169 research outputs found
Archaeomagnetic results on three Early Iron Age salt-kilns from Moyenvic (France)
International audienceVariations of the EarthÂfs magnetic field during the first millennium BC in western Europe remain poorly constrained, especially archaeointensity changes. Three salt-kilns (MOA, MOB and MOC) sampled in Moyenvic (Lorraine, eastern France) have been studied to provide new reference data. Each kiln has been dated by radiocarbon to originate from the Early Iron Age or Hallstatt period (between VIII and Vth Century BC). Rock magnetic experiments and hysteresis results suggest the predominance of pseudo-single domain (PSD) Ti-poor magnetite. Archaeomagnetic directions obtained by thermal and alternating field demagnetizations have high mean inclination (close to 70.) and declination (between 19 and 31.). A first set of classical Thellier.Thellier experiments was conducted on 46 samples with a laboratory field almost parallel to the direction of the characteristic remanent magnetization (ChRM). Only 24 of these specimens present a linear NRM.TRM plot. For other specimens, NRM.TRM plots are concave-up with positive pTRM checks. The very large dispersion observed between the determined palaeointensity values suggests some artefacts have not been fully recognized. A second set of Thellier experiments was conducted on 34 sister specimens with the laboratory field applied quasi-perpendicular to the ChRM. In these cases,mineralogical evolutions during heating and chemical remanent magnetization acquisitions have been clearly recognized, despite positive pTRM checks. The concave-up shapes of NRM.TRM plots appear mainly due to mineralogical alteration rather than to the presence of PSD.MD grains. For the entire set of samples the success rate of the palaeointensity determinations is very low with 80 per cent of the samples rejected. Nevertheless, reliable mean archaeointensities have been obtained for two of the three kilns (MOA, 80.1 Â} 14.5 ÆĂT and MOB, 86.6 Â} 6.9 ÆĂT at the latitude of Paris). The high field strength and the archaeomagnetic directions determined, combined with previous published data, provide further evidence for important changes of the Earth magnetic field in Europe during the first half of the first millennium BC. These large variations of the geomagnetic field during the Iron Ages indicate that archaeomagnetism is highly suitable for dating of structures from this period
An improved genome of the model marine alga Ostreococcus tauri unfolds by assessing Illumina de novo assemblies
Background:
Cost effective next generation sequencing technologies now enable the production of genomic datasets for many novel planktonic eukaryotes, representing an understudied reservoir of genetic diversity. O. tauri is the smallest free-living photosynthetic eukaryote known to date, a coccoid green alga that was first isolated in 1995 in a lagoon by the Mediterranean sea. Its simple features, ease of culture and the sequencing of its 13 Mb haploid nuclear genome have promoted this microalga as a new model organism for cell biology. Here, we investigated the quality of genome assemblies of Illumina GAIIx 75 bp paired-end reads from Ostreococcus tauri, thereby also improving the existing assembly and showing the genome to be stably maintained in culture.
Results:
The 3 assemblers used, ABySS, CLCBio and Velvet, produced 95% complete genomes in 1402 to 2080 scaffolds with a very low rate of misassembly. Reciprocally, these assemblies improved the original genome assembly by filling in 930 gaps. Combined with additional analysis of raw reads and PCR sequencing effort, 1194 gaps have been solved in total adding up to 460 kb of sequence. Mapping of RNAseq Illumina data on this updated genome led to a twofold reduction in the proportion of multi-exon protein coding genes, representing 19% of the total 7699 protein coding genes. The comparison of the DNA extracted in 2001 and 2009 revealed the fixation of 8 single nucleotide substitutions and 2 deletions during the approximately 6000 generations in the lab. The deletions either knocked out or truncated two predicted transmembrane proteins, including a glutamate-receptor like gene.
Conclusion:
High coverage (>80 fold) paired-end Illumina sequencing enables a high quality 95% complete genome assembly of a compact ~13 Mb haploid eukaryote. This genome sequence has remained stable for 6000 generations of lab culture
The Complete Genome of Propionibacterium freudenreichii CIRM-BIA1T, a Hardy Actinobacterium with Food and Probiotic Applications
Background: Propionibacterium freudenreichii is essential as a ripening culture in Swiss-type cheeses and is also considered for its probiotic use [1]. This species exhibits slow growth, low nutritional requirements, and hardiness in many habitats. It belongs to the taxonomic group of dairy propionibacteria, in contrast to the cutaneous species P. acnes. The genome of the type strain, P. freudenreichii subsp. shermanii CIRM-BIA1 (CIP 103027T), was sequenced with an 11-fold coverage. Methodology/Principal Findings: The circular chromosome of 2.7 Mb of the CIRM-BIA1 strain has a GC-content of 67% and contains 22 different insertion sequences (3.5% of the genome in base pairs). Using a proteomic approach, 490 of the 2439 predicted proteins were confirmed. The annotation revealed the genetic basis for the hardiness of P. freudenreichii, as the bacterium possesses a complete enzymatic arsenal for de novo biosynthesis of aminoacids and vitamins (except panthotenate and biotin) as well as sequences involved in metabolism of various carbon sources, immunity against phages, duplicated chaperone genes and, interestingly, genes involved in the management of polyphosphate, glycogen and trehalose storage. The complete biosynthesis pathway for a bifidogenic compound is described, as well as a high number of surface proteins involved in interactions with the host and present in other probiotic bacteria. By comparative genomics, no pathogenicity factors found in P. acnes or in other pathogenic microbial species were identified in P. freudenreichii, which is consistent with the Generally Recognized As Safe and Qualified Presumption of Safety status of P. freudenreichii. Various pathways for formation of cheese flavor compounds were identified: the Wood-Werkman cycle for propionic acid formation, amino acid degradation pathways resulting in the formation of volatile branched chain fatty acids, and esterases involved in the formation of free fatty acids and esters. Conclusions/Significance: With the exception of its ability to degrade lactose, P. freudenreichii seems poorly adapted to dairy niches. This genome annotation opens up new prospects for the understanding of the P. freudenreichii probiotic activity
Life-Cycle and Genome of OtV5, a Large DNA Virus of the Pelagic Marine Unicellular Green Alga Ostreococcus tauri
Large DNA viruses are ubiquitous, infecting diverse organisms ranging from algae to man, and have probably evolved from an ancient common ancestor. In aquatic environments, such algal viruses control blooms and shape the evolution of biodiversity in phytoplankton, but little is known about their biological functions. We show that Ostreococcus tauri, the smallest known marine photosynthetic eukaryote, whose genome is completely characterized, is a host for large DNA viruses, and present an analysis of the life-cycle and 186,234 bp long linear genome of OtV5. OtV5 is a lytic phycodnavirus which unexpectedly does not degrade its host chromosomes before the host cell bursts. Analysis of its complete genome sequence confirmed that it lacks expected site-specific endonucleases, and revealed the presence of 16 genes whose predicted functions are novel to this group of viruses. OtV5 carries at least one predicted gene whose protein closely resembles its host counterpart and several other host-like sequences, suggesting that horizontal gene transfers between host and viral genomes may occur frequently on an evolutionary scale. Fifty seven percent of the 268 predicted proteins present no similarities with any known protein in Genbank, underlining the wealth of undiscovered biological diversity present in oceanic viruses, which are estimated to harbour 200Mt of carbon
Archaeomagnetic dating of archaeological baked clays in France during the first millennium BC : improvements of the secular variation curves of the direction and intensity of the geomagnetic field
Lâobjectif de ce travail est lâamĂ©lioration des courbes de variation sĂ©culaire de la direction (inclinaison I et dĂ©clinaison D) et de lâintensitĂ© (F) du champ magnĂ©tique terrestre en Europe occidentale durant le premier millĂ©naire av. J.-C. 47 fours, foyers et lots de tessons cĂ©ramiques ont Ă©tĂ© Ă©tudiĂ©s pour constituer de nouvelles structures de rĂ©fĂ©rence. La datation du moment dâacquisition de lâaimantation a Ă©tĂ© dĂ©finie en analysant lâensemble des informations archĂ©ologiques et chronomĂ©triques disponibles sur les sites. 39 nouvelles archĂ©odirections ont Ă©tĂ© obtenues aprĂšs dĂ©saimantations thermique et par champ alternatif. Les 18 archĂ©ointensitĂ©s ont Ă©tĂ© dĂ©terminĂ©es par le protocole de Thellier-Thellier et gĂ©nĂ©ralement corrigĂ©es des effets de lâanisotropie et de la vitesse de refroidissement. Les courbes de variation sĂ©culaire françaises, construites par moyenne mobile et par la statistique hiĂ©rarchique bayĂ©sienne, ont Ă©tĂ© Ă©tendues jusquâen 1500 av. J.-C. pour la direction et jusquâen 800 av. J.-C. pour lâintensitĂ©. Lâinclinaison a une variation non monotone entre 65 et 75° entre 1500 et 0 av. J.-C. Les variations de la dĂ©clinaison et de lâintensitĂ© sont trĂšs fortes avec un maximum en 800 av. J.-C. (30° pour D et 90 ”T pour F) et un minimum (-5° pour D et 60”T pour F) en 250 av. J.-C. LâinterprĂ©tation gĂ©omagnĂ©tique de la variation sĂ©culaire est difficile en raison des lacunes des jeux de donnĂ©es de rĂ©fĂ©rence hors Europe. Ces nouvelles courbes plus fiables amĂ©liorent la datation archĂ©omagnĂ©tique au premier millĂ©naire av. J.-C. et Ă©tendent son application Ă lâĂąge du Bronze final. Du fait de la forte variation sĂ©culaire, le premier Ăąge du Fer est la pĂ©riode la plus propice.This study aims to improve the Western Europe secular variation curve of the direction (inclination I and declination D) and the intensity (F) of the Earthâs magnetic field during the first millennium BC. New archaeomagnetic reference data were obtained from 47 kilns, hearths and sets of pottery sherds with precise magnetization acquisition ages determined through a comprehensive review of available archaeological and chronometric informations. 39 new archaeodirections were computed after thermal and alternating field demagnetizations and 18 new archaeointensities were determined by the Thellier-Thellier protocol with anisotropy and cooling rate corrections. The new French secular variation curves, built using hierarchical bayesian statistics, were extended to 1500BC for the direction and to 800BC for the intensity. Inclination vary non-monotonously (between 65 and 75°) between 1500BC and 0AD. Variations in declination and intensity are very strong with a maximum at 800BC (30° for D and 90”T for F) and a minimum at 250BC (-5° for D and 60”T for F). Interpreting the geomagnetic significance of this strong variation is hindered by the scarcity of data outside Europe. However it provides a useful marker for reliable archaeomagnetic dating in Western Europe during the Iron Age, especially during the Early Iron Age thanks to the strong secular variation. The new directional curve also allows the extension of archaeomagnetic dating to the Final Bronze Age
Datation par archéomagnétisme des terres cuites archéologiques en France au premier millénaire av. J.-C. : étalonnage des variations du champ géomagnétique en direction et intensité
This study aims to improve the Western Europe secular variation curve of the direction (inclination I and declination D) and the intensity (F) of the Earthâs magnetic field during the first millennium BC. New archaeomagnetic reference data were obtained from 47 kilns, hearths and sets of pottery sherds with precise magnetization acquisition ages determined through a comprehensive review of available archaeological and chronometric informations. 39 new archaeodirections were computed after thermal and alternating field demagnetizations and 18 new archaeointensities were determined by the Thellier-Thellier protocol with anisotropy and cooling rate corrections. The new French secular variation curves, built using hierarchical bayesian statistics, were extended to 1500BC for the direction and to 800BC for the intensity. Inclination vary non-monotonously (between 65 and 75°) between 1500BC and 0AD. Variations in declination and intensity are very strong with a maximum at 800BC (30° for D and 90”T for F) and a minimum at 250BC (-5° for D and 60”T for F). Interpreting the geomagnetic significance of this strong variation is hindered by the scarcity of data outside Europe. However it provides a useful marker for reliable archaeomagnetic dating in Western Europe during the Iron Age, especially during the Early Iron Age thanks to the strong secular variation. The new directional curve also allows the extension of archaeomagnetic dating to the Final Bronze Age.Lâobjectif de ce travail est lâamĂ©lioration des courbes de variation sĂ©culaire de la direction (inclinaison I et dĂ©clinaison D) et de lâintensitĂ© (F) du champ magnĂ©tique terrestre en Europe occidentale durant le premier millĂ©naire av. J.-C. 47 fours, foyers et lots de tessons cĂ©ramiques ont Ă©tĂ© Ă©tudiĂ©s pour constituer de nouvelles structures de rĂ©fĂ©rence. La datation du moment dâacquisition de lâaimantation a Ă©tĂ© dĂ©finie en analysant lâensemble des informations archĂ©ologiques et chronomĂ©triques disponibles sur les sites. 39 nouvelles archĂ©odirections ont Ă©tĂ© obtenues aprĂšs dĂ©saimantations thermique et par champ alternatif. Les 18 archĂ©ointensitĂ©s ont Ă©tĂ© dĂ©terminĂ©es par le protocole de Thellier-Thellier et gĂ©nĂ©ralement corrigĂ©es des effets de lâanisotropie et de la vitesse de refroidissement. Les courbes de variation sĂ©culaire françaises, construites par moyenne mobile et par la statistique hiĂ©rarchique bayĂ©sienne, ont Ă©tĂ© Ă©tendues jusquâen 1500 av. J.-C. pour la direction et jusquâen 800 av. J.-C. pour lâintensitĂ©. Lâinclinaison a une variation non monotone entre 65 et 75° entre 1500 et 0 av. J.-C. Les variations de la dĂ©clinaison et de lâintensitĂ© sont trĂšs fortes avec un maximum en 800 av. J.-C. (30° pour D et 90 ”T pour F) et un minimum (-5° pour D et 60”T pour F) en 250 av. J.-C. LâinterprĂ©tation gĂ©omagnĂ©tique de la variation sĂ©culaire est difficile en raison des lacunes des jeux de donnĂ©es de rĂ©fĂ©rence hors Europe. Ces nouvelles courbes plus fiables amĂ©liorent la datation archĂ©omagnĂ©tique au premier millĂ©naire av. J.-C. et Ă©tendent son application Ă lâĂąge du Bronze final. Du fait de la forte variation sĂ©culaire, le premier Ăąge du Fer est la pĂ©riode la plus propice
Datation archéomagnétique des fours de potiers du quartier artisanal et du four des bains hellénistiques.
International audienc
La restitution des structures de cuisson de lâĂąge du Fer en Italie mĂ©ridionale : dialogue entre archĂ©ologie et archĂ©omagnĂ©tisme
International audienc
Datation archéomagnétique : contribution du champ géomagnétique à l'archéologie
National audienceLa datation archĂ©omagnĂ©tique repose sur l'enregistrement par les terres cuites d'une aimantation thermorĂ©manente parallĂšle et proportionnelle au champ magnĂ©tique terrestre ambiant lors de leur derniĂšre chauffe. Les fours, foyers et lots de briques et tuiles sont prĂ©levĂ©s sur les sites archĂ©ologiques. Leur aimantation est mesurĂ©e au laboratoire pour obtenir la direction et l'intensitĂ© du champ magnĂ©tique ancien. Pour la datation, ces valeurs sont comparĂ©es Ă des courbes de variation sĂ©culaire rĂ©gionales qui sont construites Ă partir de donnĂ©es de rĂ©fĂ©rence. La datation archĂ©omagnĂ©tique n'est ainsi envisageable que dans les pĂ©riodes et rĂ©gions pour lesquelles un rĂ©fĂ©rentiel a pu ĂȘtre Ă©tabli. En Europe de l'Ouest, les rĂ©fĂ©rentiels, trĂšs complets, remontent jusqu'en 1500 av. J.-C
Oppidum de Gondole (commune du Centre, Puy de DÎme) Four 36 et puits 209: Analyse archéomagnétique REN-2010-15
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