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Reversible adhesion by type IV pili leads to formation of irreversible localized clusters
No full textInternational audienceABSTRACT Despite the fact a fundamental first step in the physiopathology of many disease-causing bacteria is the formation of long-lived, localized, multicellular clusters, the spatio-temporal dynamics of the cluster formation process, particularly on host tissues, remains poorly understood. Experiments on abiotic surfaces suggest that the colonization of a surface by swimming bacteria requires i) irreversible adhesion to the surface, ii) cell proliferation, and iii) a phenotypic transition from an initial planktonic state. Here, we investigate how Pseudomonas aeruginosa (PA) infects a polarized MDCK epithelium and show that contrary to what has been reported on the colonization of abiotic surfaces, PA forms irreversible bacterial clusters on apoptotic epithelial cell without requiring irreversible adhesion, cell proliferation, or a phenotypic transition. By combining experiments and a mathematical model, we reveal that the cluster formation process is regulated by type IV pili (T4P). Furthermore, we unveil how T4P quantitatively operate during adhesion on the biotic surface, finding that it is a stochastic process that involves an activation time, requires the retraction of pili, and results in reversible adhesion with a characteristic attachment time. Using a simple kinetic model, we explain how such reversible adhesion process leads to the formation of irreversible bacterial clusters and quantify the cluster growth dynamics
Coordination of two opposite flagella allows high-speed swimming and active turning of individual zoospores
No full textInternational audiencePhytophthora species cause diseases in a large variety of plants and represent a serious agricultural threat, leading, every year, to multibillion dollar losses. Infection occurs when these biflagellated zoospores move across the soil at their characteristic high speed and reach the roots of a host plant. Despite the relevance of zoospore spreading in the epidemics of plant diseases, characteristics of individual swimming of zoospores have not been fully investigated. It remains unknown about the characteristics of two opposite beating flagella during translation and turning, and the roles of each flagellum on zoospore swimming. Here, combining experiments and modeling, we show how these two flagella contribute to generate thrust when beating together, and identify the mastigonemes-attached anterior flagellum as the main source of thrust. Furthermore, we find that turning involves a complex active process, in which the posterior flagellum temporarily stops, while the anterior flagellum keeps on beating and changes its gait from sinusoidal waves to power and recovery strokes, similar to Chlamydomonas's breaststroke, to reorient its body to a new direction. Our study is a fundamental step towards a better understanding of the spreading of plant pathogens' motile forms, and shows that the motility pattern of these biflagellated zoospores represents a distinct eukaryotic version of the celebrated 'run-and-tumble' motility class exhibited by peritrichous bacteria
Fast Decoding of the First Steps of Protein Aggregation Using a Nanopipette
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Modeling in Education: New Perspectives Opened by the Theory of Mathematical Working Spaces
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L’importation du MaaS (mobility as a service) en France : un nouvel instrument pour les politiques de transport ?
No full textInternational audienceThis article studies MaaS (Mobility as a Service) in France as an instrument of transport policies. Between the importation of the concept born in Finland and a heritage of pre-existing devices in France, this article attempts to understand the nature and challenges of a "French way" for the development of MaaS. Although it benefits from the support of public policies, MaaS is still struggling to find its way among the scales of transport organizing authorities. This work questions the reproduction of the silos of public policy while MaaS carries the promise of multimodal mobility, more fluid and intuitive despite the diversity of operators.Cet article étudie le MaaS (Mobility as a Service) en France en tant qu’instrument des politiques de transport. Entre l’importation du concept né en Finlande et l’héritage de dispositifs préexistants en France, cet article tente de comprendre la nature et les enjeux d’une « voie à la française » pour le développement du MaaS. Bien qu’il bénéficie d’un appui des politiques publiques, la mobilité servicielle peine encore à trouver sa voie parmi les échelles des autorités organisatrices de transport. Ce travail s’interroge sur la reproduction des cloisonnements de l’action publique alors que le MaaS porte la promesse d’une mobilité multimodale, plus fluide et intuitive malgré la diversité des opérateurs
Chaoticity in the vicinity of complex unstable periodic orbits in galactic type potentials
No full textInternational audienceWe investigate the evolution of phase space close to complex unstable periodic orbits in two galactic type potentials. They represent characteristic morphological types of disc galaxies, namely barred and normal (non-barred) spiral galaxies. These potentials are known for providing building blocks to support observed features such as the peanut, or X-shaped bulge, in the former case and the spiral arms in the latter. We investigate the possibility that these structures are reinforced, apart by regular orbits, also by orbits in the vicinity of complex unstable periodic orbits. We examine the evolution of the phase space structure in the immediate neighbourhood of the periodic orbits in cases where the stability of a family presents a successive transition from stability to complex instability and then to stability again, as energy increases. We find that we have a gradual reshaping of invariant structures close to the transition points and we trace this evolution in both models. We conclude that for time scales significant for the dynamics of galaxies, there are weakly chaotic orbits associated with complex unstable periodic orbits, which should be considered as structure-supporting, since they reinforce the morphological features we study
Snowmass2021 CMB-HD White Paper
No full textInternational audienceCMB-HD is a proposed millimeter-wave survey over half the sky that would be ultra-deep (0.5 uK-arcmin) and have unprecedented resolution (15 arcseconds at 150 GHz). Such a survey would answer many outstanding questions about the fundamental physics of the Universe. Major advances would be 1.) the use of gravitational lensing of the primordial microwave background to map the distribution of matter on small scales (k~10 h Mpc^(-1)), which probes dark matter particle properties. It will also allow 2.) measurements of the thermal and kinetic Sunyaev-Zel'dovich effects on small scales to map the gas density and velocity, another probe of cosmic structure. In addition, CMB-HD would allow us to cross critical thresholds: 3.) ruling out or detecting any new, light (< 0.1 eV) particles that were in thermal equilibrium with known particles in the early Universe, 4.) testing a wide class of multi-field models that could explain an epoch of inflation in the early Universe, and 5.) ruling out or detecting inflationary magnetic fields. CMB-HD would also provide world-leading constraints on 6.) axion-like particles, 7.) cosmic birefringence, 8.) the sum of the neutrino masses, and 9.) the dark energy equation of state. The CMB-HD survey would be delivered in 7.5 years of observing 20,000 square degrees of sky, using two new 30-meter-class off-axis crossed Dragone telescopes to be located at Cerro Toco in the Atacama Desert. Each telescope would field 800,000 detectors (200,000 pixels), for a total of 1.6 million detectors