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International audience; Membrane-bound extracellular vesicles (EVs) are secreted by cells from all three domains of life and their implication in various biological processes is increasingly recognized. In this review, we summarize the current knowledge on archaeal EVs and nanotubes, and emphasize their biological significance. In archaea, the EVs and nanopods have been largely studied in representative species from the phyla Crenarchaeota and Euryarchaeaota. The archaeal EVs have been linked to several physiological processes such as detoxification, biomineralization and transport of biological molecules, including chromosomal, viral or plasmid DNA, thereby taking part in genome evolution and adaptation through horizontal gene transfer. The biological significance of archaeal nanotubes is yet to be demonstrated, although they could participate in EVs biogenesis or exchange of cellular contents. We also discuss the biological mechanisms leading to EV/nanotube biogenesis in Archaea. It has been recently demonstrated that, similar to eukaryotes, EV budding in crenarchaea depends on the ESCRT machinery, whereas the mechanism of EV budding in euryarchaeal lineages, which lack the ESCRT-III homologs, remains unclear.

International audience; Thermococcus gammatolerans EJ3 is an extremophile archaeon which was revealed as one of the most radioresistant organisms known on Earth, withstanding up to 30 kGy gamma-ray radiations. While its theoretical proteome is rather small, T. gammatolerans may enhance its toolbox by post-translational modification of its proteins. Here, we explored its extent of Nε-acetylation of lysines. For this, we immunopurified with two acetylated-lysine antibodies the acetylated peptides resulting from a proteolysis of soluble proteins with trypsin. The comparison of acetylated proteomes of two archaea highlights some common acetylation patterns but only 4 out of 26 orthologous proteins found to be acetylated in both species, are acetylated on the same lysine site. We evidenced that histone B is acetylated in T. gammatolerans at least at two different sites (K27 and K36), and a peptide common at the C-terminus of histones A and B is also acetylated. We verified that acetylation of histones is a common trait among Thermococcales after recording data on Thermococcus kodakaraensis histones and identifying three acetylated sites. This discovery reinforces the strong evolutionary link between Archaea and Eukaryotes and should be an incentive for further investigation on the extent and role of acetylation of histones in Archaea. SIGNIFICANCE: Acetylation is an important post-translational modification of proteins that has been extensively described in Eukaryotes, and more recently in Bacteria. Here, we report for the first time ever that histones in Archaea are also modified by acetylation after a systematic survey of acetylated peptides in Thermococcus gammatolerans. Structural models of histones A and B indicates that acetylation of the identified modified residues may play an important role in histone assembly and/or interaction with DNA. The in-depth protein acetylome landscape in T. gammatolerans includes at least 181 unique protein sequences, some of them being modified on numerous residues. Proteins involved in metabolic processes, information storage and processing mechanisms are over-represented categories in this dataset, highlighting the ancient role of this protein post-translational modification in primitive cells.

International audience; A novel hyperthermophilic, anaerobic archaeon, strain Bio-pl-0405IT2(T), was isolated from an hydrothermal chimney sample collected from the East Pacific Rise at 2700 m depth on the "Sarah Spring" area (7°25'24 S, 107°47'66 W). Cells were irregular, motile cocci (0.8 to 1.5 µm in diameter) and divided by constriction. Growth was observed at temperatures between 60°C and 95°C with an optimum at 80°C. The pH range for growth was between 4 and 8 with an optimum around 7. Strain Bio-pl-0405IT2(T) grew at salt concentrations ranging from 1% to 5% (w/v) NaCl with an optimum at 2%. The novel isolate grew by fermentation or sulphur respiration on a variety of organic compounds. It was a chemoorganoheterotrophic archaeon growing preferentially with yeast extract, peptone and tryptone as carbon and energy sources and sulphur and organic compounds as electron acceptor; it grew also on maltose and starch. Sulphur or L-cystine were required for growth and were reduced to hydrogen sulfide. The strain was resistant to 100 µg/ml rifampicin, chloramphenicol, vancomycin and kanamycin but was sensitive to tetracyclin. The G+C content of its genomic DNA was 53.6 mol%. Phylogenetic analysis of the almost complete 16S rRNA gene sequence (1450 bp) of strain Bio-pl-0405IT2(T) showed that the novel isolate belonged to the genus Thermococcus. The DNA-DNA hybridization values with the two closest relatives T. hydrothermalis and T. celer were below the threshold value of 70%. On the basis of the physiological and genotypic distinctness, we propose a novel species Thermococcus prieurii sp. nov. The type strain is Bio-pl-0405IT2(T) (=CSURP577(T) =JCM16307(T) = LMM3069(T)).