Virus, bactéries et protistes pathogènes du phytoplancton, le rôle insoupçonné des parasites dans le fonctionnement des écosystèmes aquatiques

International audienceMicroscopiques, les parasites sont la plupart du temps invisibles, mais présents partout. Ils infectent tous les organismes du monde vivant. La dernière décennie a révélé une incroyable diversité chez les parasites viraux, bactériens et eucaryotes. Ceux infectant le phytoplancton pourraient avoir une importance capitale dans la dynamique des populations algales et dans le fonctionnement des écosystèmes aquatiques, mais leur rôle est encore très largement méconnu à ce jour (Brussaard, 2004). Sur ces questions, la recherche ne fait que commencer

La Sainte famille

Adopting a diachronic and interdisciplinary approach, this book questions the relationship maintained by the Church and the Catholic world with the family

Distribution des principaux groupes d’eucaryotes de petite taille en milieu marin et lacustre

Marine and freshwater eukaryotic microbial communities are composed of organisms found in all protist lineages known to date. The smaller autotrophs can significantly contribute to both biomass and primary production in oligotrophic waters. Until now, about 100 marine and freshwater species have been formally described in the picoplanktonic size range (< 3 μm). Their distribution and their contribution to chlorophyll biomass begin to be known for some marine species such as the Prasinophyceae Micromonas pusilla. In order to better understand the diversity and ecology of these small eukaryotes, I used fluorescent in situ hybridization of 18S rRNA oligonucleotide probes coupled with signal amplification (TSA-FISH) to quantify specific taxonomic groups in natural samples. In particular, existing probes targeting Chlorophyta and Haptophyta were used in order to evaluate the distribution of these two major groups in different environments. In parallel, epifluorescence microscopy observations on glutaraldehyde fixed samples were achieved to distinguish autotrophic from heterotrophicorganisms. Various marine regions were investigated, exhibiting very different trophic status such as the South-East Pacific, the English Channel and the North Sea. Freshwater samples came from a meso-eutrophic lake in Luxemburg (one year long sampling) and from three French lakes (meso-oligotrophic, mesotrophic and eutrophic). The contribution of heterotrophic part of the eukaryote community reached 75 % for the picosize fraction in the oligotrophic zones of the South-East Pacific and50 % in the Pacific meso and eutrophic zones as well as in the North Sea. The contribution of Chlorophyta among autotrophic eukaryotes reached its maximum in the English Channel within the pico size fraction (up to 100 %) while the Haptophyta contribution was maximal for the size fraction between 2 μm and 5 μm in the North Sea (up to 100 %). Chlorophyta populations were principally composed of Mamiellales for the pico size fraction with adominance of the species Micromonas pusilla in the English Channel. Freshwater samples showed contributions of Chlorophyta and Haptophyta generally lower than in marine samples whatever the trophic status of the lake (from 5 % to 27 % on average for Chlorophyta and from 2 % to 9 % for Haptophyta in summer for the four lakes investigated). While no clear pattern was found for Haptophyta, Chlorophyta contribution for the fraction smaller than 2 μm seemed to decrease in more eutrophic waters. Annual monitoring of the Esch-sur-Sure Lake (Luxemburg) showed that the highest contribution of Chlorophyta (99 %) and Haptophyta (9 %) occurred in the larger than 5 μm fraction during the clear water phase and in autumn, respectively. Clone libraries of the 18S rRNA gene obtained at four seasons in the Esch-sur-Sure Lake tends to confirm the dominance of heterotrophic eukaryotes among the pico population in particular ciliates. In summer, Chlorophyta represented 12 % of the identified phylotypes. The present study confirmed the dominance of the “red lineage” for the larger than 5 μm fraction whatever the environment considered. The “green lineage” dominated the picoplanctonic fraction only in the English Channel and the North Sea. However, during the clear water phase in the Esch-sur-Sûre Lake, it dominated the larger than 5 μm fraction.Les communautés microbiennes eucaryotes sont composées d’organismes faisant partie de toutes les lignées de protistes connues à ce jour. Les autotrophes de petite taille peuvent contribuer de façon significative à la biomasse et à la production primaire dans les eaux oligotrophes. Jusqu’à présent, moins de 80 espèces marines et d’eau douce ont été formellement décrites dans la classe de taille picoplanctonique (< 3 µm). Leur distribution et leur contribution à la biomasse chlorophyllienne commencent à être connues pour quelques espèces marines comme le Prasinophyceae Micromonas pusilla. Dans le but de mieux comprendre la diversité et l’écologie de ces petits eucaryotes, j’ai utilisé l’hybridation in situ fluorescente de sondes oligonucleotidiques (18S ARNr) associées à une amplification du signal (FISH-TSA) afin de quantifier des groupes taxinomiques spécifiques dans des échantillons naturels. En particulier, des sondes déjà existantes spécifiques des Chlorophyta et des Haptophyta ont été utilisées afin d’évaluer les distributions de ces deux grands groupes dans différents environnements. En parallèle, des observations en microscopie à épifluorescence sur des échantillons fixés au glutaraldéhyde ont permis de distinguer les organismes autotrophes des hétérotrophes. Différentes milieux marins caractérisés par des statuts trophiques différents ont été étudiés, tels que le Pacifique Sud-Est, la Manche et la Mer du Nord. Des échantillons d’eau douce provenant d’un lac méso-eutrophe au Luxembourg (une année d’échantillonnage) et de trois lacs français (méso-oligotrophe, mésotrophe et eutrophe) ont été également étudiés. La contribution hétérotrophe de la communauté eucaryotique atteignait 75 % de la population picoplanctonique dans les zones oligotrophes du Pacifique Sud-Est et 50 % dans les zones mésotrophes et eutrophes du Pacifique et de Mer du Nord. La contribution des Chlorophyta parmi les eucaryotes autotrophes atteignait son maximum dans la Manche au niveau de la fraction picoplanctonique (jusqu’à 100 %) alors que les Haptophyta avaient une contribution maximale dans la fraction de taille entre 2 µm et 5 µm en Mer du Nord (jusqu’à 100 %). Les Chlorophyta étaient principalement composés de Mamiellales pour la fraction picoplanctonique avec une dominance de l’espèce Micromonas pusilla dans la Manche. Les échantillons d’eau douce ont montré des contributions des Chlorophyta et des Haptophyta généralement plus basses que les échantillons marins et ce quelque soit le statut trophique du lac (de 5 % à 27 % en moyenne pour les Chlorophyta et de 2 % à 9 % pour les Haptophyta en été pour les quatre lacs étudiés). Alors qu’aucune tendance claire n’a pas été mise en évidence pour les Haptophyta, la contribution des Chlorophyta dans la fraction inférieure à 2 µm semble décroître dans les eaux plus eutrophes. L’étude annuelle du lac d’Esch-sur-Sûre (Luxembourg) a montré que la plus importante contribution des Chlorophyta (99 %) et des Haptophyta (9 %) est atteinte pour la fraction supérieure à 5 µm durant la phase d’eau claire et en automne, respectivement. Les banques de clones (18S ARNr) réalisées aux quatre saisons au lac d’Esch-sur-Sûre tendent à confirmer la dominance des eucaryotes hétérotrophes parmi la population picoplanctonique, en particulier les ciliés. En été, les Chlorophyta représentaient 12 % des phylotypes identifiés. Cette étude a confirmé la dominance de la « lignée rouge » dans la fraction supérieure à 5 µm en été quelque soit le milieu considéré. La « lignée verte » dominait la fraction picoplanctonique uniquement en Manche et en Mer du Nord. Cependant, durant la phase d’eau claire dans le lac d’Esch-sur-Sûre, elle dominait également la fraction supérieure à 5 µm

Mycorrhizal industry in modern agriculture

SPE IPMInternational audienc

Advances in in vitro culture of AM fungi

National audienceIn vitro inoculum production of arbuscular mycorrhizal (AM) fungi has several advantages over traditional systems. In particular, it allows an important production of contaminant-free fungal propagules in a short time, and it is more economical. Therefore, our goal is to develop in vitro inoculum production of AM fungi of interest. This goal has been achieved with a Glomus sp. originating from Symbiom, Czech Republic. Until now, the molecular characterization on mitochondrial and nuclear DNA has not permitted to distinguish this isolate from Glomus irregulare (Syn. Rhizophagus irregularis; DAOM197198). However, the Glomus sp. isolate presents morphological (white drop-shape spores) and physiological (faster growth) characteristics different from those of DAOM197198, and new molecular approach should be developed to distinguish it

Conception and Development of Recycled Raw Materials (Coconut Fiber and Bagasse)-Based Substrates Enriched with Soil Microorganisms (Arbuscular Mycorrhizal Fungi, Trichoderma spp. and Pseudomonas spp.) for the Soilless Cultivation of Tomato (S. lycopersicum)

The global production quantity and the utilisation area harvested for the cultivation of tomatoes have significantly increased in the last three decades. Europe still plays an important role in the production of tomatoes, accounting for 12% of global production in 2020. Tomato production can be divided into greenhouse/soilless production and open field production. Greenhouse/soilless tomato production is mostly developed in northern Europe, and open field production in southern Europe. Soilless cultivation serves to improve control of the growing medium and to avoid any likely problems for watering and maintaining proper nutrient concentrations. Beneficial soil microorganisms, particularly arbuscular mycorrhizal fungi (AMF), are increasingly being recognized as key elements of an agro-ecological approach to agricultural production. The use of these beneficial microorganisms on soilless tomato production may improve plant performance and reduce biotic and abiotic stress occurring during production with a consequent decrease of chemicals and increase of sustainability of the production system. In this paper, we tested different substrates composed of coconut fiber and bagasse (S1 to S4) and beneficial microorganisms (AMF, Pseudomonas fluorescens and Trichoderma harzianum), selecting the most suitable system for the soilless production of tomatoes. Our results showed that substrates S1 (100% coconut fiber) and S2 (66% coconut fiber + 33% bagasse) complementarily used with the consortium of &ldquo;AMF IP21 + Trichoderma harzianum + Pseudomonas fluorescens IPB04&rdquo; seem to be the &ldquo;best formulation&rdquo; for this purpose. That confirmed the feasibility of the development of recycled material (coconut fiber and bagasse)-based substrates together with soil microorganisms (AMF and beneficial bacteria) for soilless tomato production

Conception and Development of Recycled Raw Materials (Coconut Fiber and Bagasse)-Based Substrates Enriched with Soil Microorganisms (Arbuscular Mycorrhizal Fungi, <i>Trichoderma</i> spp. and <i>Pseudomonas</i> spp.) for the Soilless Cultivation of Tomato (<i>S. lycopersicum</i>)

The global production quantity and the utilisation area harvested for the cultivation of tomatoes have significantly increased in the last three decades. Europe still plays an important role in the production of tomatoes, accounting for 12% of global production in 2020. Tomato production can be divided into greenhouse/soilless production and open field production. Greenhouse/soilless tomato production is mostly developed in northern Europe, and open field production in southern Europe. Soilless cultivation serves to improve control of the growing medium and to avoid any likely problems for watering and maintaining proper nutrient concentrations. Beneficial soil microorganisms, particularly arbuscular mycorrhizal fungi (AMF), are increasingly being recognized as key elements of an agro-ecological approach to agricultural production. The use of these beneficial microorganisms on soilless tomato production may improve plant performance and reduce biotic and abiotic stress occurring during production with a consequent decrease of chemicals and increase of sustainability of the production system. In this paper, we tested different substrates composed of coconut fiber and bagasse (S1 to S4) and beneficial microorganisms (AMF, Pseudomonas fluorescens and Trichoderma harzianum), selecting the most suitable system for the soilless production of tomatoes. Our results showed that substrates S1 (100% coconut fiber) and S2 (66% coconut fiber + 33% bagasse) complementarily used with the consortium of “AMF IP21 + Trichoderma harzianum + Pseudomonas fluorescens IPB04” seem to be the “best formulation” for this purpose. That confirmed the feasibility of the development of recycled material (coconut fiber and bagasse)-based substrates together with soil microorganisms (AMF and beneficial bacteria) for soilless tomato production

Reversible Fe exsolution in the honeycomb Ba(Fe,M)2-x(PO4)2 (x<2/3 ; M=Co, Ni) compounds : crystal chemistry, properties and Perspectives

International audienc

Metal exsolution in Ba(Fe,M)2(PO4)2 (M=Li, Co, Ni): Metal versus alkali cationic mobility

International audienc

Human Immunodeficiency Virus Type 1 Genotypic and Pharmacokinetic Determinants of the Virological Response to Lopinavir-Ritonavir-Containing Therapy in Protease Inhibitor-Experienced Patients

The response to regimens including lopinavir-ritonavir (LPV/r) in patients who have received multiple protease (PR) inhibitors (PI) can be analyzed in terms of human immunodeficiency virus type 1 (HIV-1) genotypic and pharmacokinetic (pK) determinants. We studied these factors and the evolution of HIV-1 resistance in response to LPV/r in a prospective study of patients receiving LPV/r under a temporary authorization in Bordeaux, France. HIV-1 PR and reverse transcriptase sequences were determined at baseline LPV/r for all the patients and at month 3 (M3) and M6 in the absence of response to treatment. pK measurements were determined at M1 and M3. Virological failure (VF) was defined as a plasma viral load ≥400 copies/ml at M3. A multivariate analysis of the predictors of VF, including clinical and biological characteristics and the treatment history of the patients, was performed. The PR gene sequence at M0, including individual mutations or a previously defined LPV mutation score (D. J. Kempf, J. D. Isaacson, M. S. King, S. C. Brun, Y. Xu, K. Real, B. M. Bernstein, A. J. Japour, E. Sun, and R. A. Rode, J. Virol. 75:7262-7269, 2001), and the individual exposure to LPV were also included covariates. Sixty-eight patients were enrolled. Thirty-four percent had a virological response at M3. An LPV mutation score of >5 mutations, the presence of the PR I54V mutation at baseline, a high number of previous PIs, prior therapy with ritonavir or indinavir, absence of coprescription of efavirenz, and a lower exposure to LPV or lower LPV trough concentrations were independently associated with VF on LPV/r. Additional PI resistance mutations, including primary mutation I50V, could be selected in patients failing on LPV/r. Genotypic and pK parameters should be used to optimize the virological response to LPV/r in PI-experienced patients and to avoid further viral evolution