Symbiotic bacteria at the origin of magnetoreception in a microorganism

2019/06/19

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.

Magnetoreception 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.

The 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.

This 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 anoxic environments.

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!

2019/06/17

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.

Tiffany 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 PHENIICS Fest 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 (FR1650855).

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 ICONE27, the 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 ITER Tokamak. 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)

DIÈSE, a new facility to analyze particle deposition in a full-scale ventilation system

2019/05/27
A 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).

 

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 qualification tests.

Views of the DIÈSE bench (LD: straight line, CD: bend). Click on the images to enlarge them

© IRSN

(1) Dépot dans les installations, les équipments et les sondes d’échantillonage, Depositions in facilities, equipment and sampling probes.

(2) Particle Image Velocimetry

(3) 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

Find out more about MITHYGENE project

IRSN's theses days 2019

2019/03/22

IRSN's 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.

This 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).

Postdoctoral scholar Nagore Grijalba awarded at the EWCPS 2019

2019/03/12

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 18^th European Winter Conference on Plasma Spectrochemistry (EWCPS 2019), which took place on February 3-8, 2019 in Pau.

The 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.

Her postdoctoral 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).

1. 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.

2. 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.

The eighteen 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.

In 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 www.irsn.fr/aktis-EN​​.

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