Probing multilayer stack reflectors by low coherence interferometry in extreme ultraviolet

International audienceWe use low coherence interferometry to investigate the depth structure of a complex multilayer stack reflector. The probing instrument is an interferometer based on a Fresnel's bi-mirror illuminated by relatively wide-band synchrotron undulator light near 13.5 nm. Simulations clearly confirm that our test object generates two back propagated signals that behave as if reflected on two effective planes. First results in this spectral range may open the way to a new physical approach to extreme ultraviolet sample characterization in the form of line-scan optical coherence tomography

Anaerobutyricum hallii promotes the functional depletion of a food carcinogen in diverse healthy fecal microbiota

IntroductionAnaerobutyricum hallii is a human gut commensal that transforms the heterocyclic amine 2-amino-1-methyl-6-phenylimidazo [4,5-b] pyridine (PhIP), a carcinogen from cooked meat. The transformation mechanism involves the microbial production of acrolein from glycerol, and its conjugation with PhIP, thus blocking its mutagenic potential. A potential cancer prevention strategy could therefore involve supplementing complex human microbial communities with metabolically competent bacteria such as A. hallii that can deplete PhIP. However, it has not been established how the proportion of A. hallii in diverse healthy human gut microbial communities relates to functional capacity for PhIP transformation and, moreover, how supplementing microbiomes with A. hallii affects this function.MethodsIn this study, shotgun metagenomics was used to study taxonomic profiling, the abundance of glycerol/diol dehydratase (gdh)-harboring taxa, the proportion of resident A. hallii, and the reconstruction of A. hallii population genomes in the fecal samples of 20 healthy young adult donors. Furthermore, the influence of supplementing 106 cells/mL of A. hallii DSM 3353 with diluted fecal microbiota was characterized.Results and discussionSix microbiota were assigned to Bacteroides, nine to Prevotella, and five to Ruminococcus by enterotype-associated clustering. The total number of gdh copies in the 20 fecal microbiota expressed per 1010 bacterial cells ranged between 1.32 × 108 and 1.15 × 109. Eighteen out of the 20 donors were dominated by A. hallii, representing between 33% and 94% of the total gdh relative abundance of the samples. The microbiota with low A. hallii abundance (i.e., with a relative abundance < 1%) transformed less PhIP than the microbiota with high A. hallii abundance (i.e., with a relative abundance > 1%). Furthermore, supplementing the low-A. hallii-abundant microbiota with glycerol significantly increased the PhIP transformation capacity after 6 h while reducing total short-chain fatty acid (SCFA) levels, which is most likely due to acrolein production. Although acetate decreased in all microbiota with glycerol and with the combination of glycerol and A. hallii, for most of the microbiomes, butyrate production increased over time. Thus, for a significant number of diverse healthy human fecal microbiomes, and especially when they have little of the taxa to start with, supplementing A. hallii increases PhIP transformation. These findings suggest the need to test in vivo whether supplementing microbiomes with A. hallii reduces PhIP exposure

Fabrication of high aspect ratio tungsten nanostructures on ultrathin c-Si membranes for extreme UV applications

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Light interference detection on-chip by integrated SNSPD counters

A SWIFTS device (Stationary Wave Integrated Fourier Transform Spectrometer) has been realized with an array of 24 Superconducting Nanowire Single Photon Detectors (SNSPD), on-chip integrated under a Si3N4 monomode rib-waveguide interferometer. Colored light around 1.55μm wavelength is introduced through end-fire coupling, producing a counter-propagative stationary interferogram over the 40nm wide, 120nm spaced, 4nm thick epi-NbN nanowire array. Modulations in the source bandwidth have been detected using individual waveguide coupled SNSPDs operating in single photon counting mode, which is a step towards light spectrum reconstruction by inverse Fourier transform of the stationary wave intensity. We report the design, fabrication process and in-situ measurement at 4.2K of light power modulation in the interferometer, obtained with variable laser wavelength. Such micro-SWIFTS configuration with 160nm sampling period over 3.84μm distance allows a spectral bandwidth of 2μm and a wavelength resolution of 170nm. The light interferences direct sampling ability is unique and raises wide interest with several potential applications like fringe-tracking, metrology, cryptography or optical tomography

Terroir Is the Main Driver of the Epiphytic Bacterial and Fungal Communities of Mango Carposphere in Reunion Island

International audienceThe diversity of both bacterial and fungal communities associated with mango surface was explored using a metabarcoding approach targeting fungal ITS2 and bacterial 16S (V3-V4) genomic regions. Fruits were collected in Reunion Island from two different orchards according to a sampling method which allowed the effect of several pre-harvest factors such as geographical location (terroir), cultivars, fruit parts, tree position in the plot, fruit position on the tree (orientation and height), as well as the harvest date to be investigated. A total of 4,266,546 fungal and 2,049,919 bacterial reads were recovered then respectively assigned to 3,153 fungal and 24,087 to bacterial amplicon sequence variants (ASVs). Alpha and beta diversity, as well as differential abundance analyses revealed variations in both bacterial and fungal communities detected on mango surfaces depended upon the studied factor. Results indicated that Burkholderiaceae (58.8%), Enterobacteriaceae (5.2%), Pseudomonadaceae (4.8%), Sphingomonadaceae (4.1%), Beijerinckiaceae (3.5%), and Microbacteriaceae (3.1%) were the dominant bacterial families across all samples. The majority of fungal sequences were assigned to Mycosphaerellaceae (34.5%), Cladosporiaceae (23.21%), Aureobasidiaceae (13.09%), Pleosporaceae (6.92%), Trichosphaeriaceae (5.17%), and Microstromatales_fam_Incertae_sedis (4.67%). For each studied location, mango fruit from each cultivar shared a core microbiome, and fruits of the same cultivar harvested in two different locations shared about 80% fungal and bacterial family taxa. The various factors tested in this study affected bacterial and fungal taxa differently, suggesting that some taxa could act as geographical (terroir) markers and in some cases as cultivar fingerprints. The ranking of the factors investigated in the present study showed that in decreasing order of importance: the plot (terroir), cultivar, fruit parts, harvest date and the position of the fruits are respectively the most impacting factors of the microbial flora, when compared to the orientation and the fruit position (height) on the tree. Overall, these findings provided insights on both bacterial and fungal diversity associated with the mango surface, their patterns from intra-fruit scale to local scale and the potential parameters shaping the mango microbiota

Fabrication of Buckling Free Ultrathin Silicon Membranes by Direct Bonding with Thermal Difference

An innovative method to fabricate large area (up to several squared millimeters) ultrathin (100 nm) monocrystalline silicon (Si) membranes is described. This process is based on the direct bonding of a silicon-on-insulator wafer with a preperforated silicon wafer. The stress generated by the thermal difference applied during the bonding process is exploited to produce buckling free silicon nanomembranes of large areas. The thermal differences required to achieve these membranes (≥1 mm²) are estimated by analytical calculations. An experimental study of the stress achievable by direct bonding through two specific surface preparations (hydrophobic or hydrophilic) is reported. Buckling free silicon nanomembranes secured on a 2 × 2 cm² frame with lateral dimensions up to 5 × 5 mm² are successfully fabricated using the optimized direct bonding process. The stress estimated by theoretical analysis is confirmed by Raman measurements, while the flatness of the nanomembranes is demonstrated by optical interferometry. The successful fabrications of high resolution (50 nm half pitch) tungsten gratings on the silicon nanomembranes and of focused ion beam milling nanostructures show the promising potential of the Si membranes for X-ray optics and for the emerging nanosensor market

Overlay measurements by Mueller polarimetry in back focal plane

International audienceAngle resolved Mueller polarimetry implemented as polarimetric imaging of a back focal plane of a high NA microscope objective has already demonstrated a good potential for CD metrology. Here we present the experimental and numerical results indicating that this technique may also be competitive for the measurements of overlay error delta. A series of samples of superimposed gratings with well controlled overlay errors have been manufactured and measured with the angle resolved Mueller polarimeter. The overlay targets were 20-mu m wide. When the overlay error is delta is equal to 0, absolute values of elements of real 4x4 Mueller matrix M are invariant by matrix transposition. Otherwise this symmetry breaks down. Consequently, we define the following overlay estimator matrix as E = |M| - |M|(t). The simulations show that matrix element E-14 is the most sensitive to the overlay error. The scalar estimator of E-14 was calculated by averaging the pixel values over a specifically chosen mask. This estimator is found to vary linearly with d for overlay values up to 50 nm. Our technique allows entering small overlay marks (down to 5-mu m wide). Only one target measurement is needed for each overlay direction. The actual overlay value can be determined without detailed simulation of the structure provided two calibrated overlay structures are available for each direction

GABA Production by Human Intestinal Bacteroides spp.: Prevalence, Regulation, and Role in Acid Stress Tolerance

The high neuroactive potential of metabolites produced by gut microbes has gained traction over the last few years, with metagenomic-based studies suggesting an important role of microbiota-derived γ-aminobutyric acid (GABA) in modulating mental health. Emerging evidence has revealed the presence of the glutamate decarboxylase (GAD)-encoding gene, a key enzyme to produce GABA, in the prominent human intestinal genus Bacteroides. Here, we investigated GABA production by Bacteroides in culture and metabolic assays combined with comparative genomics and phylogenetics. A total of 961 Bacteroides genomes were analyzed in silico and 17 metabolically and genetically diverse human intestinal isolates representing 11 species were screened in vitro. Using the model organism Bacteroides thetaiotaomicron DSM 2079, we determined GABA production kinetics, its impact on milieu pH, and we assessed its role in mitigating acid-induced cellular damage. We showed that the GAD-system consists of at least four highly conserved genes encoding a GAD, a glutaminase, a glutamate/GABA antiporter, and a potassium channel. We demonstrated a high prevalence of the GAD-system among Bacteroides with 90% of all Bacteroides genomes (96% in human gut isolates only) harboring all genes of the GAD-system and 16 intestinal Bacteroides strains producing GABA in vitro (ranging from 0.09 to 60.84 mM). We identified glutamate and glutamine as precursors of GABA production, showed that the production is regulated by pH, and that the GAD-system acts as a protective mechanism against acid stress in Bacteroides, mitigating cell death and preserving metabolic activity. Our data also indicate that the GAD-system might represent the only amino acid-dependent acid tolerance system in Bacteroides. Altogether, our results suggest an important contribution of Bacteroides in the regulation of the GABAergic system in the human gut