Colloquium : Magnetotactic bacteria: From flagellar motor to collective effects

International audienceMagnetotactic bacteria are swimming microorganisms able to follow magnetic field lines with the help of an organelle called the magnetosome that is made of biomineralized magnetic crystals assembled in a chain. In combination with this ability, these bacteria perform active oxygen sensing to reach the oxic-anoxic transition zone, which is often located in the upper part of the sediment. From a physicist's perspective, magnetotactic bacteria can be seen at the interface between bacterial active matter and magnetic colloids, which gives them unique properties at both the individual and collective levels. In crowded media and/or when they are submitted to external flows, their motion can be efficiently driven by magnetic fields, which leads to surprising effects. In this Colloquium, the different features of magnetotactic bacteria at are reviewed at every scale, from single cell to collective motion, from simple to complex environments, and by emphasizing the differences from other bacterial species or passive magnetic colloids. The Colloquium concludes with a discussion of perspectives on using magnetotactic bacteria in active magnetorheology

Quantification of nonlinear shear moduli in transversely isotropic medium: preliminary study ex vivo and in vivo on muscles

International audienceBackground, Motivation and Objective Acoustoelasticity theory (AET) describes propagation of shear wave (SW) in uniaxially stressed medium and allows to retrieve nonlinear (NL) elastic coefficients of tissues. Regarding clinical diagnosis, studies showed that NL response of material’s during mechanical tests is useful for the diagnostic of cancerous tissues. Our hypothesis is that NL parameters can be representative of the state of muscles. In previous work, AET in transverse isotropic medium was developed leading to 9 different configurations (cfgs.) (stress axis vs. fibers axis vs. SW polarization axis vs. SW propagation axis). In this work we propose to use 4 cfgs. (Fig.) to quantify these NL parameters ex vivo and in vivo. Statement of Contribution/Methods Ex vivo experiments were conducted on 4 ilio psoas muscles from 2 pigs. During step-by-stepmechanical testing, SWS was quantified with a 6 MHz central frequency probe (SL10-2) driven by ultrafast ultrasound (US) device (Mach30, Supersonic Imagine). From the stress (σ) - strain (ε) curve obtained with the traction device (Instron 5969), the Young’s modulus parallel (E//) to fibers was retrieve. Then from 3 different cfgs. (3, 5 and 7), NL coefficients A, H, K were quantified. In vivo experiments were performed with volunteers on biceps braachi after approval of the local ethic committee. Volunteers were seated with the arm fixed to an ergometer in order to control the muscle contraction and σ generated during stretching. By using a dedicated US sequence [1], E// was quantified when the probe was // to fibers axis at rest as well as shear moduli μ⊥ and μ//. Then axial ε of the muscle and SWS for two cfgs. (3 and 9) were measured every 5° increment of stretching angle, from 90° to 135° of elbow extension. ε was retrieved by comparing two US images between two stretching steps and allowed to compute the local σ by applying the Hooke’s law. At last since only 2 acquisitions cfgs. are possible in vivo a combination (X and Y) of the NL coefficient was calculated and compared with the ex vivo data. Results/Discussion In ex vivo muscle, A, H, K were retrieved thanks to the 3 possible experimentations cfgs. In vivo, presented for only one volunteer in Fig., X and Y were retrieved and are in good accordance with them obtained ex vivo. This works paves the way to better understand muscle biomechanics and physics during contraction and force productio

Dynamique non linéaire d'un tube avec butée annulaire radiale. Analyse numérique et expérimentale.

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Tepidibacter aestuarii sp. nov., isolated from the Bach Dang Estuary, Haiphong, Vietnam

International audienceA mesophilic, anaerobic, endospore-forming, fermentative bacterium designated strain 8C15b T was isolated from bank sediment of the Bach Dang Estuary, Haiphong, Vietnam. The Bach Dang Estuary, where Haiphong harbour is located, is subject to strong anthropogenic influence, resulting in high concentrations of black carbon and heavy metals. Strain 8C15b T grew optimally at 30 °C, pH 7.5 and with 2.5 % (w/v) NaCl. The main cellular fatty acids consisted of iso-C 15 : 0 (51 %), iso-C 15:1 ω7 c (32 %) and iso-C 13 : 0 (5 %). Genomic considerations of strain 8C15b T and comparisons with the phylogenetically closest strains of the genus Tepidibacter provide evidence that Tepidibacter thalassicus SC562 T (=DSM 15285 T ), Tepidibacter formicigenes DV1184 T (=DSM 15518 T ), Tepidibacter mesophilus B1 T (=JCM 16806 T ) and strain 8C15b T could be differentiated at the species level. We propose the name Tepidibacter aestuarii sp. nov. for the type strain 8C15b T (=JCM 35983 T =KCTC 25692 T ). Finally, the nickel-tolerance properties of strain 8C15b T are highlighted in this study

Plakins are involved in the regulation of centrosome position in polarized epithelial cells

International audienceAbstract Background Information The control of epithelial cell polarity is key to their function. Its dysregulation is a major cause of tissue transformation. In polarized epithelial cells,the centrosome is off‐centred toward the apical pole. This asymmetry determines the main orientation of the microtubule network and intra‐cellular traffic. However, the mechanism regulating centrosome positioning at the apical pole of polarized epithelial cells is still poorly undertood. Results In this study we used transcriptomic data from breast cancer cells to identify molecular changes associated with the different stages of tumour transformation. We correlated these changes with variations in centrosome position or with cell progression along the epithelial‐to‐mesenchymal transition (EMT), a process that involves centrosome repositioning. We found that low levels of epiplakin, desmoplakin and periplakin correlated with centrosome mispositioning in cells that had progressed through EMT or tissue transformation. We further tested the causal role of these plakins in the regulation of centrosome position by knocking down their expression in a non‐tumorigenic breast epithelial cell line (MCF10A). The downregulation of periplakin reduced the length of intercellular junction, which was not affected by the downregulation of epiplakin or desmoplakin. However, down‐regulating any of them disrupted centrosome polarisation towards the junction without affecting microtubule stability. Conclusions Altogether, these results demonstrated that epiplakin, desmoplakin and periplakin are involved in the maintenance of the peripheral position of the centrosome close to inter‐cellular junctions. They also revealed that these plakins are downregulated during EMT and breast cancer progression, which are both associated with centrosome mispositioning. Significance These results revealed that the down‐regulation of plakins and the consequential centrosome mispositioning are key signatures of disorganised cytoskeleton networks, inter‐cellular junction weakening, shape deregulation and the loss of polarity in breast cancer cells. These metrics could further be used as a new readouts for early phases of tumoral development

Transposon sequencing reveals the essential gene set and genes enabling gut symbiosis in the insect symbiont <i>Caballeronia insecticola</i>

International audienceCaballeronia insecticola is a bacterium belonging to the Burkholderia genus sensu lato, which is able to colonize multiple environments like soils and the gut of the bean bug Riptortus pedestris. We constructed a saturated Himar1 mariner transposon library and revealed by transposon-sequencing that 498 protein-coding genes constitute the essential genome of Caballeronia insecticola for growth in free-living conditions. By comparing essential gene sets of Caballeronia insecticola and seven related Burkholderia s.l. strains, only 120 common genes were identified, indicating that a large part of the essential genome is strain-specific. In order to reproduce specific nutritional conditions that are present in the gut of Riptortus pedestris, we grew the mutant library in minimal media supplemented with candidate gut nutrients and identified several condition-dependent fitness-defect genes by transposon-sequencing. To validate the robustness of the approach, insertion mutants in six fitness genes were constructed and their growth deficiency in media supplemented with the corresponding nutrient was confirmed. The mutants were further tested for their efficiency in Riptortus pedestris gut colonization, confirming that gluconeogenic carbon sources, taurine and inositol, are nutrients consumed by the symbiont in the gut. Thus, our study provides insights about specific contributions provided by the insect host to the bacterial symbiont

Manufacturing of 2507 super duplex stainless steel by laser powder-directed energy deposition: process optimization and microstructure analyses

International audienceThis paper presents a thorough manufacturability study of 2507 super duplex stainless steel (SDSS) produced by the Laser Powder-Directed Energy Deposition (LP-DED) process. First, experimental observations on single-track surface morphology and geometrical characteristics are described. Then, dimensional and porosity analyses of thin walls and bulk samples are presented and discussed in order to identify the optimal process parameter combinations, from a process point of view, for further characterizations to determine the general properties of LP-DED-printed samples. Finally, the results obtained on wrought steel of the same grade are compared to those of the printed material in terms of microstructure, texture, and ferrite/austenite ratio. A set of meticulously chosen process parameters with regard to the process and the machine (nozzle size, maximum power deliverable) gives the optimal results for the as-built LP-DED material in terms of porosity and microstructure quality but with smaller grains (irrespective of the phase studied) and a higher proportion of ferrite (about 75%)

Dark Matter distinguished by skewed microlensing in the "Dragon Arc"

International audienceMicrolensed stars recently discovered by JWST & HST follow closely the winding critical curve of A370 along all sections of the ``Dragon Arc" traversed by the critical curve. These transients are fainter than $m_{AB}>26.5$, corresponding to the Asymptotic Giant Branch (AGB) and microlensed by diffuse cluster stars observed with $\simeq 18M_\odot/pc^2$, or about $\simeq 1$% of the projected dark matter density. Most microlensed stars appear along the inner edge of the critical curve, following an asymmetric band of width $\simeq 4$kpc that is skewed by $-0.7\pm0.2$kpc. Some skewness is expected as the most magnified images should form along the inner edge of the critical curve with negative parity, but the predicted shift is small $\simeq -0.04$kpc and the band of predicted detections is narrow, $\simeq 1.4$kpc. Adding CDM-like dark halos of $10^{6-8}M_\odot$ broadens the band as desired but favours detections along the outer edge of the critical curve, in the wrong direction, where sub-halos generate local Einstein rings. Instead, the interference inherent to ``Wave Dark Matter" as a Bose-Einstein condensate ($\psi$DM) forms a symmetric band of critical curves that favours negative parity detections. A de Broglie wavelength of $\simeq 10$pc matches well the observed $4$kpc band of microlenses and predicts negative skewness $\simeq -0.6$kpc, similar to the data. The implied corresponding boson mass is $\simeq 10^{-22}$eV, in good agreement with estimates from dwarf galaxy cores when scaled by momentum. Further JWST imaging may reveal the pattern of critical curves by simply ``joining the dots" between microlensed stars, allowing wave corrugations of $\psi$DM to be distinguished from CDM sub-halo

Blinding scheme for the scale-dependence bias signature of local primordial non-Gaussianity for DESI 2024

International audienceThe next generation of spectroscopic surveys is expected to achieve an unprecedented level of accuracy in the measurement of cosmological parameters. To avoid confirmation bias and thereby improve the reliability of these results, blinding procedures become a standard practice in the cosmological analyses of such surveys. Blinding is especially crucial when the impact of observational systematics is important relative to the cosmological signal, and a detection of that signal would have significant implications. This is the case for local primordial non-gaussianity, as probed by the scale-dependent bias of the galaxy power spectrum at large scales that are heavily sensitive to the dependence of the target selection on the imaging quality, known as imaging systematics. We propose a blinding method for the scale-dependent bias signature of local primordial non-gaussianity at the density field level which consists in generating a set of weights for the data that replicate the scale-dependent bias. The applied blinding is predictable, and can be straightforwardly combined with other catalog-level blinding procedures that have been designed for the baryon acoustic oscillation and redshift space distortion signals. The procedure is validated through simulations that replicate data from the first year of observation of the Dark Energy Spectroscopic Instrument, but may find applications to other upcoming spectroscopic surveys

Probing strangeness hadronization with event-by-event production of multistrange hadrons

International audienceThis Letter presents the first measurement of event-by-event fluctuations of the net number (difference between the particle and antiparticle multiplicities) of multistrange hadrons $\Xi^-$ and $\overline{\Xi}^+$ and its correlation with the net-kaon number using the data collected by the ALICE Collaboration in pp, p$-$Pb, and Pb$-$Pb collisions at a center-of-mass energy per nucleon pair $\sqrt{s_{\mathrm{NN}}}=5.02\ \mathrm{TeV}$. The statistical hadronization model with a correlation over three units of rapidity between hadrons having the same and opposite strangeness content successfully describes the results. On the other hand, string-fragmentation models that mainly correlate strange hadrons with opposite strange quark content over a small rapidity range fail to describe the data