Symbiotic bacteria at the origin of magnetoreception in a microorganism
A team of researchers primarily from the Biam1 (CEA-CNRS-Université Aix-Marseille) and the IRSN has discovered symbiotic behavior between magnetotactic bacteria and eukaryotic microorganisms2. This study, published in Nature Microbiology
in late April, opens up new possibilities to understand the mechanisms
involved in the cooperation of senses. Magali Floriani of the IRSN
Laboratory for Radionuclide Ecotoxicology (LECO) conducted some of the
observations under the transmission electron microscope (TEM) of
magnetic bacteria and microorganisms.
allows organisms to orient themselves and navigate along geomagnetic
field lines. The cellular and biophysical processes involved in this
function are fairly well understood in certain prokaryotic
microorganisms but much less so in eukaryotes. In magnetotactic bacteria
(MTB), magnetoreception is ensured by biomineralized ferromagnetic
crystals in microcompartments called magnetosomes. Magnetoreception
works with a chemotactic system to define magnetotaxis, which
facilitates the movement of bacteria towards areas of optimal growth.
researchers found eukaryotic microorganisms with the same magnetotactic
behavior as MTBs in marine sediments. Using microscopy and genomic
approaches, they showed that these organisms live in symbiosis with
non-flagellated magnetic bacteria covering the entire host surface,
forming an assemblage called a holobionte3. The alignment of
bacteria and their chain of magnetosomes along the mobility axis of the
eukaryotic cell allows the microholobiont to orient itself. The
long-lasting, mutual interaction of the partners relies on dual
cooperation involving not only joint magnetotaxis but also metabolic
exchanges. It depends in particular on the exchange of molecular
hydrogen produced by the protist organelles (hydrogenosomes), which
serve as an energy source for ectosymbiotic bacteria4.
work on magnetotactic symbioses not only advances our vision of the
diversity of organisms sensitive to the geomagnetic field but also
expands our knowledge of the ecological strategies involved in the
adaptation of microorganisms to their environment. The researchers would
now like to develop this field of research to better understand the
functional and evolutionary mechanisms involved in the cooperation of
the senses of interacting species and its role in their adaptation to
1. Biosciences and Biotechnologies Institute of Aix-Marseille
2. Refers to all unicellular or
multicellular organisms whose cells are called "eukaryotic." They are
distinguished from prokaryotes by the presence of a nucleus. 3.
Association of a plant or animal host with its hosted microorganisms
(bacteria, archaea, microeukaryotes, and viruses).
4. Symbiosis in which symbiotes live on the surface of their host (and not inside: endosymbiosis)
See the publication
Find out more about Laboratory for Radionuclide Ecotoxicology (LECO)
IRSN doctoral students win lots of awards!
This is a good time for IRSN doctoral students, whether they
are just starting their thesis or recently defended it. On May 29, one
of these students received one of the annual thesis prizes awarded by
the PHENIICS Doctoral School. Two other doctoral students also received
awards in recent weeks.
Beaumont, who defended her thesis conducted at the IRSN last September,
received one of the five prizes (worth 1,000 euros) awarded by the
PHENIICS Doctoral School during the
held on May 29 in Orsay. This award recognizes her work on the 3D
printing calibration phantoms dedicated to personalized internal
dosimetry measurements. During her thesis work, the doctoral student
used graphics software to design age-specific (5, 10, and 15 years)
thyroid phantoms. The primary goal was to improve health risk
assessments in children during a nuclear incident, more specifically
measurements of radionuclide emissions incorporated by the thyroid (i.e.
anthroporadiometric measurements). Measuring instruments were
previously calibrated with adult thyroid phantoms, which therefore did
not take into account the small size of children's thyroid. The phantom
models developed by Tiffany Beaumont have been validated and patented
Benjamin Blaisot, a doctoral student in his third thesis year at the
IRSN Aerosol Physics and Metrology Laboratory (LPMA), received the Best Student Paper award at
27th International Conference on Nuclear Engineering held in Tsukuba,
Japan, from May 19 to 24. His award-winning presentation, "Flash boiling
characterization during ingress coolant event for dust issue in ITER,"
focused on his thesis work on dust issues in the
Benjamin Blaisot is investigating the suspension of dust in the Tokamak
during an ICE (Ingress of Coolant Event) in which water from the
ruptured cooling system is suddenly injected into the ITER torus
initially under vacuum. His work contributes to the knowledge necessary
for proper assessment of contamination source terms, i.e. the quantities
of particles likely to be released into the environment in the event of
an incident involving loss of containment of the ITER torus.
Noémie Guirandy, a doctoral student in her first thesis year at the
IRSN Laboratory for Radionuclide Ecotoxicology (LECO), received one of two poster prizes awarded at the 26th annual conference for doctoral students of the
Doctoral School of Environmental Sciences (ED 251)
held on April 29 and 30 at Aix-Marseille University. Her poster
summarized her initial work on the adverse effects on reprotoxicity and
progeny of chronic gamma irradiation in
Danio rerio fish model.
Find out more about Tiffany Beaumont's thesis
Find out more about Benjamin Blaisot's thesis
Find out more about Noémie Guirandy's thesis (pending)
Facilities - Airborne contamination
DIÈSE, a new facility to analyze particle deposition in a full-scale ventilation system
new facility called DIÈSE(1), dedicated to studying particle transfer
in a full-scale ventilation system, has just been commissioned on the
IRSN Saclay site.
Designed by the Research and Modelling
Laboratory for Airborne Dispersion and Containment (LEMAC), it aims to
study particle deposition (PM2.5, PM10) in ventilation systems, taking
into account geometric discontinuities such as bends, fire dampers,
valves, duct reductions, junctions, etc. The location and quantification
of particle depositions in ventilation system ducts in nuclear
facilities are required in order to characterize contamination transfers
and improve assessment of potential releases under degraded operating
conditions. The facility is the largest of its kind (industrial scale,
with 60 m of 400 x 600 m ducts) and uniquely modular, and it is fitted
with laboratory measurement equipment (PIV(2) laser measurements,
specific particle characterization and deposition measurements).
Schematic diagram of the DIÈSE facility and its modules © IRSN
The DIÈSE facility will be used to produce a multi-year research
program called DÉPART (DÉpot de PARTicules, Particle Deposition), which
aims to validate and develop models for particle deposition in
ventilation systems, implemented using SYLVIA software(3) and CFD
(Computational Fluid Dynamics) simulation software developed or used at
IRSN. The models currently available in this software were developed on
the basis of experiments carried out in small-diameter ducts of
cylindrical cross-section, and the relevance of their use at an
industrial scale and for rectangular cross-sections must be verified.
This extrapolation from scale models will therefore receive experimental
validation by using measurement techniques to analyze turbulences
contributing to aerosol deposition. The first tests within the DÉPART
program are scheduled for early 2020, after the DIÈSE facility
Views of the DIÈSE bench (LD: straight line, CD: bend).
Click on the images to enlarge them
Dépot dans les installations, les équipments et les sondes d’échantillonage, Depositions in facilities, equipment and sampling probes.
(2) Particle Image Velocimetry
Système de logiciels pour l’étude de ventilation, de l’incendie et de l’aérocontamination, Software system to study ventilation, fire and airborne contamination
Find out more about LEMAC
Link to the poster (in French)
Contact: Jeanne Malet
Hydrogen risk: MITHYGENE project extended for a further three years
The MITHYGENE project, which aims to improve our
understanding of how to manage the hydrogen risk – i.e. the risk that
the hydrogen produced during a PWR core meltdown may explode - has been
extended for a further three years, up to 2021. This industrial phase
gathers researchers and engineers from IRSN, CEA-LIST and Arcys.
project has been extended in order to move on from the lab prototype
developed during the second phase (2016-2018) to producing the first
industrial measurement prototype. This system will provide real-time
information on the composition of the atmosphere inside the reactor
containment, and particularly on the concentrations of hydrogen in the
reactor containment, during severe accident conditions.
Launched by IRSN in early October 2013 and funded under France's
'Investment in the Future' program
MITHYGENE is focused on improving our understanding of the phenomena
governing the hydrogen risk and on developing prototype instrumentation
for measuring gas concentrations suitable for use under the conditions
produced in the reactor containment during a severe accident. Advances
made on the project are being used to improve severe accident management
procedures and will also be used in explaining the events that occurred
during the accident at Fukushima-Daiichi in 2011. The findings of the
project should also help improve the practices adopted by industry
operators to eliminate the risk of hydrogen explosion at their own
facilities, be they nuclear or non-nuclear.
objectives of the first two phases in the MITHYGENE project were to
improve the predictability of computer codes used to assess the risk of
hydrogen explosion and to develop real-time in situ instrumentation for
measuring gases, qualified for severe accident conditions. That involved
performing experimental research on hydrogen distribution in the
containment as well as on hydrogen flame propagation and the resistance
of reactor structures and systems to withstand hydrogen gas combustion.
The results obtained have proven pertinent in explaining the sequence of
accidents that occurred at Fukushima-Daiichi. These results are now
being used to plan industrialization of the prototype, the reason for
this extension, which has just recently been launched.
Find out more about MITHYGENE project
IRSN's theses days 2019
theses days 2019 will start on Monday, April 1st until Thursday, April
4th and will take place in La Grande-Motte (France). This seminar, which
takes place every year, is a unique event for the IRSN PhD students to
exchange and meet.
Theses days allow 2nd and 3rd years PhD students to present their
work in front of their colleagues from the institute and from different
research organizations (universities, industries…). The 1st year PhD
students will present their thesis work through poster sessions. During
theses days, for the first time, one of these PhD students will be
rewarded for its poster.
year, the third IRSN's "3 minutes thesis" contest will be held: 12 PhD
students will present their thesis projects in 3 minutes each, in the
clearest and most attractive way possible. The last contest has taken
place in 2017 and was won by Sabine Hoffmann, for her presentation
"Incertitude d'exposition dans les études épidémiologiques" (Uncertainty of exposure in epidemiological studies).
Find out more about theses at IRSNFind out more about IRSN's 3 minutes thesis" contest (in French)
Postdoctoral scholar Nagore Grijalba awarded at the EWCPS 2019
Nagore Grijalba, a postdoctoral scholar at IRSN’s
Radiochemistry, Speciation and Imaging Laboratory (LRSI), won an award
for the poster that she presented at the 18th European Winter Conference on Plasma Spectrochemistry (EWCPS 2019), which took place on February 3-8, 2019 in Pau.
postdoctoral scholar received the Poster Prize of Innovative Analytical
Research for her poster on the “Development of a new methodology for
mapping and quantifying uranium in the kidney using laser ablation
inductively coupled plasma mass spectrometry (LA-ICP-MS)”. More than 300
posters were in the running.
work, which started in summer 2018 for 18 months, aims to develop a
method for analyzing the distribution of uranium in the kidney using a
technique that combines laser ablation with inductively coupled plasma
mass spectrometry (ICP-MS) 1. Very few studies have been
published to date on the use of this technique for the
micro-quantification of uranium in renal tissue. The results were compared with those already obtained using secondary ion mass spectrometry (SIMS) 2 in order to evaluate the performance of each technique with regard to sensitivity and lateral resolution.
The research is
carried out in the LRSI, which has been working for several years on the
micro-distribution of uranium in biological tissue. The lab has
developed a type of analysis based on the SIMS technique to
“micro-locate” the sites where stable or radioactive elements accumulate
in the tissue. This type of analysis has shown that, after chronic
contamination by ingestion, uranium is most likely to accumulate in the
renal cortex and in cell nuclei. The technique cannot, however, be used
to quantify uranium in affected kidney substructures, such as the
proximal convoluted tubules. The work of Nagore Grijalba as part of the
Uranium Kidney CANcer (UKCAN) project, co-funded by Orano, should
provide essential additional information on the micro-location and
micro-quantification of uranium at the renal tissue level in rodents.
In cooperation with IRSN’s
Experimental Radiotoxicology and Radiobiology Laboratory (LRTOX),
these developments should make it possible to establish a correlation
between the distribution of uranium and the biological effects observed
in order to improve knowledge of the mechanisms that prefigure the renal
toxicity of uranium. Furthermore, the data obtained on the location and
quantification of uranium at the renal tissue level should make it
possible to quantify the radiological dose as realistically as possible,
not for the kidney as a whole but for the affected kidney structure, in
association with IRSN’s
Internal Dose Assessment Laboratory (LEDI).
Inductively coupled plasma mass
spectrometry, or ICP-MS, is a type of mass spectrometry capable of
detecting very low concentrations of metals and several non-metals.
Secondary ion mass spectrometry,
or SIMS, is a surface analysis method that consists in bombarding the
surface of the sample to be analyzed with an ion beam.
Photo: Nagore Grijalba during EWCPS 2019. © IRSN
Find out more about the Radiochemistry, Speciation and ImagingLaboratory (LRSI)
The 18th issue of Aktis, IRSN’s scientific newsletter, is available
English-language issue of Aktis, the quarterly newsletter on IRSN’s
research, is available on a HTML and PDF package. Aktis is published
only in a digital version and available in HTML or text format for
e-mail, RSS and pageflip PDF.
this issue, focus on aging the concrete in geological disposal of
radioactive waste. Aktis n°18 also treats of an analysis of the
Fukushima Daiichi accident for IRSN's simulation tools. As well, it
deals with assessment of alpha therapy doses.
The subscription for the English and French versions is complimentary. To read this issue or subscribe, go to
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