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Ciliates represent a diversified group of protists known to establish symbioses with prokaryotic micro-organisms. They are mainly phagotrophs and symbiotic relationships with bacteria can give them an important advantage in chemosynthetic environments. The aim of this study is to describe the thiotrophic association that occurs between the peritrich ciliate Pseudovorticella sp. and potential sulfur-oxidizing bacteria. Investigations at microscopic scale (LM, SEM, TEM) showed ectosymbiotic bacteria covering the surface of the body of Pseudovorticella sp. According to 16S rDNA phylogenetic analysis, these ectosymbiotic bacteria belong to γ-proteobacteria and are phylogenetically close to the symbiont of the recently described Zoothamnium ignavum, which inhabits shallow-water wood falls. FISH experiments, using symbiont specific probes, clearly indicate that these ectosymbiotic bacteria are also ingested into food vacuoles. Electron lucent granules observed in TEM in the cytoplasm of the ectosymbiotic bacteria have been identified as sulfur granules by Raman microspectrometry analyses. Raman microspectrometry analyses confirmed the thiotrophic nature of this relationship already suggested by the results obtained by TEM and phylogeny. A complete sulfur map was then performed to investigate the sulfur distribution in the zooid. Results show that the relationship between this protist and its bacterial partner is a thiotrophic ectosymbiosis.

International audienceThe tribologic properties of graphitized carbon blacks and their fluorinated derivatives are investigated as a function of the fluorination rate. Very low intrinsic friction coefficients are obtained for highly fluorinated compounds. The correlation of the tribologic results and structural investigations of the initial compounds by TEM strongly suggests that the friction mechanisms involve surface effects in the early stage of friction. Long-term tribologic experiments and Raman analyses point out an evolution of the structure and composition of the tribofilms during the friction process leading to similar friction properties of the tribofilms. Wear studies revealed that highly fluorinated derivatives appear less efficient than pristine and weakly fluorinated compounds

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The tribological properties of nanoparticles used as solid lubricants were recently shown [1] to not only depend on their morphology, structure and chemical composition but also on their individual behavior -at the nanoscale -in the sliding interface. In this presentation, we will show the results of in situ experiments performed in the transmission electron microscope (TEM) using a specimen holder fitted with an atomic force microscope (AFM) cantilever. The samples used were small aggregates of carbon nanoparticles and partially fluorinated derivatives. Images were recorded and quantitative data extracted in order to determine their nano-mechanical and tribologic behavior when submitted to compressive and shear stresses.The graphitized carbon black aggregates were purchased from Carbon Superior Graphite (Pureblack ® 205-110). The fluorinated carbon blacks (fluor to carbon atomic ratio: 0.16) were prepared at the Institut de Chimie de Clermont-Ferrand (France). They were obtained by the direct fluorination in a Monel reactor under F 2 atmosphere at 360°C for 3 hours. More details can be found elsewhere [2]. The materials were examined using a high resolution TEM (HRTEM, JEOL JEM-2200FS, operated at 200 kV and equipped with an in column Omega energy filter). The in situ experiments were carried out using a Nanofactory Instruments Inc. specimen holder.The first series of experiments were concerned with the aggregate brittleness induced by the fluorination process. The aggregates were composed of individual spherical particles (diameters of about 10 to 70 nm) with sizes in the range of several tens of nanometers to several micrometers. The fluorination process leads to the formation of an external fluorinated layer (less than 10 nm thick) and may increase the brittleness of the aggregates. They showed remarkable stability during the in situ nano-tribology experiments and the particles remained strongly bonded to each others. Individual aggregates behaved elastically when relatively large compressive stresses were applied. Figure 1 shows three TEM images recorded from a single aggregate before, while and after compression with the AFM tip. The aggregates undergo large deformations without significant damages and the deformation is elastic.The second series of experiments were concerned with the quantitative measurement of the static friction coefficient between the AFM tip and the aggregates of pure graphitized carbon blacks. In that case, a thin silicon cantilever was soldered (using the focused ion beam) onto a support grid normal to the friction direction (a micrograph is shown in Figure 2). The carbon nanoparticles were deposited on the tip of this cantilever and were submitted to normal loads by the AFM tip, in situ. When lateral forces 1500