Phage therapy as an approach to prevent Vibrio anguillarum infections in fish larvae production

Fish larvae in aquaculture have high mortality rates due to pathogenic bacteria, especially the Vibrio species, and ineffective prophylactic strategies. Vaccination is not feasible in larvae and antibiotics have reduced efficacy against multidrug resistant bacteria. A novel approach to controlling Vibrio infections in aquaculture is needed. The potential of phage therapy to combat vibriosis in fish larvae production has not yet been examined. We describe the isolation and characterization of two bacteriophages capable of infecting pathogenic Vibrio and their application to prevent bacterial infection in fish larvae. Two groups of zebrafish larvae were infected with V. anguillarum (∼106 CFU mL-1) and one was later treated with a phage lysate (∼108 PFU mL-1). A third group was only added with phages. A fourth group received neither bacteria nor phages (fish control). Larvae mortality, after 72 h, in the infected and treated group was similar to normal levels and significantly lower than that of the infected but not treated group, indicating that phage treatment was effective. Thus, directly supplying phages to the culture water could be an effective and inexpensive approach toward reducing the negative impact of vibriosis in larviculture

Low-energy 23^{23}Al β\beta-delayed proton decay and 22^{22}Na destruction in novae

International audienceThe radionuclide Na22 is a target of γ-ray astronomy searches, predicted to be produced during thermonuclear runaways driving classical novae. The Na22(p,γ)Mg23 reaction is the main destruction channel of Na22 during a nova, hence, its rate is needed to accurately predict the Na22 yield. However, experimental determinations of the resonance strengths have led to inconsistent results. In this Rapid Communication, we report a measurement of the branching ratios of the Al23β-delayed protons as a probe of the key 204-keV (center-of-mass) Na22(p,γ)Mg23 resonance strength. We report a factor of 5 lower branching ratio compared to the most recent literature value. The variation in Na22 yield due to nuclear data inconsistencies was assessed using a series of hydrodynamic nova outburst simulations and has increased to a factor of 3.8, corresponding to a factor of ≈2 uncertainty in the maximum detectability distance. This is the first reported scientific measurement using the Gaseous Detector with Germanium Tagging system

GADGET: a Gaseous Detector with Germanium Tagging

International audienceThe Gaseous Detector with Germanium Tagging (GADGET) is a new detection system devoted to the measurement of weak, low-energy β -delayed proton decays relevant for nuclear astrophysics studies. It is comprised of a new gaseous Proton Detector equipped with a Micromegas readout for charged particle detection, surrounded by the existing Segmented Germanium Array (SeGA) for the high-resolution detection of the prompt γ -rays. In this work we describe in detail for the first time the design, construction, and operation of the GADGET system, including performance of the Proton Detector. We present the results of a recent commissioning experiment performed with 25 Si beam at the National Superconducting Cyclotron Laboratory (NSCL). GADGET provided low-background, low-energy β -delayed proton detection with efficiency above 95%, and relatively good efficiency for proton-gamma coincidences (2.7% at 1.37 MeV)

25^{25}Si β+\beta^+ -decay spectroscopy

International audienceBackground: β-decay spectroscopy provides valuable information on exotic nuclei and a stringent test for nuclear theories beyond the stability line. Purpose: To search for new β-delayed protons and γ rays of Si25 to investigate the properties of Al25 excited states. Method: Si25β decays were measured by using the Gaseous Detector with Germanium Tagging system at the National Superconducting Cyclotron Laboratory. The protons and γ rays emitted in the decay were detected simultaneously. A Monte Carlo method was used to model the Doppler broadening of Mg24γ-ray lines caused by nuclear recoil from proton emission. Shell-model calculations using two newly developed universal sd-shell Hamiltonians were performed. Results: The most precise Si25 half-life to date has been determined. A new proton branch at 724(4) keV and new proton-γ-ray coincidences have been identified. Three Mg24γ-ray lines and eight Al25γ-ray lines are observed for the first time in Si25 decay. The first measurement of the Si25β-delayed γ-ray intensities through the Al25 unbound states is reported. All the bound states of Al25 are observed to be populated in the β decay of Si25. Several inconsistencies between the previous measurements have been resolved, and new information on the Al25 level scheme is provided. An enhanced decay scheme has been constructed and compared to the mirror decay of Na25 and the shell-model calculations. Conclusions: The measured excitation energies, γ-ray and proton branchings, log ft values, and Gamow-Teller transition strengths for the states of Al25 populated in the β decay of Si25 are in good agreement with the shell-model calculations, offering gratifyingly consistent insights into the fine nuclear structure of Al25