Nicolas Pelletier

Genomic, proteomic, and transcriptomic analysis of virulent and avirulent Rickettsia prowazekii reveals its adaptive mutation capabilities

Rickettsia prowazekii, the agent of epidemic typhus, is an obligate intracellular bacterium that is transmitted to human beings by the body louse. Several strains that differ considerably in virulence are recognized, but the genetic basis for these variations has remained unknown since the initial description of the avirulent vaccine strain nearly 70 yr ago. We use a recently developed murine model of epidemic typhus and transcriptomic, proteomic, and genetic techniques to identify the factors associated with virulence. We identified four phenotypes of R. prowazekii that differed in virulence, associated with the up-regulation of antiapoptotic genes or the interferon I pathway in the host cells. Transcriptional and proteomic analyses of R. prowazekii surface protein expression and protein methylation varied with virulence. By sequencing a virulent strain and using comparative genomics, we found hotspots of mutations in homopolymeric tracts of poly(A) and poly(T) in eight genes in an avirulent strain that split and inactivated these genes. These included recO, putative methyltransferase, and exported protein. Passage of the avirulent Madrid E strain in cells or in experimental animals was associated with a cascade of gene reactivations, beginning with recO, that restored the virulent phenotype. An area of genomic plasticity appears to determine virulence in R. prowazekii and represents an example of adaptive mutation for this pathogen.

Specific recognition of the major capsid protein of Acanthamoeba polyphaga mimivirus by sera of patients infected by Francisella tularensis.

Francisella tularensis, a Gram-negative cocobacillus responsible for tularemia, especially severe pneumonia, is a facultative intracellular bacterium classified as a biological agent of category A. Acanthamoeba polyphaga mimivirus (APM) is a recently discovered giant virus suspected to be an agent of both community- and hospital-acquired pneumonia. During specificity testing of antibody to APM detection, it was observed that nearly all patients infected by F. tularensis had elevated antibody titers to APM. In the present study, we investigated this cross-reactivity by immunoproteomics. Apart from the detection of antibodies reactive to new immunoreactive proteins in patients infected by F. tularensis, we showed that the sera of those patients recognize specifically two proteins of APM: the capsid protein and another protein of unknown function. No common protein motif can be detected in silico based on genome analysis of the involved protein. Furthermore, this cross-reactivity was confirmed with the recombinant capsid protein expressed in Escherichia coli. This emphasizes the pitfalls of a serological diagnosis of pneumonia.

Fast Psychrometers as New SU-8 Based Microsystems

In this paper, a new approach to designing fast micro-psychrometers devoted to measuring relative humidity is presented. Such devices are based on a planar thermopile fitted with an appropriate set of microchannels arranged for monitoring the evaporation process as a Seebeck voltage. They are fabricated out of a glass substrate, sputtered metals, and near vertical side walls made of SU-8, according to standard microtechnology processes for MEMs. Considering classical psychrometers, the new design is aimed at reducing both size and response time. Thus, besides being far less invasive than a standard unit, fast measurements (tau=5 s) are enabled. A straightforward modeling, aimed at deriving the relative humidity, is given with a view to integrating the signal conditioner. As regards validation, a prototype is calibrated and compared to a reference probe, and a discussion on its enhancement is also presented

Integrated Mach-Zehnder interferometer on SU-8 polymer for designing pressure sensors

This paper describes a new integrated pressure sensor based on a Mach-Zehnder (MZ) interferometer made of SU-8 polymer. Such a device is designed with a view to working in a standard intensity modulation scheme. To this end, the device takes advantage of a differential measurement thanks to a sensing arm of the MZ structure arranged upon a thin membrane actuated by the pressure to be dealt with, while the second arm allows for a reference signal. The combination of both signals out of the optimized structure of the interferometer allows us to detect any change in the optical path as a result of the applied pressure. A prototype is characterized by way of a specific optical bench allowing an efficient end-fire coupling into the sensor. Practical results prove such a design to delineate a promising measurement approach

Integrated optical Mach-Zehnder on SU-8 polymer for designing thermal sensors

A new approach to designing heat sensors is presented. The basic principle relies on the differential thermal behavior regarding both active arms of a micro Mach-Zehnder interferometer (MZI). Based on modeling results, an experimental sensor is realised as an integrated device made up of SU-8 polymer mounted on a standard silicon wafer. When subjected to a radiant source, such as laser light (980 nm), injected across the cleaved input face of the MZI, the significant change of output signal allows us to consider a new approach to measuring radiant heat flow rate. Experimental results are given regarding the obtained phase shift against the subjected thermal power. According to the modeling results, one can expect new highly sensitive devices to be developed in the next coming years, with numerous prospective industrial applications.

Versatile SOG/SU-8/fluorinated SU-8 rib optical waveguides as microsystems: single-mode TE 00 -TM 00 straight waveguides, S-bends, Y-junctions, Mach-Zehnder interferometers

The authors present a successful design, realisation and characterisation of single-mode TE00-TM00 rib optical waveguides composed of SU-8/SOG polymers subjected (or not) to an apt fluorine-plasma treatment. Such techniques based on radiofrequency fluorine plasma treatment (CF4) proved to strongly modify the properties regarding optical losses due to propagation (selectivity on the polarisation modes, and so on). After realisation of sundry single mode optical waveguides (straight, S-bends, Y-junctions, Mach-Zehnder (MZ) interferometers), the linear absorption coefficient of energy αTE-TM of such rib waveguides have been measured for both optical modes TE00 and TM00 on Si/SiO2/SU-8 structures that yield optical losses of 1.36 dB/cm and 2.01 dB/cm respectively. Optical losses ascribed to Si/SiO2/SOG/SU-8 microstructures have been evaluated to 2.33 dB/cm and 2.95 dB/cm for both polarisations. Concerning the fluorine plasma treatment on SU-8 polymer waveguides, the optical losses regarding Si/SiO2/Fluorinated SU-8 microstructures have been evaluated to 1.25 dB/cm for TE00 polarisation, having then been reduced by 0.11 dB/cm, compared to propagation in pure SU-8. Moreover, such a specific plasma treatment leads to a substantial selectivity on optical polarisation states regarding the TM00 optical mode which has been advantageously used. Thereby, integrated optical polarizers have been achieved on fluorinated SU-8. Hence, as a crucial step for designing polymer components devoted to microsensors applications, the SU-8 (fluorinated or not) polymer appears as a promising candidate for integrated optics with low optical losses.