17 research outputs found
Gap, a mycobacterial specific integral membrane protein, is required for glycolipid transport to the cell surface
The cell envelope of mycobacteria is a complex multilaminar structure that protects the cell from stresses encountered in the environment, and plays an important role against the bactericidal activity of immune system cells. The outermost layer of the mycobacterial envelope typically contains species-specific glycolipids. Depending on the mycobacterial species, the major glycolipid localized at the surface can be either a phenolglycolipid or a peptidoglycolipid (GPL). Currently, the mechanism of how these glycolipids are addressed to the cell surface is not understood. In this study, by using a transposon library of Mycobacterium smegmatis and a simple dye assay, six genes involved in GPLs synthesis have been characterized. All of these genes are clustered in a single genomic region of approximately 60 kb. We show by biochemical analyses that two non-ribosomal peptide synthetases, a polyketide synthase, a methyltransferase and a member of the MmpL family are required for the biosynthesis of the GPLs backbone. Furthermore, we demonstrate that a small integral membrane protein of 272 amino acids named Gap (gap: GPL addressing protein) is specifically required for the transport of the GPLs to the cell surface. This protein is predicted to contain six transmembrane segments and possesses homologues across the mycobacterial genus, thus delineating a new protein family. This Gap family represents a new paradigm for the transport of small molecules across the mycobacterial envelope, a critical determinant of mycobacterial virulence
Impact of long-range transport over the Atlantic Ocean on Saharan dust optical and microphysical properties based on AERONET data
Arid regions are a major source of mineral dust aerosol.
Transport from these sources can have a great impact on aerosol climatology
in distant regions. In order to assess the impact of dust on climate we must
understand how dust properties change after long distance transport from
sources. This study addresses the changes in columnar aerosol properties when
mineral dust outbreaks from western Africa arrive over the eastern Caribbean
after transport across the Atlantic Ocean, a transit of 5–7 days. We use
data from the NASA Aerosol Robotic Network (AERONET) located at five
Caribbean and two western Africa sites to characterize changes in columnar
aerosol properties: aerosol optical depth (AOD), size distribution, single
scattering albedo, and refractive indexes. We first characterized the local
aerosol climatology at each site and then using air mass back trajectories we
identified those days when trajectories over Caribbean sites back-tracked to
western Africa. Over the period 1996–2014 we identify 3174 days, an average of
167Â days per year, when the air mass over the Caribbean sites could be linked
to at least one of the two western Africa sites. For 1162 of these days, AOD
data are available for the Caribbean sites as well as for the corresponding
western Africa sites about 5–7 days earlier, when the air mass passed over
these sites. We identified dust outbreaks as those air masses yielding
AOD  ≥  0.2 and an Ångström exponent below 0.6. On this basis of
the total 1162Â days, 484Â meet the criteria for mineral dust outbreaks. We
observe that the AOD at 440 nm decreases by about 0.16 or 30 % during
transport. The volume particle size distribution shows a similar decrease in
the volume concentration, mainly in the coarse mode. The single scattering
albedo, refractive indexes, and asymmetry factor remain unchanged. The
difference in the effective radius over western Africa sites with respect to
Caribbean sites ranges between 0 and −0.3 µm. Finally we conclude
that in about half of the cases only non-spherical dust particles are present
in the atmosphere over the western Africa and Caribbean sites, while in the other
cases dust particles were mixed with other types of aerosol particles.</p
Caractérisations physico-chimiques et électriques de films ferroélectriques synthétisés par voie hydrothermale
National audienc
Micromachined temperature calibration tool for contact Scanning Thermal Microscope probes
Local thermal probing has become a major tool for studying transport phenomena at micro and nanoscale levels, detecting hot spots and failures of microelectronic devices or measuring surface temperature distribution at these scales. If contact point measurement of a local tip is expected to provide the best spatial resolution, the fundamental aspect of the interaction between the probe tip and the sample remains the key point on which any quantitative measurement relies. We focus on the calibration procedure that will allow measuring the thermal response (error) of a contact probe used for temperature measurement on a surface. For this purpose, a micro-hotplate made of platinum heater suspended on thin silicon nitride (SiN) membrane represents an interesting tool. The objective is to develop heated reference samples with localized temperature sensors embedded on its surface to probe the temperature during the probe contact. We report on the thermal design of low-power calibration chip and the first results obtained when contacting wire based micro-Thermocouple Scanning Thermal Microscope (SThM) probes. © 2015 IEEE
Calibration Tools for Scanning Thermal Microscopy Probes Used in Temperature Measurement Mode
International audienc
A specific lipopentapeptide produced by Mycobacterium avium subp. Paratuberculosis to develop useful diagnostic tools
National audienc
Investigations of room temperature bolometers for THz applications
Abstruct- We investigate in this work the perlbrmance of two conligurations of room temperature bolometers dedicated to THz applications. Fabrication processes, noise level, sensitivity and resolution characterizations ùre presented. Results emphasize the cllicicncy of the proposed approach