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The striking feature of the ubiquitous protein EfTu (Thermo unstable ribosomal Elongation factor) is its moonlighting (multifunctional) activity. Beyond its function at the ribosomal level it should be exported to the bacterial surface and act as an environmental sensor. In Bacillus cereus , and other cutaneous bacteria, it serves as a Substance P (SP) receptor and is essential for bacterial adaptation to the host. However, the modus operandi of EfTu as a bacterial sensor remains to be investigated. Studies realized by confocal and transmission electron microscopy revealed that, in the absence of an exogenous signal, EfTu is not exposed on the bacterial surface but is recruited under the effect of SP. In addition, SP acts as a transcriptional regulator of the tuf gene encoding for EfTu. As observed using gadolinium chloride, an inhibitor of membrane mechanosensitive channels (Msc), Msc control EfTu export and subsequently the bacterial response to SP both in terms of cytotoxicity and biofilm formation activity. Microscale thermophoresis revealed that in response to SP, EfTu can form homopolymers. This event should occur after EfTu export and, as shown by proteo-liposome reconstruction studies, SP appears to promote EfTu polymers association to the membrane, leading subsequently to the bacterial response. Molecular modeling suggests that this mechanism should involve EfTu unfolding and insertion into the bacterial cytoplasmic membrane, presumably through formation of homopolymers. This study is unraveling the original mechanism action of EfTu as a bacterial sensor but also reveals that this protein should have a broader role, including in eukaryotes.

Subdued lighting The diffuse light permeating intergalactic space contains precious information about the early Universe. Exactly what information is a matter of conjecture: light from the first stars, perhaps, or direct starlight from later galaxies? Gamma-ray observations of two distant active galaxies with HESS, the High Energy Stereoscopic System array in Namibia, reveal that the diffuse light intensity is lower than expected from recent claims. This suggests that the Universe is more transparent to γ-rays than was thought, and favours galaxies as the dominant light source, rather than early stars. The diffuse extragalactic background light consists of the sum of the starlight emitted by galaxies through the history of the Universe, and it could also have an important contribution from the ‘first stars’, which may have formed before galaxy formation began. Direct measurements are difficult and not yet conclusive, owing to the large uncertainties caused by the bright foreground emission associated with zodiacal light 1 . An alternative approach 2 , 3 , 4 , 5 is to study the absorption features imprinted on the γ-ray spectra of distant extragalactic objects by interactions of those photons with the background light photons 6 . Here we report the discovery of γ-ray emission from the blazars 7 H 2356 - 309 and 1ES 1101 - 232, at redshifts z = 0.165 and z = 0.186, respectively. Their unexpectedly hard spectra provide an upper limit on the background light at optical/near-infrared wavelengths that appears to be very close to the lower limit given by the integrated light of resolved galaxies 8 . The background flux at these wavelengths accordingly seems to be strongly dominated by the direct starlight from galaxies, thus excluding a large contribution from other sources—in particular from the first stars formed 9 . This result also indicates that intergalactic space is more transparent to γ-rays than previously thought.

Central issues Events at the centre of our Galaxy are key to our understanding of high-energy processes in the Universe, since it contains examples of virtually every type of exotic object known to astronomers. The very-high-energy γ-ray emission from the Galactic Centre region has now been measured using HESS, the High Energy Stereoscopic System recently constructed in Namibia, South West Africa. HESS operates at energies above the regime accessible to satellite-based detectors, taking γ-ray astronomy into new territory. The results show that these clouds are glowing in very high energy γ-rays. The glow is caused by constant bombardment of the clouds by cosmic rays — probably protons and nuclei — produced close to the central black hole or in the expanding blast waves of supernova explosions. The source of Galactic cosmic rays (with energies up to 10 15  eV) remains unclear, although it is widely believed that they originate in the shock waves of expanding supernova remnants 1 , 2 . At present the best way to investigate their acceleration and propagation is by observing the γ-rays produced when cosmic rays interact with interstellar gas 3 . Here we report observations of an extended region of very-high-energy (> 10 11  eV) γ-ray emission correlated spatially with a complex of giant molecular clouds in the central 200 parsecs of the Milky Way. The hardness of the γ-ray spectrum and the conditions in those molecular clouds indicate that the cosmic rays giving rise to the γ-rays are likely to be protons and nuclei rather than electrons. The energy associated with the cosmic rays could have come from a single supernova explosion around 10 4 years ago.

The detection of fast variations of the tera-electron volt (TeV) (10¹² eV) γ-ray flux, on time scales of days, from the nearby radio galaxy M87 is reported. These variations are about 10 times as fast as those observed in any other wave band and imply a very compact emission region with a dimension similar to the Schwarzschild radius of the central black hole. We thus can exclude several other sites and processes of the γ-ray production. The observations confirm that TeV γ rays are emitted by extragalactic sources other than blazars, where jets are not relativistically beamed toward the observer.

X-ray binaries are composed of a normal star in orbit around a neutron star or stellar-mass black hole. Radio and x-ray observations have led to the presumption that some x-ray binaries called microquasars behave as scaled-down active galactic nuclei. Microquasars have resolved radio emission that is thought to arise from a relativistic outflow akin to active galactic nuclei jets, in which particles can be accelerated to large energies. Very high energy [gamma]-rays produced by the interactions of these particles have been observed from several active galactic nuclei. Using the High Energy Stereoscopic System, we find evidence for gamma-ray emission of >100 gigaelectron volts from a candidate microquasar, LS 5039, showing that particles are also accelerated to very high energies in these systems.

The diffuse extragalactic background light consists of the sum of the starlight emitted by galaxies through the history of the Universe, and it could also have an important contribution from the 'first stars', which may have formed before galaxy formation began. Direct measurements are difficult and not yet conclusive, owing to the large uncertainties caused by the bright foreground emission associated with zodiacal light. An alternative approach is to study the absorption features imprinted on the gamma-ray spectra of distant extragalactic objects by interactions of those photons with the background light photons. Here we report the discovery of gamma-ray emission from the blazars H 2356 -309 and 1ES 1101 -232, at redshifts z = 0.165 and z = 0.186, respectively. Their unexpectedly hard spectra provide an upper limit on the background light at optical/near-infrared wavelengths that appears to be very close to the lower limit given by the integrated light of resolved galaxies. The background flux at these wavelengths accordingly seems to be strongly dominated by the direct starlight from galaxies, thus excluding a large contribution from other sources- in particular from the first stars formed. This result also indicates that intergalactic space is more transparent to gamma-rays than previously thought.

The characterization of flash flood is an opened subject. We can notice several characteristics. The precipitation responsible of their formation are violent and intense; catchments concerned are small, or medium; the surface runoff is the main flood generator; and the infiltration plays a role in the losses evaluation of the rain measured. To simulate and to forecast such events, we use two deterministic, distributed and conceptual models : TOPMODEL and MARINE. MAFUNE is an operational and robust tool for flash flood forecasting already implemented in National Flood Forecast Service in order to be tested. It should supply pertinent data about the flood evolution for people responsible of forecast and should be applicable even for sparse historical

The source of Galactic cosmic rays (with energies up to 1015 eV) remains unclear, although it is widely believed that they originate in the shock waves of expanding supernova remnants. At present the best way to investigate their acceleration and propagation is by observing the gamma-rays produced when cosmic rays interact with interstellar gas. Here we report observations of an extended region of very-high-energy ( 1011 eV) gamma-ray emission correlated spatially with a complex of giant molecular clouds in the central 200 parsecs of the Milky Way. The hardness of the gamma-ray spectrum and the conditions in those molecular clouds indicate that the cosmic rays giving rise to the gamma-rays are likely to be protons and nuclei rather than electrons. The energy associated with the cosmic rays could have come from a single supernova explosion around 104 years ago.[PUBLICATION ABSTRACT]

Subdued lighting The diffuse light permeating intergalactic space contains precious information about the early Universe. Exactly what information is a matter of conjecture: light from the first stars, perhaps, or direct starlight from later galaxies? Gamma-ray observations of two distant active galaxies with HESS, the High Energy Stereoscopic System array in Namibia, reveal that the diffuse light intensity is lower than expected from recent claims. This suggests that the Universe is more transparent to [gamma]-rays than was thought, and favours galaxies as the dominant light source, rather than early stars. The diffuse extragalactic background light consists of the sum of the starlight emitted by galaxies through the history of the Universe, and it could also have an important contribution from the 'first stars', which may have formed before galaxy formation began. Direct measurements are difficult and not yet conclusive, owing to the large uncertainties caused by the bright foreground emission associated with zodiacal light.sup.1. An alternative approach.sup.2,3,4,5 is to study the absorption features imprinted on the [gamma]-ray spectra of distant extragalactic objects by interactions of those photons with the background light photons.sup.6. Here we report the discovery of [gamma]-ray emission from the blazars.sup.7 H 2356 - 309 and 1ES 1101 - 232, at redshifts z = 0.165 and z = 0.186, respectively. Their unexpectedly hard spectra provide an upper limit on the background light at optical/near-infrared wavelengths that appears to be very close to the lower limit given by the integrated light of resolved galaxies.sup.8. The background flux at these wavelengths accordingly seems to be strongly dominated by the direct starlight from galaxies, thus excluding a large contribution from other sources--in particular from the first stars formed.sup.9. This result also indicates that intergalactic space is more transparent to [gamma]-rays than previously thought.

The detection of fast variations of the tera-electron volt (TeV) (10 super(12) eV) {gamma}-ray flux, on time scales of days, from the nearby radio galaxy M87 is reported. These variations are about 10 times as fast as those observed in any other wave band and imply a very compact emission region with a dimension similar to the Schwarzschild radius of the central black hole. We thus can exclude several other sites and processes of the {gamma}-ray production. The observations confirm that TeV {gamma} rays are emitted by extragalactic sources other than blazars, where jets are not relativistically beamed toward the observer.