9 research outputs found

    Rapid Pathway Evolution Facilitated by Horizontal Gene Transfers across Prokaryotic Lineages

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    The evolutionary history of biological pathways is of general interest, especially in this post-genomic era, because it may provide clues for understanding how complex systems encoded on genomes have been organized. To explain how pathways can evolve de novo, some noteworthy models have been proposed. However, direct reconstruction of pathway evolutionary history both on a genomic scale and at the depth of the tree of life has suffered from artificial effects in estimating the gene content of ancestral species. Recently, we developed an algorithm that effectively reconstructs gene-content evolution without these artificial effects, and we applied it to this problem. The carefully reconstructed history, which was based on the metabolic pathways of 160 prokaryotic species, confirmed that pathways have grown beyond the random acquisition of individual genes. Pathway acquisition took place quickly, probably eliminating the difficulty in holding genes during the course of the pathway evolution. This rapid evolution was due to massive horizontal gene transfers as gene groups, some of which were possibly operon transfers, which would convey existing pathways but not be able to generate novel pathways. To this end, we analyzed how these pathways originally appeared and found that the original acquisition of pathways occurred more contemporaneously than expected across different phylogenetic clades. As a possible model to explain this observation, we propose that novel pathway evolution may be facilitated by bidirectional horizontal gene transfers in prokaryotic communities. Such a model would complement existing pathway evolution models

    Old coins from the Medveščak brook in Zagreb

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    On July 28, 2005 a very unusual, didactic, extremely interesting and attractive exhibition called »A brook in the very heart of Zagreb. Following the Medveščak brook from its source to its mouth« was opened at the City of Zagreb Museum. Among the very many exhibits one could also see all coins and medals found there, preserved in the Zagreb Archaeological Museum Numismatic Cabinet (PREMERL 2005: 91, Nos. 1.37– 153). On November 17, 2005. at 7 PMthere was also the book launch of the exhibition catalogue, bearing the same title, written by Nada Premerl. Because a detailed coin catalogue could not be included in this valuable and interesting book, the authors wish to present it here. In 1899 during the construction of an underground canal to direct the water, workmen unearthed many objects, among them a considerable amount of old coins. A small part was rescued and the Zagreb Magistrate and Josip Pavlišić presented these coins to the Archaeological Museum. Josip Brunšmid, the Museum director in those days gave a detailed report and a list of the coins (BRUNŠMID 1900). Among the coins, found in the Medveščak, there were some Roman coins, which, together with other Roman coins found in Zagreb, have caused considerable interest since. After Brunšmid (1900) a few lines were dedicated to them by Josip Klemenc (1938: 104), and more recently by Z. Dukat (1994; 1996). Better preserved specimens of Roman coins were shown on the exhibition »Zagreb before Zagreb« (December 1994 – February 1995), also at the Zagreb City Museum (DUKAT 1994). The present catalogue, apart from the five Roman coins, includes the one mediaeval and 112 various modern coins. They have been processed by NUMIZ, a computer programme developed by the Numismatic Cabinet of the Slovenian National Museum in Ljubljana

    Formation mechanism of high-index faceted Pt-Bi alloy nanoparticles by evaporation-induced growth from metal salts

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    Abstract Nanoparticles with high-index facets are intriguing because such facets can lend the structure useful functionality, including enhanced catalytic performance and wide-ranging optical tunability. Ligand-free solid-state syntheses of high index-facet nanoparticles, through an alloying-dealloying process with foreign volatile metals, are attractive owing to their materials generality and high yields. However, the role of foreign atoms in stabilizing the high-index facets and the dynamic nature of the transformation including the coarsening and facet regulation process are still poorly understood. Herein, the transformation of Pt salts to spherical seeds and then to tetrahexahedra, is studied in situ via gas-cell transmission electron microscopy. The dynamic behaviors of the alloying and dealloying process, which involves the coarsening of nanoparticles and consequent facet regulation stage are captured in the real time with a nanoscale spatial resolution. Based on additional direct evidence obtained using atom probe tomography and density functional theory calculations, the underlying mechanisms of the alloying-dealloying process are uncovered, which will facilitate broader explorations of high-index facet nanoparticle synthesis
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