Cryo-EM Structure of Functional BK Channels in Lipid Bilayers

It has already widely been shown that the extension of the urban space takes a polycentric shape: suburban employment sub-centres emerge. The objective in this study is to measure employment concentrations inside and around urban agglomerations and to determine operational tools (methods and data) that lead to the highlighting of these sub-centers. Advantages and limits of the methods are discussed. Our cases studies are Antwerp and Brussels. The results obtained by several methodologies are compared (shift and share analysis, cluster analysis, kernel interpolation and local autocorrelation) for three different types of employment data (social security, population census and regional development statistics) and at three different scales of analysis (individual postal address, neighbourhood and commune). The main difficulties encountered are: (1) the spatial and temporal heterogeneity of the data, and (2) the non-uniqueness of the methodology for discriminating sub-centers. Our conclusion is that there is an emerging polycentric structure in Brussels and Antwerp, but sub-centers are still difficult to put forward. The combination of several different methods and databases is necessary to get insight in the polycentric structure

Paleontology in France: 200 years in the footsteps of Cuvier and Lamarck

International audienceDue to its richness in fossil localities and Fossil-Lagerstätten, France played a major role in the 18th and 19th centuries in establishing paleontology and biostratigraphy as scientific disciplines. The French naturalist and zoologist Cuvier (1769-1832) established the fields of comparative anatomy and paleontology, and proposed the concept of 'catastrophism' in geology. The naturalist Lamarck (1744-1829) is considered the founder of invertebrate paleontology and biostratigraphy and an early pioneer in the studies of evolution, developing the idea of 'transformism' and creating the word 'fossil', while his successor Blainville (1777-1850) was the first to use the word 'paleontology'. Based on this rich heritage, numerous French scientists strengthened paleontology as an important discipline during the 19th and 20th centuries. Paleontology was present at the universities of most major French cities, as documented by the rich collections in over 50 natural history museums and university collections. The most significant paleontological collection is that housed in the Muséum National d'Histoire Naturelle (MNHN) at Paris that currently hosts the largest research unit in paleontology of France with over 100 scientists, curators and technicians. The second largest collection (and the largest in terms of invertebrate fossils) is housed at the University of Lyon1, where the most important university paleontology research team is present. About 250 professional paleontologists are currently working in research units that are mostly affiliated to the Centre National de Recherche Scientifique (CNRS), in public or private museums, or in the numerous natural parcs. A significant generation change took place in the early 2000s, with the retirement of the paleontologists recruited in the 1960s and 1970s, that were often specialized in alpha-taxonomy and stratigraphy, and the arrival of a young generation of scientists that attempts to answer more 'modern' questions, such as global (climate) change, biodiversity, or evolution. This new generation of paleontologists faces modified funding schemes with project-based supporting structures in a more and more competitive environment. In the present paper we attempt to summarize the current situation of paleontology as a discipline in the very complex academic and scientific context of France. After a short overview on the history of French paleontology in the last centuries, a synopsis on institutions and funding agencies is presented briefly. The major research departments and their research themes are then described, together with the most important collections, the paleontological associations, journals, and databases, etc. Paleontological training possibilities and job opportunities, in particular in academia, are next documented, concluding with a summary of the prospects of the discipline

Phytoplankton dynamics from the Cambrian Explosion to the onset of the Great Ordovician Biodiversification Event: a review of Cambrian acritarch diversity

Most early Palaeozoic acritarchs are thought to represent a part of the marine phytoplankton and so constituted a significant element at the base of the marine trophic chain during the ‘Cambrian Explosion’ and the subsequent ‘Great Ordovician Biodiversification Event.’ Cambrian acritarch occurrences have been recorded in a great number of studies. In this paper, published data on Cambrian acritarchs are assembled in order to reconstruct taxonomic diversity trends that can be compared with the biodiversity of marine invertebrates. We compile a database and calculate various diversity indices at global and regional (i.e. Gondwana or Baltica) scales. The stratigraphic bins applied are at the level of the ten Cambrian stages, or of fourteen commonly used biozones in a somewhat higher resolved scheme. Our results show marked differences between palaeogeographical regions. They also indicate limitations of the data and a potential sampling bias, as the taxonomic diversity indices of species are significantly correlated with the number of studies per stratigraphic bin. The total and normalized diversities of genera are not affected in the same way. The normalized genus diversity curves show a slow but irregular rise over the course of the Cambrian. These also are the least biased. A radiation of species and to a lesser extent of genera in the ‘lower’ Cambrian Series 2 appears to mirror the ‘Cambrian Explosion’ of metazoans. This radiation, not evident on Gondwana, is followed by a prominent low in species diversity in the upper Series 3 and lower Furongian. Highest diversities are reached globally, and on both Baltica and Gondwana, in the uppermost Cambrian Stage 10, more precisely in the Peltura trilobite Zone, preceding a substantial phase of acritarch species extinction below and at the Cambrian/Ordovician boundary. Nearly all the genera present in Stage 10 survived into the Ordovician. The forms that emerged during the Cambrian therefore became the foundation for the more rapid radiation of acritarchs during the ‘Great Ordovician Biodiversification Event’

The palaeobiogeographical spread of the acritarch Veryhachium in the Early and Middle Ordovician and its impact on biostratigraphical applications

The genus Veryhachium Deunff, 1954, is one of the most frequently documented acritarch genera, being recorded from the Early Ordovician to the Neogene. Detailed investigations show that Veryhachium species first appeared near the South Pole in the earliest part of the Tremadocian (Early Ordovician). The genus was present at high palaeolatitudes (generally>60° S) on the Gondwanan margin during the Tremadocian before spreading to lower palaeolatitudes on the Gondwanan margin and other palaeocontinents (Avalonia and Baltica) during the Floian. It became cosmopolitan in the Middle and Late Ordovician. Although useful for distinguishing Ordovician from Cambrian strata, the diachronous first appearance data of Veryhachium morphotypes mean that they should be used with caution for long-distance correlation

Insights into palaeobotany

Copyright © 2023 Société botanique de France. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. The attached file is the published version of the article

The Ordovician System: From overlapping unit stratotypes to Global Boundary Stratotype Sections and Points

For nearly a century the Ordovician System was hidden as Murchison and Sedgwick tussled over the overlapping ground between their Silurian and Cambrian systems. The Ordovician is, in fact, one of the longest of the geological periods, characterised by major magmatic and plate tectonic activity; the roles of microcontinents and volcanic archipelagos were significant in shaping the Ordovician planet and the evolution of its biotas, associated with an immense biodiversification, significant fluctuations in climate and sea levels, and the first Phanerozoic mass extinction of marine invertebrates. The period was unique in being thalassocratic; epicontinental seas had a wider reach than during any other geological period. The land areas were restricted to isolated microblocks of archipelagos of various sizes with low relief, with rivers traversing gentle gradients, carrying sparse terrigenous material seaward. It is an ancient world with few parallels elsewhere in the Phanerozoic, and little in common with Holocene ecosystems and environments. The Ordovician System was introduced by Charles Lapworth as a solution to the stratotypes of overlapping units loosely defined by Adam Sedgwick for the Cambrian and by Roderick Murchison for the Silurian. Following a period of intensive research into all the key regions of the globe, unit stratotypes in the type areas of England and Wales have been replaced by seven global stages and three series based on Global Boundary Stratotype Sections and Points, enhancing the definition of these chronostratigraphic units and facilitating global correlation. As a consequence, the biological and geological events during the period can be recognised, and the magnitude and significance of originations and extinctions understood. A global synthesis of successions in Europe (Geological Society, London, Special Publications, 532) and the rest of the world (Geological Society, London, Special Publications, 533) has emphasised the importance of a universal language for Ordovician chronostratigraphy and its dividends

Global palaeogeographical implication of acritarchs in the Upper Ordovician

The EarlyâMiddle Ordovician peri-Gondwana and Baltica acritarch provinces are easily recognizable, illustrating a clear provincialism of global phytoplankton. However, acritarch assemblages have been reported to become increasingly similar towards the Late Ordovician, revealing a general cosmopolitanism, although, based on more recent studies, their assemblages from Laurentia and Baltica are reported to be rather different from those from peri-Gondwana. In this decade, new acritarch assemblages reported from South America, the Baltic region, Iran and Siberia, as well as the new material from South China and Tarim, provide additional data that help to understand the palaeobiogeographical distribution and evolution of phytoplankton during the Late Ordovician in more detail. The binary dataset was compiled based on published information from about 120 localities in South China, the Middle East, North Africa, South America, India, Bohemia, Avalonia, Laurentia, Baltica, North China, Tarim and Siberia. This dataset was used for Cluster Analysis (CA), Nonmetric Multidimensional Scaling (NMDS), and Network Analysis (NA) to understand acritarch palaeogeography in the Late Ordovician. Re-evaluation of the global palaeobiogeographical distribution of acritarchs revealed their clear provincialism also during the Late Ordovician, particularly in the Katian. The Late Ordovician acritarch provinces were related to global climatic zones. The highly diverse acritarch assemblage normally existed around 30° in the Southern Hemisphere, which is similar to the latitudinal diversity gradient model proposed by Zacaï et al. (2021) for the Late Ordovician. The total diversity of acritarchs was highest and their palaeobiogeographical differentiation strongest in the Katian. The higher acritarch diversity recorded in this time interval may have resulted from their clearly developed provincialism. Acritarch diversity decreased rapidly at the end of the Ordovician, evidently due to the Late Ordovician Mass Extinction (LOME). The relative proportion of endemic taxa in the assemblages in different regions was very high during the main part of the Late Ordovician. However, as a consequence of the LOME, the relative proportion of cosmopolitan taxa increased in the Hirnantian and became higher than in the Sandbian and Katian. Acritarch assemblages from different plates (regions) reacted to the LOME differently and exhibited various diversity trends

Assessment of the effects of sulfate and nitrate on the temporal evolution of Klebsiella oxytoca and Staphylococcus aureus abundance under shaking conditions, in aquatic microcosm

Most chemicals in natural aquatic media can be assimilated by bacteria. The impact of various environmental conditions on this microbial process is not always clear. This study aimed at investigating changes in the abundance of Klebsiella oxytoca and Staphylococcus aureus under different shaking conditions, in aquatic microcosms containing nitrate and sulfate. Sodium chloride solution (8.5 g NaCl•L-1), and nitrate and sulfate solutions (0.005, 0.05, 0.5 and 5 g•L-1) containing bacteria were supplemented with tryptic peptone at a final concentration of 10 g•L-1. The solutions were incubated under shaking conditions (300, 350 and 400 rev•min-1). Bacteriological analyses were performed hourly over a 6-h period. During the first 3 h of incubation, results showed that the highest values of the apparent cell growth rates (CAGRs) with K2SO4 in pure cultures, at a shaking speed 400 rev•min-1, were 0.656 h-1 for S. aureus, and 0.364 h-1 for K. oxytoca. In mixed culture, the CAGR was 0.235 h-1 for S. aureus, and 0.388 h-1 for K. oxytoca, both recorded at 300 rev•min-1. With KNO3 in pure culture solutions, the CAGR was 0.353 h-1 for S. aureus at 300 rev•min-1, and 0.367 h-1 for K. oxytoca at 350 rev•min-1. In mixed culture it was 0.454 h-1 for S. aureus and 0.393 h-1 for K. oxytoca, both recorded at 350 rev•min-1. The highest value of the apparent cell inhibition rate (CAIR) for S. aureus was 0.520 h-1 in K2SO4 (5 g•L-1, 400 rev•min-1), and 0.115 h-1 in KNO3 (5 g•L-1, 300 rev•min-1). For K. oxytoca, it was 0.07 h-1 in K2SO4 in pure culture (0.05 g•L-1, 300 rev•min-1), and 0.044 h-1 in mixed culture (0.05 g•L-1, 350 rev•min-1). In KNO3 it was 0.239 h-1 in mixed culture (5 g•L-1, 300 rev•min-1). The growth and inhibition potentials of different microbial species were impacted by the chemical concentrations and the movement speeds.L’impact de diverses conditions environnementales sur l’assimilation bactérienne dans l’eau, des composés chimiques est peu connu. La présente étude a visé l’évaluation de la dynamique d’abondance de Klebsiella oxytoca et Staphylococcus aureus sous diverses conditions, en milieu aquatique microcosme contenant du sulfate ou nitrate. Des solutions du NaCl (8,5 g•L-1), sulfate et nitrate (0,005, 0,05, 0,5 et 5 g•L-1) contenant des cellules ont été enrichies à la peptone trypsique (concentration finale 10 g•L-1), puis incubées sous conditions dynamiques (300, 350 et 400 tr•min-1). Les analyses bactériologiques ont été effectuées pendant 6 h. Il ressort qu’au cours des trois premières heures d'incubation, le taux de croissance cellulaire apparent (TCCA) le plus élevé en culture pure, contenant du K2SO4, est de 0,656 h-1 pour S. aureus, et 0,364 h-1 pour K. oxytoca, enregistrés à 400 tr•min-1. En culture mixte, il est de 0,235 h-1 pour S. aureus, et 0,388 h-1 pour K. oxytoca, enregistrés à 300 tr•min-1. Avec du KNO3, en culture pure, le TCCA est de 0,353 h-1 pour S. aureus à 300 tr•min-1, et 0,367 h-1 à 350 tr•min-1 pour K. oxytoka. En culture mixte, il est de 0,454 h-1 pour S. aureus et 0,393 h-1 pour K. oxytoca, enregistrés à 350 tr•min-1. Le taux d’inhibition cellulaire apparent (TICA) le plus élevé de S. aureus est de 0,520 h-1 en présence du K2SO4 (5 g•L-1, 400 tr•min-1), et 0,115 h-1 en présence de KNO3 (5 g•L-1, 300 tr•min-1). Pour K. oxytoca, il est de 0,07 h-1 avec du K2SO4 en culture pure (0,05 g•L-1, 300 tr•min-1), et 0,044 h-1 en culture mixte (0,05 g•L-1, 350 tr•min-1). Avec du KNO3, il est de 0,239 h-1 en culture mixte (5 g•L-1, 300 tr•min-1). La croissance et l’inhibition des microorganismes sont affectées par les concentrations en sels et la vitesse de mouvements du milieu

<i>Virgatasporites</i> and <i>Attritasporites</i>: the oldest land plant derived spores, cryptospores or acritarchs?

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