Description: Author(s): A. Fuhrer, F. J. Rueß, N. Moll, A. Curioni, and D. Widmer At submonolayer coverage, Mn forms atomic wires on the Si(001) surface oriented perpendicular to the underlying Si dimer rows. While many other elements form symmetric dimer wires at room temperature, we show that Mn wires have an asymmetric appearance and pin the Si dimers nearby. We find that an a... [Phys. Rev. Lett. 109, 146102] Published Wed Oct 03, 2012

Description: We investigated the roles of the Vibrio cholerae high-molecular-weight bifunctional penicillin binding proteins, PBP1a and PBP1b, in the fitness of this enteric pathogen. Using a screen for synthetic lethality, we found that the V. cholerae PBP1a and PBP1b proteins, like their Escherichia coli homologues, are each essential in the absence of the other and in the absence of the other's putative activator, the outer membrane lipoproteins LpoA and LpoB, respectively. Comparative analyses of V. cholerae mutants suggest that PBP1a/LpoA of V. cholerae play a more prominent role in generating and/or maintaining the pathogen's cell wall than PBP1b/LpoB. V. cholerae lacking PBP1b or LpoB exhibited wild-type growth under all conditions tested. In contrast, V. cholerae lacking PBP1a or LpoA exhibited growth deficiencies in minimal medium, in the presence of deoxycholate and bile, and in competition assays with wild-type cells both in vitro and in the infant mouse small intestine. PBP1a pathway mutants are particularly impaired in stationary phase, which renders them sensitive to a product(s) present in supernatants from stationary-phase wild-type cells. The marked competitive defect of the PBP1a pathway mutants in vivo was largely absent when exponential-phase cells rather than stationary-phase cells were used to inoculate suckling mice. Thus, at least for V. cholerae PBP1a pathway mutants, the growth phase of the inoculum is a key modulator of infectivity.

Description: The population dynamics of Pseudocalanus elongatus have been investigated within the framework of the GLOBEC-Germany project to gain a better understanding of its life cycle and population dynamics and to estimate secondary production in the North Sea. During an intensive field study in the German Bight between February and October 2004, experiments on reproduction were performed and data on length of copepodids and abundance were collected to characterize the population in the southern North Sea. This data set was used to update the literature-based parameterization of a population model for P. elongatus to investigate the population dynamics, life history and production in the German Bight. The ability of data to improve population models is also discussed. Pseudocalanus elongatus was found to be a major contributor to carbon uptake contributing about one-third of copepod production. Though the spatial variability in field observations was not reflected by the model, the simulation matched data within one order of magnitude at most stations. The high-resolution field observations and experiments mainly improved the parameterization of the reproductive parameters. Mortality is found to be a critical parameter due to its influence on population size. Using constant rates, though based on observation-derived estimates, seems not to capture realistic variability. Our study confirms the need for experimental and field data to build a robust parameterization for concentration-based population models.

Description: Background.  Extensively drug-resistant tuberculosis (XDR-tuberculosis) is a global public health threat, but few data exist elucidating factors driving this epidemic. The initial XDR-tuberculosis report from South Africa suggested transmission is an important factor, but detailed epidemiologic and molecular analyses were not available for further characterization. Methods.  We performed a retrospective, observational study among XDR-tuberculosis patients to identify hospital-associated epidemiologic links. We used spoligotyping, IS 6110 -based restriction fragment–length polymorphism analysis, and sequencing of resistance-determining regions to identify clusters. Social network analysis was used to construct transmission networks among genotypically clustered patients. Results.  Among 148 XDR-tuberculosis patients, 98% were infected with human immunodeficiency virus (HIV), and 59% had smear-positive tuberculosis. Nearly all (93%) were hospitalized while infectious with XDR-tuberculosis (median duration, 15 days; interquartile range: 10–25 days). Genotyping identified a predominant cluster comprising 96% of isolates. Epidemiologic links were identified for 82% of patients; social network analysis demonstrated multiple generations of transmission across a highly interconnected network. Conclusions.  The XDR-tuberculosis epidemic in Tugela Ferry, South Africa, has been highly clonal. However, the epidemic is not the result of a point-source outbreak; rather, a high degree of interconnectedness allowed multiple generations of nosocomial transmission. Similar to the outbreaks of multidrug-resistant tuberculosis in the 1990s, poor infection control, delayed diagnosis, and a high HIV prevalence facilitated transmission. Important lessons from those outbreaks must be applied to stem further expansion of this epidemic.

Description: Background Retinoblastoma (Rb) is a childhood cancer of the retina, commonly initiated by biallelic inactivation of the RB1 gene. Knowledge of the presence of a heritable RB1 mutation can help in risk management and reproductive decision making. We report here on RB1 mutation scanning in a unique nationwide cohort of Rb patients from the Netherlands. Methods From the 1173 Rb patients registered in the Dutch National Retinoblastoma Register until January 2013, 529 patients from 433 unrelated families could be included. RB1 mutation scanning was performed with different detection methods, depending on the time period. Results Our mutation detection methods revealed RB1 mutations in 92% of bilateral and/or familial Rb patients and in 10% of non-familial unilateral cases. Overall an RB1 germline mutation was detected in 187 (43%) of 433 Rb families, including 33 novel mutations. The distribution of the type of mutation was 37% nonsense, 20% frameshift, 21% splice, 9% large indel, 5% missense, 7% chromosomal deletions and 1% promoter. Ten per cent of patients were mosaic for the RB1 mutation. Six three-generation families with incomplete penetrance RB1 mutations were found. We found evidence that two variants, previously described as pathogenic RB1 mutations, are likely to be neutral variants. Conclusions The frequency of the type of mutations in the RB1 gene in our unbiased national cohort is the same as the mutation spectrum described worldwide. Furthermore, our RB1 mutation detection regimen achieves a high scanning sensitivity.

Description: The cell poles constitute key subcellular domains that are often critical for motility, chemotaxis, and chromosome segregation in rod-shaped bacteria. However, in nearly all rods, the processes that underlie the formation, recognition, and perpetuation of the polar domains are largely unknown. Here, in Vibrio cholerae , we identified HubP (hub of the pole), a polar transmembrane protein conserved in all vibrios, that anchors three ParA-like ATPases to the cell poles and, through them, controls polar localization of the chromosome origin, the chemotactic machinery, and the flagellum. In the absence of HubP, oriCI is not targeted to the cell poles, chemotaxis is impaired, and a small but increased fraction of cells produces multiple, rather than single, flagella. Distinct cytoplasmic domains within HubP are required for polar targeting of the three ATPases, while a periplasmic portion of HubP is required for its localization. HubP partially relocalizes from the poles to the mid-cell prior to cell division, thereby enabling perpetuation of the polar domain in future daughter cells. Thus, a single polar hub is instrumental for establishing polar identity and organization.

Description: Shelves have been estimated to account for more than one-fifth of the global marine primary production. It has been also conjectured that shelves strongly influence the oceanic absorption of anthropogenic CO2 (carbon shelf pump). Owing to their coarse resolution, currently applied global climate models are inappropriate to investigate the impact of climate change on shelves and regional models do not account for the complex interaction with the adjacent open ocean. In this study, a global ocean general circulation model and biogeochemistry model were set up with a distorted grid providing a maximal resolution for the NW European shelf and the adjacent northeast Atlantic. Using model climate projections we found that already a~moderate warming of about 2.0 K of the sea surface is linked with a reduction by ~ 30% of the biological production on the NW European shelf. If we consider the decline of anthropogenic riverine eutrophication since the 1990s, the reduction of biological production amounts is even larger. The relative decline of NW European shelf productivity is twice as strong as the decline in the open ocean (~ 15%). The underlying mechanism is a spatially well confined stratification feedback along the continental shelf break. This feedback reduces the nutrient supply from the deep Atlantic to about 50%. In turn, the reduced productivity draws down CO2 absorption in the North Sea by ~ 34% at the end of the 21st century compared to the end of the 20th century implying a strong weakening of shelf carbon pumping. Sensitivity experiments with diagnostic tracers indicate that not more than 20% of the carbon absorbed in the North Sea contributes to the long-term carbon uptake of the world ocean. The rest remains within the ocean's mixed layer where it is exposed to the atmosphere. The predicted decline in biological productivity, and decrease of phytoplankton concentration (in the North Sea by averaged 25%) due to reduced nutrient imports from the deeper Atlantic will probably affect the local fish stock negatively and therefore fisheries in the North Sea.