FtsZ-independent septal recruitment and function of cell wall remodelling enzymes in chlamydial pathogens.

The nature and assembly of the chlamydial division septum is poorly defined due to the paucity of a detectable peptidoglycan (PG)-based cell wall, the inhibition of constriction by penicillin and the presence of coding sequences for cell wall precursor and remodelling enzymes in the reduced chlamydial (pan-)genome. Here we show that the chlamydial amidase (AmiA) is active and remodels PG in Escherichia coli. Moreover, forward genetics using an E. coli amidase mutant as entry point reveals that the chlamydial LysM-domain protein NlpD is active in an E. coli reporter strain for PG endopeptidase activity (ΔnlpI). Immunolocalization unveils NlpD as the first septal (cell-wall-binding) protein in Chlamydiae and we show that its septal sequestration depends on prior cell wall synthesis. Since AmiA assembles into peripheral clusters, trimming of a PG-like polymer or precursors occurs throughout the chlamydial envelope, while NlpD targets PG-like peptide crosslinks at the chlamydial septum during constriction

Fire impact on forest soils evaluated using near-infrared spectroscopy and multivariate calibration

L'évaluation des propriétés physicochimiques des sols forestiers affectés par des feux a été réalisée en utilisant la spectroscopie proche infra-rouge (SPIR) couplée avec des méthodes chimiométriques. Pour décrire les propriétés du sol, les mesures prises comprennent le carbone organique total sur phase solide, le contenu d'azote total, le carbone organique et l'absorbance spécifique à 254 et 280nm des substances humiques, le carbone organique dans des acides humiques et fulviques, des concentrations de NH4+, Ca2+, Mg2+, K+ et le phosphore en plus des spectres de PIR. Un indice de répétition d'incendies a été défini et calculé selon les régimes de feux affectant des sols. Ce calcul inclut l'occurrence des incendies et le temps écoulé depuis le dernier feu. Cette étude montre que la spectroscopie PIR pourrait être utilisée pour le contrôle de qualité des sols, particulièrement pour la prédiction quantitative du carbone organique total, l'azote total, le carbone organique dans les substances humiques, les concentrations de phosphore, Mg2 +, Ca2 + et NH4 + et des substances humiques UVSA254. Une nouvelle validation dans ce domaine est nécessaire cependant pour une bonne prédictions de K+, du carbone organique dans des acides humiques et fulviques et les substances humiques UVSA280. De plus, la SPIR couplée avec la régression PLS peut aussi être utile pour prévoir l'indice de répétition de feu et pour déterminer sa variabilité spatiale. Aussi cette méthode peut être utilisée pour dresser la carte de secteurs plus ou moins brûlés et pour adapter les techniques de réhabilitation, comme la reconstitution de l'humus avec des enrichissements organiques (composts) ou le reboisement. Finalement, on peut considérer que notre indice de répétition est représentatif de l'état des sols. / The assessment of physico-chemical properties in forest soils affected by fires was evaluated using near infrared reflectance (NIR) spectroscopy coupled with chemometric methods. In order to describe the soil properties, measurements were taken of the total organic carbon on solid phase, the total nitrogen content, the organic carbon and the specific absorbences at 254 and 280nm of humic substances, organic carbon in humic and fulvic acids, concentrations of NH4+, Ca2+,Mg2+, K+ and phosphorus in addition to NIR spectra. Then, a fire recurrence index was defined and calculated according to the different fires extents affecting soils. This calculation includes the occurrence of fires as well as the time elapsed since the last fire. This study shows that NIR spectroscopy could be considered as a tool for soil monitoring, particularly for the quantitative prediction of the total organic carbon, total nitrogen content, organic carbon in humic substances, concentrations of phosphorus, Mg2+, Ca2+ and NH4+ and humic substances UVSA254. Further validation in this field is necessary however, to try and make successful predictions of K+, organic carbon in humic and fulvic acids and the humic substances UVSA280. Moreover, NIR coupled with PLS can also be useful to predict the fire recurrence index in order to determine the spatial variability. Also this method can be used to map more or less burned areas and possibly to apply adequate rehabilitation techniques, like soil litter reconstitution with organic enrichments (industrial composts) or reforestation. Finally, the proposed recurrence index can be considered representative of the state of the soils

Ants in a Labyrinth: A Statistical Mechanics Approach to the Division of Labour

Division of labour (DoL) is a fundamental organisational principle in human societies, within virtual and robotic swarms and at all levels of biological organisation. DoL reaches a pinnacle in the insect societies where the most widely used model is based on variation in response thresholds among individuals, and the assumption that individuals and stimuli are well-mixed. Here, we present a spatially explicit model of DoL. Our model is inspired by Pierre de Gennes' 'Ant in a Labyrinth' which laid the foundations of an entire new field in statistical mechanics. We demonstrate the emergence, even in a simplified one-dimensional model, of a spatial patterning of individuals and a right-skewed activity distribution, both of which are characteristics of division of labour in animal societies. We then show using a two-dimensional model that the work done by an individual within an activity bout is a sigmoidal function of its response threshold. Furthermore, there is an inverse relationship between the overall stimulus level and the skewness of the activity distribution. Therefore, the difference in the amount of work done by two individuals with different thresholds increases as the overall stimulus level decreases. Indeed, spatial fluctuations of task stimuli are minimised at these low stimulus levels. Hence, the more unequally labour is divided amongst individuals, the greater the ability of the colony to maintain homeostasis. Finally, we show that the non-random spatial distribution of individuals within biological and social systems could be caused by indirect (stigmergic) interactions, rather than direct agent-to-agent interactions. Our model links the principle of DoL with principles in the statistical mechanics and provides testable hypotheses for future experiments

Regulatory (pan-)genome of an obligate intracellular pathogen in the PVC superphylum.

Like other obligate intracellular bacteria, the Chlamydiae feature a compact regulatory genome that remains uncharted owing to poor genetic tractability. Exploiting the reduced number of transcription factors (TFs) encoded in the chlamydial (pan-)genome as a model for TF control supporting the intracellular lifestyle, we determined the conserved landscape of TF specificities by ChIP-Seq (chromatin immunoprecipitation-sequencing) in the chlamydial pathogen Waddlia chondrophila. Among 10 conserved TFs, Euo emerged as a master TF targeting >100 promoters through conserved residues in a DNA excisionase-like winged helix-turn-helix-like (wHTH) fold. Minimal target (Euo) boxes were found in conserved developmentally-regulated genes governing vertical genome transmission (cytokinesis and DNA replication) and genome plasticity (transposases). Our ChIP-Seq analysis with intracellular bacteria not only reveals that global TF regulation is maintained in the reduced regulatory genomes of Chlamydiae, but also predicts that master TFs interpret genomic information in the obligate intracellular α-proteobacteria, including the rickettsiae, from which modern day mitochondria evolved

Valeur de l'électrocardiogramme 12-pistes standard de repos pour le diagnostic d'ancien infarctus du myocarde chez le patient porteur d'un stimulateur cardiaque

Nous évaluons la pertinence clinique de signes électrocardiographiques pour le diagnostic d'ancien infarctus auprès de patients porteurs d'un pacemaker.Nous avons étudié 107 patients non-sélectionnés, porteurs de pacemaker, divisés en 3 groupes: 1) groupe contrôle; 2) connu pour ancien infarctus; 3) patient avec resynchronisation pour insuffisance cardiaque sévère. Nos résultats démontrent une bonne spécificité pour la plupart des signes étudiés, au détriment d'une faible sensibilité. Seul le signe de Cabrera se démarque avec une sensibilité à 63.6%. Dans le troisième groupe, on ne retient aucune utilité des signes étudiés. Le diagnostic ECG d'ancien infarctus chez un porteur de pacemaker est difficile mais reste possible, pour autant que l'on connaisse tous les signes électrocardiographiques décrits, car seule une combinaison de ces critères permet d'obtenir une sensibilité et une spécificité acceptables. L'apprentissage et la connaissance de ces signes méritent d'être encouragés en particulier lorsque l'ECG est le seul outil diagnostique à disposition

TorI, a response regulator inhibitor of phage origin in Escherichia coli

The torI gene has been identified by using a genetic multicopy approach as a negative regulator of the torCAD operon that encodes the trimethylamine N-oxide reductase respiratory system in Escherichia coli. The negative effect was due to a previously unidentified small ORF (66 aa) of phage origin that we called torI for Tor inhibition. Overexpression of torI led to an 8-fold decrease of the torCAD operon transcription. This operon is positively regulated, in the presence of trimethylamine N-oxide, by a four-step phosphorelay involving the TorS sensor and the TorR response regulator. Epistatic experiments showed that TorI acts downstream of TorS and needs the presence of TorR. In vitro experiments showed that it is neither a TorR phosphatase nor a histidine kinase inhibitor and that it binds to the effector domain of TorR. Unexpectedly, TorI did not impede TorR DNA binding, and we propose that it may prevent RNA polymerase recruitment to the torC promoter. This study thus reveals a previously uncharacterized class of response regulator inhibitors

Production and elimination of water extractable organic matter in a calcareous soil as assessed by UV/Vis absorption and fluorescence spectroscopy of its fractions isolated on XAD-8/4 resins

International audienceWater extractable organic matter (WEOM) in soil refers to a broad mixture of water-soluble structures recoverable in laboratory through predetermined procedures. In this work, we investigate the mechanisms controlling the occurrence of WEOM fractions isolated on XAD-8/4 resins in a calcareous soil profile as a function of soil depth and seasonal climatic changes. WEOM was roughly collected on a bi-weekly basis during eight consecutive months from an experimental field in the Mediterranean region, south-east of France. Each fraction was analysed for organic carbon content and further characterised using UV/Vis absorbance and 3D fluorescence spectroscopy. The concentrations of hydrophobic (HPOA), transphilic (TPIA) and hydrophilic (HPIA) acids fractions isolated from WEOM followed similar decreasing trends with increasing soil depth, but HPOA decreased most sharply. Specific UV absorbance at 254 nm (SUVA(254)) indicated that HPOA's distribution along the soil column is strongly influenced by the selective removal of aromatic structures, which could be controlled by adsorption mechanisms involving organo-mineral interactions and/or by a shift towards less aromatic precursors in deeper soil layers. 3D spectra of fluorescence revealed the presence of four types of fluorophores: two humic-like (A and C) common to all fractions, one lignin-like (H) specific to HPOA particularly in the upper soil layer, and two protein-like (B1 and B2) specific to TPIA. The importance of the humic component in all fractions was verified by the highly significant correlations between their carbon content and the intensity of humic-like peaks. The aging index (IA/IC) and the fluorescence index (FI), two indicators derived from 3D fluorescence spectra, showed an increase in the microbial input and the degree of humification in HPOA as a function of increasing soil depth. By comparison, IA/IC and FI values in HPIA and TPIA indicated that both fractions were composed almost exclusively of microbial-derived structures, regardless of soil depth. Principal component analysis (PCA) showed the association of temperature (T) to the carbon content in all fractions extracted from the soil layers 0-30 and 30-60 cm, suggesting possible role of microbial activity on their occurrence. The hydraulic regime in soil, controlled by the frequency of rainfall events, affected most significantly HPIA across the entire soil column. PCA, however, failed to identify any consistent trends relating the qualitative properties of WEOM fractions to climatic variables. (C) 2012 Elsevier B.V. All rights reserved