Flow cytometry analysis of germinating Bacillus spores, using membrane potential dye

Germination of Bacillus anthracis spores is necessary for the transcription of plasmidic genes essential to the infection. Assessing germination potential is crucial to predict the risk associated with pathogenic Bacillus exposure. The aim of this study was to set up a viability assay based on membrane potential in order to predict the earliest germination event of spores. B. cereus and two strains of B. subtilis were used. The spores were isolated with a sodium bromide gradient. Approximately 107 spores were incubated at 37°C in tryptic soy broth (TSB). Aliquots were harvested at predetermined times and stained with 3,3'-dihexyloxacarbocyanine iodide [DiOC6(3)] or with bis-(1,3-dibutylbarbituric acid) trimethine oxonol [DiBAC4(3)]. Fluorescence characteristics were obtained using flow cytometry. The earliest detectable activation of membrane potential occurred after 15 min of incubation in TSB using DiOC6(3). Using DiBAC4(3), the earliest detectable signal was after 4 h of incubation. Control experiments using carbonyl cyanide m-chlorophenylhydrazone (CCCP)-treated spores did not show any change in the fluorescence intensity over time. Since no membrane potential and no germination were detected in CCCP-treated spores, the activation of membrane potential seems to be associated with germination. DiOC6(3) can be used as an early membrane potential indicator for spores. DiBAC4(3), by contrast, is not a early membrane potential marker

Suspension feeding in the enigmatic Ediacaran organism Tribrachidium demonstrates complexity of Neoproterozoic ecosystems

The first diverse and morphologically complex macroscopic communities appear in the late Ediacaran period, 575 to 541 million years ago (Ma). The enigmatic organisms that make up these communities are thought to have formed simple ecosystems characterized by a narrow range of feeding modes, with most restricted to the passive absorption of organic particles (osmotrophy). We test between competing feeding models for the iconic Ediacaran organism Tribrachidium heraldicum using computational fluid dynamics. We show that the external morphology of Tribrachidium passively directs water flow toward the apex of the organism and generates low-velocity eddies above apical “pits.” These patterns of fluid flow are inconsistent with osmotrophy and instead support the interpretation of Tribrachidium as a passive suspension feeder. This finding provides the oldest empirical evidence for suspension feeding at 555 to 550 Ma, ~10 million years before the Cambrian explosion, and demonstrates that Ediacaran organisms formed more complex ecosystems in the latest Precambrian, involving a larger number of ecological guilds, than currently appreciated.</p

Formation et évolution des sols sur matériaux calcaires dans le piémont appalachien, Québec

Les sols développés sur matériaux calcaires et qualifiés de résiduels à semi-résiduels par les pédologues occupent plus de 15 000 ha au Québec. Quatre profils ont été échantillonnés près de Plessisville, dans un milieu de dépôts glaciaires, pour étudier la formation et l'évolution de tels sols. Les dépôts meubles ne dépassent pas 1 mètre d'épaisseur. Les schistes sont absents du solum des profils modérément bien drainés, tandis que leur contenu augmente depuis la surface vers la profondeur dans le profil mal drainé. Des mesures de désagrégation des schistes dans l'eau et HCI dilué ont montré que la décomposition des schistes est favorisée par la dissolution du carbonate. L'instabilité des schistes dans l'eau semble pouvoir expliquer le caractère résiduel des dépôts meubles. Pour connaître leur origine, glaciaire ou résiduelle, il paraît nécessaire d'étudier la relation roche arène dans un dépôt profond. Dans les profils modérément bien drainés, il y a formation de complexes organométalliques de Fe et Al, mais peu de transformation des minéraux. Un podzol humo-ferrique orthique et un brunisol mélanique orthique ont été identifiés. Le sol imparfaitement drainé montre peu de différenciation à l'intérieur du profil et il a été classé comme un brunisol mélanique gleyifié. Le carbonate éliminé a été transporté latéralement et s'est accumulé sous forme de marne dans la dépression voisine. Un humisol terrique s'est développé à cet endroit.Soils developed on calcareous parent materials and identified as "residual or semi-residual" by soil surveyors, cover more than 15,000 ha in Québec. Four profiles were sampled near Plessisville, in a once glaciated area, in order to study soil formation. Loose parent material over the rock did not exceed one meter. Shale fragments were absent in the moderately well drained profiles whereas the content increased with depth in the poorly drained one. Disaggregation tests carried out in water and dilute HCI indicated that the shale decomposed more easily when carbonate was dissolved. Shale disaggregation could account for the residual character of the parent material, as proposed by several authors. However, to assign more definitely a glacial or residual origin to the parent material in this area, it would be necessary to investigate the rock-arenite transition in a deeper deposit. In the moderately well drained profiles, mineral alteration was moderate and organometallic complexes were translocated to the B horizons. One profile was classified as an orthic humo-ferric podzol and the second one as an orthic melanic brunisol. There was only very slight profile development in the poorly drained soil that was classified as a gleyed melanic brunisol. Carbonate dissolved in the profiles moved to an adjacent depression, where it accumulated as a marl deposit; here a terric humisol developed.Die Bôden, die sich auf kalkhaltigem Material entwickelt haben, und die von den Bodenforschern als Rùckstandsbôden bis Halbrùckstandsbôden bezeichnet werden, nehmen mehr als 15 000 ha in Québec ein. Bei Plessisville sind in einem Milieu eiszeitlicher Ablagerungen vier Profil-Proben entnommen worden, urn die Bildung und Entwicklung solcher Bôden zu studieren. Die lockeren Ablagerungen sind nicht mehr als ein Meter tief. Im Boden der ziemlich gut entwàsserten Profile befinden sich keine Schiefer, wohingegen der Schiefer-Anteil in den schlecht entwàsserten Profilen von der Oberflàche bis in die Tiefe zunimmt. In Wasser und verdunntem HCI durchgefuhrte Zerfall-Tests der Schiefer haben gezeigt, da|i der Zerfall der Schiefer durch die Auflôsung des Karbonats begûnstigt wird. Die Labilitât der Schiefer im Wasser scheint den Ruckstandscharakter der lockeren Ablagerungen zu erklaren. Um ihre eiszeitliche Oder residuale Herkunft zu kennen, scheint es notwendig, die Beziehung Felsen-Grus in einer tiefgelegenen Ablagerung zu studieren. In den màpig gut entwàsserten Profilen findet man Organimetall-Komplexe von Fe und Al, aber wenig Verwandlung der Minérale. Ein "orthic humo-ferric" Podsol und ein "orthic melanic brunisol" wurden identifiziert. Der schlecht entwàsserte Boden weist wenig Differenzierung im lnnern des Profils auf, und er wurde als em "gleyed melanic brunisol" eingeordnet. Das eliminierte Karbonat ist seitwârts transportiert worden und hat sich in Form von Mergel in der Nachbarsenke angesammelt. An dieser Stelle hat sich ein erdiger Humusboden entwickelt

Population et urbanisation au Québec et au Canada, XIXe et XXe siècles

La croissance urbaine rapide de la fin du XIXe siècle et du premier tiers du XXe a suscité nombre de travaux sur un large éventail de sujets, notamment en rapport avec les processus démographiques associés à l'urbanisation: formation et évolution des populations des villes, transition démographique, structure et composition des ménages, rôles des membres des familles, logement, etc... Au Québec en particulier, les études sur les populations urbaines apparaissent plus fragmentaires. Si des recherches récentes ou en cours contribuent à une meilleure compréhension de l'urbanisation des Canadiens français (sinon de la franco-canadianisation des villes québécoises), il reste encore largement place pour des études englobantes de la croissance rapide qu'ont connue les villes entre 1860 et 1930. Ainsi est née l'idée d'un atelier sur cet objet éminemment complexe et interdisciplinaire que sont les populations urbaines du passé. Il visait à proposer quelques jalons quant aux pistes de recherche à explorer sur le sujet: jalons liés aux questionnements et problématiques, jalons méthodologiques sur les façons de faire, notamment par l'exploitation des données tirées des grandes séries documentaires tels les recensements nominatifs. Ce livret regroupe les contributions de quatre des huit conférenciers invités à lancer les échanges sur l'un ou l'autre des sujets proposés aux participants. Leur contenu offre diverses pistes susceptibles d'aider à mieux comprendre à échelle fine ce phénomène fondamental qu'est l'urbanisation des populations contemporaines

De l'Abbittibbi-Témiskaming 4

Ouvrage contenant les études suivantes: Jean Laflamme, «Le Marquis de Vaudreuil et l'Abitibi-Témiscamingue. Première partie: 1718-1724». Marc Charron, «Présentation sommaire d'un colonisateur de l'Abitibi: Hector Authier». Benoît-Beaudry Gourd, «Les travailleurs miniers et l'implantation du syndicalisme dans les mines de l'Abitibi-Témiscamingue 1925-1950». Marcel Desharnais, «Vingt ans de colonisation sous le régime coopératif. Guyenne 1947-1967.» Isabelle Boucher, «Histoire d'une pionnière de Villebois». Francine Boucher, «La place des filles au Collège du Nord-Ouest». Jo Godefroid, Rôle de l'appartenance sociale du niveau socio-économique dans l'orientation, les résultats et les perceptions des étudiants du Collège du Nord-Ouest»

Гендерная парадигма в образовании: от теории к практике

Computational fluid dynamics (CFD) simulations of water flow were performed in COMSOL. A model of Parvancorina sagitta from Russia with relief increased by 15% was oriented at 0° to the current and was fixed to the lower surface of a half-cylinder. Three-dimensional, incompressible flow of water was simulated with a normal inflow velocity inlet at the upstream end of the half-cylinder and a zero-pressure outlet at the downstream end. Slip boundary conditions were assigned to the top and sides of the half-cylinder, and no-slip boundary conditions were assigned to the Parvancorina model and the lower surface of the half-cylinder. The domain was meshed using free tetrahedral elements and the shear stress transport turbulence model was used to solve the Reynolds-averaged Navier–Stokes equations. A stationary solver was used to compute the steady-state flow patterns. Simulations were performed with an inlet velocity of 0.1, 0.2, and 0.5 m/s

Initial cyclostratigraphy of the middle Nama Group (Schwarzrand Subgroup) in southern Namibia

The Ediacaran Period includes critical evolutionary trends of early complex life as well as climatic variations associated with ocean oxygenation, glaciations, and carbon cycling, which are still poorly understood in terms of astronomical climate forcing. The middle Nama Group in southern Namibia was deposited during the late Ediacaran in mainly shallow marine environments within a foreland basin and consists of hierarchically arranged depositional sequences. Here, we test a possible astronomical origin of these sedimentary variations by developing an initial cyclostratigraphic framework based on satellite images integrated with recently published high-precision U-Pb zircon ages. Regular sedimentary alternations occur dominantly on scales of several tens of meters, accompanied by smaller- and larger-scale variations, and are correlatable over distances of ∼50 km. Throughout the studied succession, 35 to 39 alternations are recognized on this dominant scale, which have an average duration of ∼120–180 k.y. This duration corresponds well with the period of short eccentricity (∼100 k.y.), given the likely presence of hiatuses, or alternatively, the period of obliquity amplitude modulation (∼173 k.y.), which would imply no time is missing on this scale. The dominant alternations are consistent with previously identified medium-scale sequences in this succession, which have been interpreted to record fluctuations in relative or eustatic sea level. We hypothesize that astronomically-forced fluctuations in eustatic sea level modulated deposition of the middle Nama Group. Geochemical studies suggested a relation between fossil distribution, redox variability and sea level, implying that astronomical forcing may have played a role in the distribution of early complex life

Canopy Flow Analysis Reveals the Advantage of Size in the Oldest Communities of Multicellular Eukaryotes

SummaryAt Mistaken Point, Newfoundland, Canada, rangeomorph “fronds” dominate the earliest (579–565 million years ago) fossil communities of large (0.1 to 2 m height) multicellular benthic eukaryotes. They lived in low-flow environments, fueled by uptake [1–3] of dissolved reactants (osmotrophy). However, prokaryotes are effective osmotrophs, and the advantage of taller eukaryotic osmotrophs in this deep-water community context has not been addressed. We reconstructed flow-velocity profiles and vertical mixing using canopy flow models appropriate to the densities of the observed communities. Further modeling of processes at organismal surfaces documents increasing uptake with height in the community as a function of thinning of the diffusive boundary layer with increased velocity. The velocity profile, produced by canopy flow in the community, generates this advantage of upward growth. Alternative models of upward growth advantage based on redox/resource gradients fail, given the efficiency of vertical mixing. In benthic communities of osmotrophs of sufficient density, access to flow in low-flow settings provides an advantage to taller architecture, providing a selectional driver for communities of tall eukaryotes in contexts where phototropism cannot contribute to upward growth. These Ediacaran deep-sea fossils were preserved during the increasing oxygenation prior to the Cambrian radiation of animals and likely represent an important phase in the ecological and evolutionary transition to more complex eukaryotic forms.Video Abstrac