Advancing theory in media exposure and effects requires contending with an increasing level of complexity and contingency. Building on established theoretical concerns and the research possibilities enabled by large social datasets, we propose a framework for mapping information exposure of digitally situated individuals. We argue that from the perspective of an individual's personal communication network, comparable processes of "curation" are undertaken by a variety of actors-not only conventional newsmakers but also individual media users, social contacts, advertisers, and computer algorithms. Detecting the competition, intersection, and overlap of these flows is crucial to understanding media exposure and effects today. Our approach reframes research questions in debates such as polarization, selective and incidental exposure, participation, and conceptual orientations for computational approaches.

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Communication aimed at promoting civic engagement may become problematic when citizen roles undergo historic changes. In the current era, younger generations are embracing more expressive styles of actualizing citizenship defined around peer content sharing and social media, in contrast to earlier models of dutiful citizenship based on one-way communication managed by authorities. An analysis of 90 youth Web sites operated by diverse civic and political organizations in the United States reveals uneven conceptions of citizenship and related civic skills, suggesting that many established organization are out of step with changing civic styles.

Antibiotic-resistant enterococci are major causes of hospitalacquired infections. The emergence of Enterococcus faecalis as a significant nosocomial pathogen is a consequence of its inherent resistance to certain antibiotics and of its ability to survive and proliferate in the intestinal tract. Genetic determinants of E. faecalis conferring these properties are largely unknown. Here we show that PrkC, a one-component signaling protein containing a eukaryotic-type Ser/Thr kinase domain, modulates inherent antimicrobial resistance and intestinal persistence of E. faecalis. An E. faecalis mutant lacking PrkC grows at a wild-type rate in the absence of antimicrobial stress but exhibits enhanced sensitivity to cell-envelope-active compounds, including antibiotics that target cell-wall biogenesis and bile detergents. Consistent with its bile sensitivity, the mutant was also impaired at persistence in the intestine of mice. Thus, PrkC regulates key physiological processes in E. faecalis associated with its success as a nosocomial pathogen. The predicted domain architecture of PrkC comprises a cytoplasmic kinase domain separated by a transmembrane segment from extracellular domains thought to bind uncross-linked peptidoglycan, suggesting that PrkC is a transmembrane receptor that monitors the integrity of the E. faecalis cell wall and mediates adaptive responses to maintain cell-wall integrity. Given its role in modulating traits of E. faecalis important for its ability to cause nosocomial infections, we suggest that the one-component signaling protein PrkC represents an attractive target for the development of novel therapies to prevent infections by antibioticresistant enterococci.cell-envelope stress ͉ one-component system ͉ signal transduction ͉ cephalosporin resistance ͉ bile resistance

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Enterococcus faecalis is a common Gram-positive commensal bacterium of the metazoan gastrointestinal tract capable of biofilm formation and an opportunistic pathogen of increasing clinical concern. Dogma has held that biofilms are slow-growing structures, often taking days to form mature microcolonies. Here we report that extracellular DNA (eDNA) is an integral structural component of early E. faecalis biofilms (≤4 h postinoculation). Combining cationic dye-based biofilm matrix stabilization techniques with correlative immuno-scanning electron microscopy (SEM) and fluorescent techniques, we demonstrate that—in early E. faecalis biofilms—eDNA localizes to previously undescribed intercellular filamentous structures, as well as to thick mats of extruded extracellular matrix material. Both of these results are consistent with previous reports that early biofilms are exquisitely sensitive to exogenous DNase treatment. High-resolution SEM demonstrates a punctate labeling pattern in both structures, suggesting the presence of an additional, non-DNA constituent. Notably, the previously described fratricidal or lytic mechanism reported as the source of eDNA in older (≥24 h) E. faecalis biofilms does not appear to be at work under these conditions; extensive visual examination by SEM revealed a striking lack of lysed cells, and bulk biochemical assays also support an absence of significant lysis at these early time points. In addition, some cells demonstrated eDNA labeling localized at the septum, suggesting the possibility of DNA secretion from metabolically active cells. Overall, these data are consistent with a model in which a subpopulation of viable E. faecalis cells secrete or extrude DNA into the extracellular matrix.

S U M M A R YThe microbial glycocalyx is composed of a variety of polyanionic exopolysaccharides and plays important roles in microbial attachment to different substrata and to other cells. Here we report the successful use of low-voltage scanning electron microscopy (LVSEM) to visualize the glycocalyx in two microbial models ( Klebsiella pneumoniae and Enterococcus faecalis biofilms) at high resolution, and also the dependence on fixation containing polycationic dyes for its visualization. Fixation in a paraformaldehyde-glutaraldehyde cocktail without cationic dyes was inadequate for visualizing the glycocalyx, whereas addition of various dyes (alcian blue, safranin, and ruthenium red) to the aldehyde cocktail appeared necessary for stabilization. The cationic dyes varied in size, shape, and charge density, and these factors appeared responsible for different phenotypic appearances of the glycocalyx with each dye. These results suggest that aldehyde fixation with cationic dyes for high-resolution LVSEM will be a useful tool for investigation of microbial biofilms as well as investigation of the extent and role of the glycocalyx in microbial attachment to surfaces.