of site-based activities carried out at Drang Drung Glacier in the Zanskar region of the Himalayas team members set out to measure, monitor, and record the material transformations of the glacier as well as engage with local mountain communities directly impacted by climate change. Scientific activities included the deployment of an underwater sensor (hydrophone) at the glacial lake whereas workshops brought local villagers from Akshow to the glacier for sessions in “deep listening.” Lowering various hydrophones into its icy crevasses allowed us to tune into its subglacial streams, to hear the rushing of meltwater, and the underwater crackling of ice and popping air bubbles. For some, the glacier conjured the domesticated sound of boiling tea, for others the whir of a passing helicopter. In Leh, we met with local song collector Morup Namgyal who has been archiving folks songs about glaciers, mountains, rivers, and streams since the 1960s
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
HEAR: Himalayan Experiments in Acoustic Research
No full textH.E.A.R. is focused on “listening to glaciers and mountain communities” in the Himalayas. Through a number of site-based activities carried out at Drang Drung Glacier in the Zanskar region during September-October 2021, the project and its team members set out to measure, monitor, and record the material transformations of the glacier as well as engage with local mountain communities directly impacted by climate change and glacial recession. Alongside standard geophysical measurements, the research also sought to develop experimental methodologies for understanding climate change, in particular the use of acoustics sensing.
Scientific activities included the deployment of an underwater sensor (hydrophone) at the glacial lake, setting up both a GPS and meteorological weather station, as well as installing a series of bamboo stakes along a 15 km stretch into the ablation area of the glacier to measure annual changes in its mass balance.
Workshops brought local villagers to the glacier for sessions in “deep listening.” Lowering various hydrophones into its icy crevasses allowed us to tune into its subglacial streams, to hear the rushing of meltwater, and the underwater crackling of ice and popping air bubbles. For some, the glacier conjured the domesticated sound of boiling tea, for others the whir of a passing helicopter.
Realised by artist-researcher Susan Schuppli glaciologist Mohd. Farooq Azam, and community organiser Faiza Ahmad Khan Supported by a British Council COP26 Creative Commission, 202
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
- …
