Correction: Viruses' Life History: Towards a Mechanistic Basis of a Trade-Off between Survival and Reproduction among Phages

A comparison of life-history traits of 16 phages infecting E. coli reveals that although these viruses don't age, there is a trade-off between mortality and growth rate, which parallels that observed in many other species

Trade-Off between Bile Resistance and Nutritional Competence Drives Escherichia coli Diversification in the Mouse Gut

Bacterial diversification is often observed, but underlying mechanisms are difficult to disentangle and remain generally unknown. Moreover, controlled diversification experiments in ecologically relevant environments are lacking. We studied bacterial diversification in the mammalian gut, one of the most complex bacterial environments, where usually hundreds of species and thousands of bacterial strains stably coexist. Herein we show rapid genetic diversification of an Escherichia coli strain upon colonisation of previously germ-free mice. In addition to the previously described mutations in the EnvZ/OmpR operon, we describe the rapid and systematic selection of mutations in the flagellar flhDC operon and in malT, the transcriptional activator of the maltose regulon. Moreover, within each mouse, the three mutant types coexisted at different levels after one month of colonisation. By combining in vivo studies and determination of the fitness advantages of the selected mutations in controlled in vitro experiments, we provide evidence that the selective forces that drive E. coli diversification in the mouse gut are the presence of bile salts and competition for nutrients. Altogether our results indicate that a trade-off between stress resistance and nutritional competence generates sympatric diversification of the gut microbiota. These results illustrate how experimental evolution in natural environments enables identification of both the selective pressures that organisms face in their natural environment and the diversification mechanisms

Pertinences et impuissances d’une politique globale de changement autour des TICE face aux stratégies d’acteurs

Cet article présente le déploiement de l’Environnement Numérique de la Formation Initiale de Télécom Paris à la fois comme un élément inscrit de manière plus globale dans une politique de changement organisationnel menée par l’école, un instrument de ce changement et un objet socio-technique que les enseignants-chercheurs s’approprient. Par conséquent, si innovation pédagogique il y a, elle est moins liée à l’institutionnalisation du changement qu’aux initiatives locales et utilisations novatrices qui permettent d’appréhender un cours d’une manière différente.This paper presents the implementation of a web-based system for the academic programs at Telecom Paris, as a part of the policy of organizational change led by the school, an instrument of this change and a socio-technical object that the academic staff appropriates. As a result, if pedagogic innovation there is, it is less linked to the institutionalisation of change than to local initiatives and to the innovative uses which allow to teach in a different way

Dissecting the Genetic Components of Adaptation of Escherichia coli to the Mouse Gut

While pleiotropic adaptive mutations are thought to be central for evolution, little is known on the downstream molecular effects allowing adaptation to complex ecologically relevant environments. Here we show that Escherichia coli MG1655 adapts rapidly to the intestine of germ-free mice by single point mutations in EnvZ/OmpR two-component signal transduction system, which controls more than 100 genes. The selective advantage conferred by the mutations that modulate EnvZ/OmpR activities was the result of their independent and additive effects on flagellin expression and permeability. These results obtained in vivo thus suggest that global regulators may have evolved to coordinate activities that need to be fine-tuned simultaneously during adaptation to complex environments and that mutations in such regulators permit adjustment of the boundaries of physiological adaptation when switching between two very distinct environments

Pixelvetica. Sauvegarder le jeu vidéo suisse - État des lieux de la préservation du jeu vidéo en Suisse et dans le monde

Les jeux vidéo conservés dans les institutions de mémoire suisses font-ils partie de notre patrimoine audiovisuel ? Quelles mesures devraient être prises pour assurer leur conservation ? Ces questions et d’autres ont été examinées dans le cadre d’un projet pilote commandé par Memoriav, le pôle de compétence pour le patrimoine audiovisuel suisse, et réalisé par des partenaires issus du monde professionnel. Le rapport final est désormais disponible et sera présenté dans le cadre d’une manifestation en ligne le 25 janvier. Simultanément à son recensement du patrimoine audiovisuel suisse à l’échelle nationale, Memoriav a recueilli les premières conclusions de l’étude pilote « Pixelvetica » sur la situation de la conservation des jeux vidéo en Suisse. Cette étude s’avère pertinente pour Memoriav dans la mesure où, en Suisse, la production de jeux vidéo est encouragée par le biais du Message culture, mais les questions relatives à la conservation des œuvres ne sont pas encore résolues. Le projet initié par Memoriav et lancé au printemps 2021 a été mené par trois institutions spécialisées dans l’étude, la conservation et la médiation des œuvres numériques (GameLab UNIL-EPFL, Musée Bolo et Atelier 40a). Le rapport qui vient d’être publié s’appuie sur une enquête menée auprès de plus de 200 institutions suisses, ainsi que sur deux ateliers Memoriav organisés au printemps 2021 (en virtuel) et à l’automne (sur place), au cours desquels les résultats intermédiaires du projet ont été présentés et discutés. Une stratégie de politique culturelle est nécessaire Le rapport final présente un premier état des lieux significatif du rôle que jouent les jeux vidéo dans les institutions de mémoire suisses et montre que les jeux sont rarement considérés comme faisant partie du patrimoine culturel et audiovisuel. Le projet Pixelvetica a élaboré une série de recommandations stratégiques qui esquissent des pistes pour un traitement approprié des jeux vidéo dans les archives, les bibliothèques et les musées. Pour préserver à moyen terme le patrimoine culturel des jeux vidéo, une volonté politique culturelle forte et une stratégie concertée, soutenue par des instances compétentes, est nécessaire. Si l’étude souligne le retard de la Suisse dans la conservation de son patrimoine de jeux vidéo, en regard de ce qui a pu être constaté à travers les entretiens qui ont été menés à l’international, elle constate également qu’il existe de nombreux acteurs compétents en Suisse dans ce domaine, qui pourraient contribuer de manière décisive au développement d’une stratégie de conservation et d’étude du patrimoine des jeux vidéo en Suisse

Emergence of Variability in Isogenic Escherichia coli Populations Infected by a Filamentous Virus

The spread of epidemics not only depends on the average number of parasites produced per host, but also on the existence of highly infectious individuals. It is widely accepted that infectiousness depends on genetic and environmental determinants. However, even in clonal populations of host and viruses growing in homogeneous conditions, high variability can exist. Here we show that Escherichia coli cells commonly display high differentials in viral burst size, and address the kinetics of emergence of such variability with the non-lytic filamentous virus M13. By single-cell imaging of a virally-encoded fluorescent reporter, we monitor the viral charge distribution in infected bacterial populations at different time following infection. A mathematical model assuming autocatalytic virus replication and inheritance of bacterial growth rates quantitatively reproduces the experimental distributions, demonstrating that deterministic amplification of small host inhomogeneities is a mechanism sufficient to explain large and highly skewed distributions. This mechanism of amplification is general and may occur whenever a parasite has an initial phase of exponential growth within its host. Moreover, it naturally reproduces the shift towards higher virulence when the host is experimenting poor conditions, as observed commonly in host-parasite systems

The Durability of Public Goods Changes the Dynamics and Nature of Social Dilemmas

An implicit assumption underpins basic models of the evolution of cooperation, mutualism and altruism: The benefits (or pay-offs) of cooperation and defection are defined by the current frequency or distribution of cooperators. In social dilemmas involving durable public goods (group resources that can persist in the environment–ubiquitous from microbes to humans) this assumption is violated. Here, we examine the consequences of relaxing this assumption, allowing pay-offs to depend on both current and past numbers of cooperators. We explicitly trace the dynamic of a public good created by cooperators, and define pay-offs in terms of the current public good. By raising the importance of cooperative history in determining the current fate of cooperators, durable public goods cause novel dynamics (e.g., transient increases in cooperation in Prisoner's Dilemmas, oscillations in Snowdrift Games, or shifts in invasion thresholds in Stag-hunt Games), while changes in durability can transform one game into another, by moving invasion thresholds for cooperation or conditions for coexistence with defectors. This enlarged view challenges our understanding of social cheats. For instance, groups of cooperators can do worse than groups of defectors, if they inherit fewer public goods, while a rise in defectors no longer entails a loss of social benefits, at least not in the present moment (as highlighted by concerns over environmental lags). Wherever durable public goods have yet to reach a steady state (for instance due to external perturbations), the history of cooperation will define the ongoing dynamics of cooperators

Length Sensing and Control in the Virgo Gravitational Wave Interferometer

The gravitational wave detector Virgo is presently being commissioned. A significant part of last year was spent in setting up the cavity length control system. This work was carried out with steps of increasing complexity: locking a simple Fabry-Perot cavity, then a Michelson interferometer with Fabry-Perot cavities in both arms, and finally recycling the light beam into the interferometer. The applied strategy and the main results obtained are describe

The Virgo interferometric gravitational antenna

Submitted to: Class. Quantum Grav.The interferometric gravitational wave detectors represent the ultimate evolution of the classical Michelson interferometer. In order to measure the signal produced by the passage of a gravitational wave, they aim to reach unprecedent sensitivities in measuring the relative displacements of the mirrors. One of them , the 3-km-long Virgo gravitational wave antenna, which will be particularly sensitive in the low frequency range (10-100 Hz), is presently in its commissioning phase. In this paper the various techniques developed in order to reach its target extreme performance are outlined