Magneto-Roton Modes of the Ultra Quantum Crystal: Numerical Study

The Field Induced Spin Density Wave phases observed in quasi-one-dimensional conductors of the Bechgaard salts family under magnetic field exhibit both Spin Density Wave order and a Quantized Hall Effect, which may exhibit sign reversals. The original nature of the condensed phases is evidenced by the collective mode spectrum. Besides the Goldstone modes, a quasi periodic structure of Magneto-Roton modes, predicted to exist for a monotonic sequence of Hall Quantum numbers, is confirmed, and a second mode is shown to exist within the single particle gap. We present numerical estimates of the Magneto-Roton mode energies in a generic case of the monotonic sequence. The mass anisotropy of the collective mode is calculated. We show how differently the MR spectrum evolves with magnetic field at low and high fields. The collective mode spectrum should have specific features, in the sign reversed "Ribault Phase", as compared to modes of the majority sign phases. We investigate numerically the collective mode in the Ribault Phase.Comment: this paper incorporates material contained in a previous cond-mat preprint cond-mat/9709210, but cannot be described as a replaced version, because it contains a significant amount of new material dealing with the instability line and with the topic of Ribault Phases. It contains 13 figures (.ps files

<em>Listeria monocytogenes</em>

Prod 2017-266 équipe EA UB BIOMENational audiencerésumé du livre : Pour garantir et maîtriser la sécurité microbiologique des aliments et prévenir les crises sanitaires alimentaires, la connaissance et la surveillance des microorganismes pathogènes depuis la production primaire jusqu’à la distribution des denrées alimentaires en passant par la transformation, sont indispensables. Cet ouvrage de référence traite des dangers microbiologiques alimentaires majeurs (microorganismes infectieux ou toxines d’origine microbienne) et des risques associés pour l’Homme. Illustré de nombreux schémas et tableaux de synthèse, il fait un point complet sur les notions fondamentales de microbiologie générale, de physiologie microbienne et de modélisation, en les appliquant aux microorganismes pathogènes des aliments et en y intégrant les dernières avancées. Il présente ensuite les outils de gestion du risque microbiologique mis en place au niveau européen et français. Enfin, les microorganismes avérés ou émergents d’intérêt font l’objet de monographies claires et détaillées permettant de bien les connaître pour mieux les maîtriser. Cet ouvrage s’adresse aux managers, ingénieurs et techniciens des industries agroalimentaires (des secteurs qualité-hygiène, production, achats, recherche et développement...), aux professionnels du contrôle sanitaire et de la gestion du risque (laboratoires d’analyses et instances officielles) ainsi qu’aux enseignants-chercheurs et aux étudiants dans le domaine de la microbiologie appliquée à l’agroalimentaire et des risques sanitaires

Ecology of <em>Listeria monocytogenes</em> in the soil environment

National audienceMultiple routes of transmission of Listeria monocytogenes from outdoor environments to foodstuff result in a complex contamination cycle. One of the intriguing facets of Listeria monocytogenes is its ability to adapt its physiology to extremely different habitats such as soil, plants, food processing facilities, foodstuff, gastro intestinal tract of animals and intracellular surroundings. This further suggests the ability to integrate environmental cues in the circuitry of regulation of transcription. Soil is a central habitat in the transmission routes of L. monocytogenes. Soil is a highly heterogeneous habitat that can be characterised by both abiotic (pH, texture, chemistry) and biotic factors. In order to decipher the intrinsic and extrinsic factors that shape the fate of L. monocytogenes in soil, we investigated the response of L. monocytogenes EGD-e in microcosms through a combination of transcriptomic approaches and population dynamics. The fate of L. monocytogenes in soil is dependent on both abiotic and biotic characteristics and the latter have a major impact on the dynamics of the populations of L. monocytogenes in soil. Major transcriptome reshaping is observed in the soil environment where L. monocytogenes recruits its repertoire of transporters and specific pathways to access and utilize the available substrates. The biotic environment further affects transcriptome. The fitness of the populations of L. monocytogenes in soil requires appropriate responses to the biotic environment in which the response regulator AgrA is involved

Metabolism of lactate and sugars by dairy propionibacteria: A review

International audienc

Bactéries environnementales : intérêt biotechnologique et enjeux sanitaires

Diplôme : HD

Involvement of communication systems during the sessile growth of <em>Listeria monocytogenes</em>

International audienc

La biodiversité de la microflore du sol prévient l’implantation de pathogènes alimentaires dans les sols agricoles

Pôle EA MERSNational audienceLa présence dans les agroécosystèmes de bactéries pathogènes pouvant être transmises à l’homme représente un risque sanitaire pour l’ensemble de la filière de production des aliments. Le sol est en effet une zone de transfert potentiel de ces agents pathogènes vers les matières premières agricoles, puis vers les produits agroalimentaires, la plupart du temps dans des produits animaux, mais aussi via des produits végétaux également

Investigation of the adaptive strategies of <em>Listeria monocytogenes</em> in soil/plants mesocosms

National audienceListeria monocytogenes is a foodborne pathogen that affects primarily the vulnerable groups of the population (immune-compromised people, pregnant women, children, and elderly), with low incidence but high mortality. In the last few years, severe outbreaks caused by this bacteria have been associated with the consumption of fresh produce and dairy products. Due to this, soil and plants are considered the first stage of contamination before primary products are processed or transported to the final consumer. Therefore, it is important to understand how L. monocytogenes is able to survive and remain in soil and in association with plants. The present study will focus in elucidating the genetic and proteomic tools used by this bacterium for its prevalence in soil/plant. An analysis of the transcriptome of L. monocytogenes will be carried out in order to investigate the mechanisms of physiological adaptation of the bacteria in response to different circumstances in soil and the rhizosphere. In correlation with these results, a proteomic analysis will be carried out to compare protein expression and transcriptome changes during survival of Listeria monocytogenes in this environment. According to the results a limited number of genes will be selected for further analysis. Deletion mutants will be constructed and their phenotypes will be determined under a range of environmental conditions (soil, rhizosphere, biofilms, and mammalian host). From an ecologic perspective, the consequences of perturbations (lack of oxygen, high and low temperature) of the soil habitat on Listeria monocytogenes population dynamics will be investigated and the shifts in the soil microbiota diversity will be followed by pyrosequencing. These data will give further insights on the correlation between diversity and the ability of organisms to invade habitats under a regimen of perturbations. Results will help to comprehend how this foodborne pathogen can remain in soil to later become a treat for consumers and farm animals’ health

Le système [i]agr[/i] de [i]Listeria monocytogenes[/i] et la croissance en biofilm : revisite des notions de communication, quorum sensing et auto-induction

Communication orale, résuméParmi les mécanismes cellulaires qui participent à la mise en place des biofilms, l’échange de molécules de communication apparaît nécessaire chez de nombreux microorganismes. Listeria monocytogenes est une bactérie ubiquiste responsable de pathologies sévères chez des populations à risque (immunodéprimés, femmes enceintes, personnes âgées) en cas de consommation d’aliments contaminés. Nous avons récemment démontré que le système de communication agr est impliqué au cours de la croissance sessile de cette bactérie (Rieu et al., 2007). Par ailleurs, l’expression du système agr était hétérogène pendant la croissance en biofilm (Rieu et al., 2008) et localisée à sa périphérie en conditions de flux continu. Cette observation va à l’encontre du paradigme du Quorum Sensing qui postule qu’une population de bactéries va développer une réponse concertée lorsque la molécule de communication atteint une concentration seuil. Afin d’étudier les notions de système auto-induit, de Quorum sensing et de communication chez Listeria monocytogenes, nous avons développé une approche combinant l’utilisation de systèmes rapporteurs de type gfp, la cytométrie de flux ainsi que des approches in situ de microscopie. Cette approche vise à étudier l’expression du système agr dans une population et de déterminer l’hétérogénéité de cette expression. La répartition de la fluorescence dans la population est comparée au cours de la croissance planctonique et sessile

Sensitivity to acetic acid, ability to colonize abiotic surfaces and virulence potential of Listeria monocytogenes EGD-e after incubation on parsley leaves.

International audienceAbstract Aim: To investigate how the survival of Listeria monocytogenes on parsley leaves may affect its ability to sustain process-related harsh conditions and its virulence. Methods and Results: Parsley seedlings were spot inoculated with stationary phase cells of L. monocytogenes EGD-e and incubated for 15 days. Each day, bacterial cells were harvested and enumerated, and their ability to survive acetic acid challenge (90 min, pH 4.0), to colonize abiotic surfaces and to grow as biofilms was assessed. After a 3-log decrease over the first 48 h, the population stabilized to about 10(6) CFU g(-1) until the sixth day. After the sixth day, L. monocytogenes was no longer detected, even after specific enrichment. Incubation on parsley leaves affected the ability of L. monocytogenes to survive acetic acid challenge (90 min, pH 4.0) and to adhere to stainless steel although the ability to grow as biofilm was preserved. To further investigate these physiological alterations, the mRNA levels of six target genes (bsh, clpC, groEL, inlA, opuC, prfA) was quantified using reverse transcription qPCR after 5 h of incubation on parsley leaves. A decrease was observed in all but one (bsh) target, including groEL and clpC which are involved in resistance to salt and acid. Moreover, the decrease in the levels of inlA, prfA and opuC transcripts after incubation on parsley suggested a repression of some genes involved in pathogenicity. In vitro assessment of mammalian cell adherence and invasion using Caco-2 cells confirmed the repression of the virulence factor InlA; however, the virulence potential in vivo in the chick embryo model was not affected. Conclusion: Listeria monocytogenes did undergo rapid changes to adapt its physiology to the phyllosphere. Significance and Impact of the Study: This study highlights the physiological changes undergone by L. monocytogenes during/after survival on parsley leaves