Publications récentes

A Novel Highly Efficient Device for Growing Micro-Aerophilic Microorganisms

Auteurs : Maxime Fuduche (MIO) , Sylvain Davidson (MIO),   Céline Boileau (MIO), Long-Fei Wu and Yannick Combet-Blanc (MIO)

Front. Microbiol., 19 March 2019 | https://doi.org/10.3389/fmicb.2019.00534

Abstract : This work describes a novel, simple and cost-effective culture system, named the Micro-Oxygenated Culture Device (MOCD), designed to grow microorganisms under particularly challenging oxygenation conditions. Two microaerophilic magnetotactic bacteria, a freshwater Magnetospirillum gryphiswaldense strain MSR-1 and a marine Magnetospira sp. strain QH-2, were used as biological models to prove the efficiency of the MOCD and to evaluate its specifications. Using the MOCD, growth rates of MSR-1 and QH-2 increased by four and twofold, respectively, when compared to traditional growing techniques using simple bottles. Oxystat-bioreactors have been typically used and specifically designed to control low dissolved oxygen concentrations, however, the MOCD, which is far less sophisticated was proven to be as efficient for both MSR-1 and QH-2 cultures with regard to growth rate, and even better for MSR-1 when looking at cell yield (70% increase). The MOCD enables a wide range of oxygenation conditions to be studied, including different O2-gradients. This makes it an innovative and ingenious culture device that opens up new parameters for growing microaerobic microorganisms.

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A Glider-Compatible Optical Sensor for the Detection of Polycyclic Aromatic Hydrocarbons in the Marine Environment

Authors : Frédéric Cyr, Marc Tedetti (MIO), Florent Besson, Nagib Bhairy (MIO) and Madeleine Goutx (MIO)

Front. Mar. Sci., 18 March 2019 | https://doi.org/10.3389/fmars.2019.00110

Résumé :

Cette étude présente le MiniFluo-UV, un capteur de fluorescence compatible avec les planeurs océaniques, qui cible la détection des hydrocarbures aromatiques polycycliques (HAP) dans le milieu marin. Deux MiniFluos peuvent être installés sur un planeur, chacun équipé de deux canaux optiques (un HAP est mesuré par canal). Cette configuration permet de mesurer jusqu'à 4 HAP fluorescents différents : le naphtalène, le phénanthrène, le fluorène et le pyrène. Des tests en laboratoire sur les produits pétroliers (pétrole brut et diesel Maya) ainsi que sur des échantillons marins situés à proximité de zones industrielles (ports urbains et installations offshore) ont révélé que la concentration des quatre HAP ciblés représentait entre 62% et 97% de la concentration totale d'HAP détectée en échantillons (HAP P16 déterminés par des protocoles internationaux standard). Les tests de laboratoire ont également révélé que, pour les applications marines, l’étalonnage de la fraction de pétrole brut adaptée à l’eau (WAF) est plus approprié que celui des étalons purs (STD). En effet, la fluorescence des HAP est constituée en grande partie de composés alkylés qui ne sont pas pris en compte avec l’étalonnage STD. Les résultats de trois déploiements de planeurs dans des niveaux de complexité croissants (un essai en laboratoire, une admission sur le terrain en mode non autonome et une mission totalement autonome) sont également présentés. Au cours des déploiements sur le terrain, l’ensemble MiniFluo-planeur « SeaExplorer » a pu détecter des gradients de concentration des eaux marines au large d’un port méditerranéen (<80ngL−1) ainsi que des zones d’hydrocarbures dans les eaux de surface d’un champ d’exploitation pétrolière en Mer du Nord (<200ngL−1, principalement du naphtalène).

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Biochemical composition and energy content of size-fractionated zooplankton east of the Kerguelen Islands

Authors : Mireille Harmelin-Vivien (MIO), Daniela Bӑnaru (MIO) , Charlotte Dromard, Melanie Ourgaud (MIO), François Carlotti
(MIO)

Polar Biology, Springer Verlag, 2019, 42 (3), pp.603-617. 10.1007/s00300-019-02458-8

Abstract :
Food quality is recognized as a key parameter of food web functioning in which zooplankton plays a crucial role not only in linking lower to upper trophic levels but also in transforming the quality of the organic matter available to predators. The influence of size and taxonomic group composition of zooplankton in these processes was assessed in eastern Kerguelen waters (Southern Ocean) at the onset of the spring bloom in 2011. Biochemical (lipids, proteins and carbohydrates) and elemental (carbon and nitrogen) composition were measured in five size—fractions of bulk zooplankton ranging from 80 µm to > 2000 µm and in large copepods, euphausiids, annelids and salps, and energy content was derived from biochemical contents. Proteins were the dominant component of zooplankton dry weight (21.5% dw), followed by lipids (8.9% dw), soluble carbohydrates (2.2% dw) and insoluble carbohydrates (1.0% dw). A concentration increase with zooplankton size for all biochemical components was observed, particularly stronger for proteins and lipids. Copepods and salps provided, respectively, the highest and the lowest amount of lipids and energy.  A four-fold increase in energy content was observed from the smallest to the largest fraction inducing a significant ncrease (> 10 kJ g dw) in the quality of zooplankton matter. This may explain why large zooplankton represent a major food resource for numerous fish, seabirds and marine mammals in the Southern Ocean. Such unique results are required to better quantify energy dynamics in polar food webs.

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Evidence of high N2 fixation rates in the temperate northeast Atlantic

Authors : Debany Fonseca-Batista, Xuefeng Li, Virginie Riou (MIO), Valérie Michotey(MIO), Florian Deman1, François Fripiat5, Sophie Guasco (MIO), Natacha Brion, Nolwenn Lemaitre, Manon Tonnard, Morgane Gallinari6, Hélène Planquette, Frédéric Planchon, Géraldine Sarthou, Marc Elskens, Julie LaRoche, Lei Chou, Frank Dehairs

Biogeosciences, 16, 999–1017, 2019

https://doi.org/10.5194/bg-16-999-2019

Abstract. : Diazotrophic activity and primary production (PP) were investigated along two transects (Belgica BG2014/14 and GEOVIDE cruises) off the western Iberian Margin and the Bay of Biscay in May 2014. We report substantial N2fixation activitiesat 8 of the 10 stations sampled, ranging overallbetween 81 and 384 μmol N m-2d-1(0.7 to 8.2 nmol N L-1d-1),withtwo sites close to the Iberian Margin between 38.8° N and 40.7° N yieldingrates 25reachingup to 1355 and 1533 μmol N m-2d-1(65 and 45 nmol N L-1d-1at surface level, respectively).Although diazotrophic activity was not detected at two northern stations in the central Bay of Biscay, when converted to carbon uptake using Redfield stoichiometry, N2fixation at the eight other sites generally contributed to 1–3% of euphotic layer daily PP, and up to 25% and 23%, respectively at the two most active sites. In the Atlantic Ocean, N2fixation rates exceeding 1000 μmol N m-2d-1have previously only been reported in the temperate and tropical western North 30Atlantic waters having coastal, shelf or mesohaline characteristics, as opposed to the mostly open ocean conditions studied here.At the two sites where N2fixation activity wasthe highest; nifHsequences assigned to theprymnesiophyte-symbiont CandidatusAtelocyanobacterium thalassa (UCYN-A)dominated the nifH sequence pool recovered from DNA samples, whilethe remaining sequences, as for all the ones recovered from the other sites,belonged exclusively to non-cyanobacterialphylotypes. Previous studies in the Iberian Basin have systematically 35reported lower N2fixation rates (from < 0.1 to 140 μmol N m-2d-1), as compared to those found in the presentstudy, and this regardless of whether the bubble-addition method or the dissolution method were applied. Earlier studiesin the Iberian region wereconductedlargely outside the bloom period,unlike the present work which was carried out in spring, yet in all cases the assessment of nifHgene diversity, suggests a predominance of UCYN-A and non-cyanobacterial diazotrophs. We support that the unexpectedly high N2fixation activitiesrecorded at the time of our 40study werepromoted by the availability of phytoplankton-derived organic matter produced during the spring bloom, as evidencedby the significant surface particulate organic carbon concentrations,andby the presence of excess phosphorus signature in surface waters, particularly atthe sites with extreme activities. Our findings stress the need2for a more detailed monitoring of oceanic N2fixation in productive waters of the temperate North Atlantic to better constrain the basin-scale nitrogen input to the ocean inventory

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Bacterial Bioluminescence: Light Emission in Photobacterium phosphoreum Is Not Under Quorum-Sensing Control

Authors : Lisa Tanet, Christian Tamburini, Chloé Baumas, Marc Garel, Gwénola Simon and Laurie Casalot (all MIO)

Frontiers in Microbiology March 2019, Volume 10, Article 365

doi: 10.3389/fmicb.2019.00365

Abstract :Bacterial-bioluminescence regulation is often associated with quorum sensing. Indeed, many studies have been made on this subject and indicate that the expression of the light-emission-involved genes is density dependent. However, most of these studies have concerned two model species, Aliivibrio fischeri and Vibrio campbellii. Very few works have been done on bioluminescence regulation for the other bacterial genera. Yet, according to the large variety of habitats of luminous marine bacteria, it would not be surprising to find different light-regulation systems. In this study, we used Photobacterium phosphoreum ANT-2200, a piezophilic bioluminescent strain isolated from Mediterranean deep-sea waters (2200-m depth). To answer the question of whether or not the bioluminescence of P. phosphoreum ANT-2200 is under quorum-sensing control, we focused on the correlation between growth and light emission through physiological, genomic and, transcriptomic approaches. Unlike A. fischeri and V. campbellii, the light of P. phosphoreum ANT-2200 immediately increases from its initial level. Interestingly, the emitted light increases at much higher rate at the low cell density than it does for higher cell-density values. The expression level of the light-emission-involved genes stays constant all along the exponential growth phase. We also showed that, even when more light is produced, when the strain is cultivated at high hydrostatic pressure, no change in the transcription level of these genes can be detected. Through different experiments and approaches, our results clearly indicate that, under the tested conditions, the genes, directly involved in the bioluminescence in P. phosphoreum ANT-2200, are not controlled at a transcriptomic level. Quite obviously, these results demonstrate that the light emission of the strain is not density dependent, which means not under quorum-sensing control. Through this study, we point out that bacterial-bioluminescence regulation should not, from now on, be always linked with the quorum-sensing control.

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Synthesis review of the Gulf of Gabes (eastern Mediterranean Sea, Tunisia): Morphological, climatic, physical oceanographic, biogeochemical and fisheries features

Auteurs : Béjaoui Béchir , Sana Ben Ismail, Achref Othmani, Olfa Ben Abdallah-Ben Hadj Hamida, Cristèle Chevalier (MIO), Wafa Feki-Sahnoun, Ali Harzallah, Nader Ben Hadj Hamida, Riadh Bouaziz, Salem Dahech, Frédéric Diaz (MIO), Khouthir Tounsi, Cherif Sammari, Marc Pagano (MIO), Malika Bel Hassen

Estuarine, Coastal and Shelf Science, 219, 395-408

DOI : 10.1016/j.ecss.2019.01.006

Highlights

•The coastal morphology of the Gulf of Gabes is characterized by beaches, cliffs and wetlands.
•The climate of the Gulf of Gabes is characterized by temperate and hot subtropical Saharan climate.
•The water circulation and water level are closely associated with tides.
•The Gulf of Gabes is considered as the most productive area in the Mediterranean.

 

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Changes in Bacterioplankton Communities Resulting From Direct and Indirect Interactions With Trace Metal Gradients in an Urbanized Marine Coastal Area

 

Authors : Clément Coclet (MIO), Cédric Garnier (MIO), Gaël Durrieu (MIO), Dario Omanović, Sébastien D’Onofrio (MIO), Christophe Le Poupon (MIO), Jean-Ulrich Mullot, Jean-François Briand and Benjamin Misson (MIO)

Front. Microbiol., 22 February 2019  - https://doi.org/10.3389/fmicb.2019.00257

Abstract : Unraveling the relative importance of both environmental conditions and ecologicalprocesses regulating bacterioplankton communities is a central goal in microbialecology. Marine coastal environments are among the most urbanized areas and as aconsequence experience environmental pressures. The highly anthropized Toulon Bay(France) was considered as a model system to investigate shifts in bacterioplanktoncommunities along natural and anthropogenic physicochemical gradients during a1-month survey. In depth geochemical characterization mainly revealed strong andprogressive Cd, Zn, Cu, and Pb contamination gradients between the entrance ofthe Bay and the north-western anthropized area. On the other hand, low-amplitudenatural gradients were observed for other environmental variables. Using 16S rRNAgene sequencing, we observed strong spatial patterns in bacterioplankton taxonomicand predicted function structure along the chemical contamination gradient. Variationpartitioning analysis demonstrated that multiple metallic contamination explained thelargest part of the spatial biological variations observed, but DOC and salinity werealso significant contributors. Network analysis revealed that biotic interactions were farmore numerous than direct interactions between microbial groups and environmentalvariables. This suggests indirect effects of the environment, and especially trace metals,on the community through a few taxonomic groups. These spatial patterns werealso partially found for predicted bacterioplankton functions, thus indicating a limitedfunctional redundancy. All these results highlight both potential direct influences of tracemetals contamination on coastal bacterioplankton and indirect forcing through bioticinteractions and cascading.

Keywords : coastal ecosystem, metal contamination gradients, bacterioplankton community structure, functional prediction, co-occurrence network

 

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Toward science-oriented validations of coastal altimetry: Application to the Ligurian Sea

 

Authors : M.Meloni, J.Bouffard, A.M.Dogliolic (MIO), A.Petrenko (MIO), G.Valladeaud

Remote Sensing of Environment
Volume 224, April 2019, Pages 275-288 - https://doi.org/10.1016/j.rse.2019.01.028

Abstract : This study is a preliminary contribution to the European Space Agency's efforts aimed at establishing reference in situ networks specifically targeted to validate coastal altimetry. For this purpose, we processed and cross-compared conjointly improved altimetry data and in situ measurements acquired over the Ligurian Sea – a coastal region of the Mediterranean characterised by complex, fine-scale and rapidly evolving oceanic features. We made use of several kinds of multi-sensor in situ observations located along SARAL and Jason-2 tracks. The main objectives of the study were to assess improved coastal oriented validation strategies, including the usage of a new in situ platform (Moving Vessel Profiler), while better understanding potential differences owing to physical content inconsistency and instrumental or data processing limitations. The results show remarkable agreements over spatial scales of few tens of kilometres, paving the way for the deployment of future in situ networks and the definition of science-oriented diagnostics targeted to assess the capability of present and future high-resolution altimetric missions in resolving small-scale physical features.

Keywords : Coastal altimetry Mesoscale Validation and verification Northern current

 

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Pascal Hingamp (MIO) co-auteur de Minimum Information about an Uncultivated Virus Genome (MIUViG)

 

In Nature Biotechnology volume 37, pages 29–37 (2019)

Authors : Roux S, Adriaenssens EM, Dutilh BE, Koonin EV, Kropinski AM, Krupovic M, Kuhn JH, Lavigne R, Brister JR, Varsani A, Amid C, Aziz RK, Bordenstein SR, Bork P, Breitbart M, Cochrane GR, Daly RA, Desnues C, Duhaime MB, Emerson JB, Enault F, Fuhrman JA, Hingamp P (MIO), Hugenholtz P, Hurwitz BL, Ivanova NN, Labonté JM, Lee KB, Malmstrom RR, Martinez-Garcia M, Mizrachi IK, Ogata H, Páez-Espino D, Petit MA, Putonti C, Rattei T, Reyes A, Rodriguez-Valera F, Rosario K, Schriml L, Schulz F, Steward GF, Sullivan MB, Sunagawa S, Suttle CA, Temperton B, Tringe SG, Thurber RV, Webster NS, Whiteson KL, Wilhelm SW, Wommack KE, Woyke T, Wrighton KC, Yilmaz P, Yoshida T, Young MJ, Yutin N, Allen LZ, Kyrpides NC, Eloe-Fadrosh EA.

Abstract : We present an extension of the Minimum Information about any (x) Sequence (MIxS) standard for reporting sequences of uncultivated virus genomes. Minimum Information about an Uncultivated Virus Genome (MIUViG) standards were developed within the Genomic Standards Consortium framework and include virus origin, genome quality, genome annotation, taxonomic classification, biogeographic distribution and in silico host prediction. Community-wide adoption of MIUViG standards, which complement the Minimum Information about a Single Amplified Genome (MISAG) and Metagenome-Assembled Genome (MIMAG) standards for uncultivated bacteria and archaea, will improve the reporting of uncultivated virus genomes in public databases. In turn, this should enable more robust comparative studies and a systematic exploration of the global virosphere.

 

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A Mild-Slope System for Bragg Scattering of Water Waves by Sinusoidal Bathymetry in the Presence of Vertically Sheared Currents

 

Authors : Kostas Belibassakis, Julien Touboul (MIO), Elodie Laffitte (MIO), Vincent Rey (MIO).

Received : 12 October 2018 / Accepted : 29 December 2018 / Published : 7 January 2019
J. Mar. Sci. Eng. 2019, 7(1), 9 ; doi:10.3390/jmse7010009

Abstract : Extended mild-slope models (MMSs) are examined for predicting the characteristics of normally incident waves propagating over sinusoidal bottom topography in the presence of opposing shearing currents. It is shown that MMSs are able to provide quite good predictions in the case of Bragg scattering of waves over rippled bathymetry without a current, but fail to provide good predictions concerning the resonant frequency in the additional presence of a current. In order to resolve the above mismatch, a two-equation mild-slope system (CMS2) is derived from a variational principle based on the representation of the wave potential expressed as a superposition of the forward and backward components. The latter system is compared against experimentally measured data collected in a wave flume and is shown to provide more accurate predictions concerning both the resonant frequency and the amplitude of the reflection coefficient. Future work will be devoted to the examination of the derived model for a more general wave system over realistic seabed topography. View Full-Text

Keywords : wave-current interaction ; sinusoidal bathymetry ; resonant reflection ; mild-slope equation ; coupled-mode system

 

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Damage-related protein turnover explains inter-specific patterns of maintenance rate and suggests modifications of the DEB theory

 

Authors : Olivier Maury, Jean-Christophe Poggiale (MIO), Olivier Aumont

Journal of Sea Research, Elsevier, 2019, 143, pp.35-47

Abstract : Maintenance is the energy that living organisms are bound to use to maintain their structure in a viable state. It includes all the metabolic and physiological costs that are not directly associated to the production of biomass (growth and reproduction) or to development (maturation). In the framework of the DEB theory, somatic maintenance rate can either be proportional to organism structural volume V or, more marginally, to structural surface V 2/3. Being mostly associated to similar metabolic processes, volume specific maintenance costs are not expected to vary substantially at both intra-and interspecific levels. In the DEB theory, the volume-specific maintenance rate is therefore supposed to keep constant from birth to death and to remain approximately constant between species. However, a recent meta-analysis of DEB parameters estimated using the Add-my-Pet collection (Kooijman, 2014) reveals troubling patterns apparently violating this inter-specific scaling rule and challenging the DEB theory. It is indeed shown in this study that empirically-derived volume-specific maintenance rates scale approximately with, and display a very high variability around this trend. Overall, estimated maintenance rates in Add-my-Pet span over three to four orders of magnitude, thus invalidating the assumption of constant maintenance rate between species, which underpins the covariation rules for parameter values of the DEB theory. In an attempt to address this major problem for the DEB theory, we propose a simple physiological mechanism that would simultaneously explain the apparent decrease of volume-specific maintenance rate with ultimate size and its apparent variability for a given range of maximum size. Our proposition consists in making protein (and more generally structure) turnover explicit in maintenance and linking protein damage rate to aerobic metabolism and the production of ROS, which are decreasing with both structural volume and maximum structural volume. We show that this implies that the actual volume specific maintenance rate varies both at the intra- and inter-specific levels in a range very similar to what is observed in the Add-my Pet data estimations. If true, this implies that the apparent decrease of volume-specific maintenance rate with ultimate size is an artefact and it requires modifications of the standard DEB theory in order to capture empirical inter-specific scaling patterns of DEB parameters while keeping the consistency of the theory at both intra- and inter-specific levels.

 

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Spatio-temporal variability in benthic exchanges at the sediment-water interface of a shallow tropical coastal lagoon (south coast of Gulf of Mexico)

 

Authors : Christian Grenz (MIO), Montserrat Moreno (MIO), Karline Soetaert, Lionel Denis, Pascal Douillet (MIO), Renaud Fichez (MIO)

Estuarine, Coastal and Shelf Science
Volume 218, 5 March 2019, Pages 368-380

Abstract : The sediment in Laguna de Términos, the largest and shallowest system in the Southwest portion of the Gulf of Mexico features a broad range of ecological and hydrobiological characteristics driven by annual weather cycles (dry and wet seasons), causing large salinity gradients during the wet season due to large river discharges. Four sampling campaigns were carried out during the wet and the dry seasons in 2009 and 2010 on a selection of 13 out of 35 stations. Measurements of Sediment Oxygen Demand (SOD) and nutrient fluxes at the sediment-water interface were performed using lab incubations with 15 cm diameter sediment cores. SOD fluctuated between 1327 ± 161 and 2248 ± 359 μmol m −2 h −1 for dry and wet seasons respectively. Silicate effluxes were also significantly higher during the wet seasons (89.4 ± 15.9 μmol m −2 h −1) than during the dry season (46.5 ± 11.4 μmol m −2 h −1). PO 4 fluxes were low all over the study period without seasonal trend. No significant difference was measured for DIN fluxes but there was a tendency for DIN uptake during the wet season (−2.9 ± 18.8 μmol m −2 h −1) and conversely an efflux during the dry season (24.3 ± 7.3 μmol m −2 h −1). SOD correlated to organic matter and chloropigment content of the sediments while silicate fluxes responded to enhanced chloropigments in the sediments. During both seasons, total benthic nutrient fluxes overwhelmed largely riverine inputs and benthic carbon mineralization rates approximated a significant proportion of the pelagic organic carbon production. We conclude that benthic processes in Laguna de Términos are largely driven by weather variability and that they contribute substantially to carbon and nutrient budgets in this shallow subtropical system.

 

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