Experimental fossilisation of viruses from extremophilic Archaea

The role of viruses at different stages of the origin of life has recently been reconsidered. It appears that viruses may have accompanied the earliest forms of life, allowing the transition from an RNA to a DNA world and possibly being involved in the shaping of tree of life in the three domains that we know presently. In addition, a large variety of viruses has been recently identified in extreme environments, hosted by extremophilic microorganisms, in ecosystems considered as analogues to those of the early Earth. Traces of life on the early Earth were preserved by the precipitation of silica on the organic structures. We present the results of the first experimental fossilisation by silica of viruses from extremophilic Archaea (SIRV2 – <i>Sulfolobus islandicus</i> rod-shaped virus 2, TPV1 – <i>Thermococcus prieurii</i> virus 1, and PAV1 – <i>Pyrococcus abyssi</i> virus 1). Our results confirm that viruses can be fossilised, with silica precipitating on the different viral structures (proteins, envelope) over several months in a manner similar to that of other experimentally and naturally fossilised microorganisms. This study thus suggests that viral remains or traces could be preserved in the rock record although their identification may be challenging due to the small size of the viral particles

Genomics and metagenomics of trimethylamine-utilizing Archaea in the human gut microbiome

International audienceThe biological significance of Archaea in the human gut microbiota is largely unclear. We recently reported genomic and biochemical analyses of the Methanomassiliicoccales, a novel order of methanogenic Archaea dwelling in soil and the animal digestive tract. We now show that these Methanomassiliicoccales are present in published microbiome data sets from eight countries. They are represented by five Operational Taxonomic Units present in at least four cohorts and phylogenetically distributed into two clades. Genes for utilizing trimethylamine (TMA), a bacterial precursor to an atherosclerogenic human metabolite, were present in four of the six novel Methanomassiliicoccales genomes assembled from ELDERMET metagenomes. In addition to increased microbiota TMA production capacity in long-term residential care subjects, abundance of TMA-utilizing Methanomassiliicoccales correlated positively with bacterial gene count for TMA production and negatively with fecal TMA concentrations. The two large Methanomassiliicoccales clades have opposite correlations with host health status in the ELDERMET cohort and putative distinct genomic signatures for gut adaptation

Die Rhythmik der Koerperkerntemperatur von Legehennen unter verschiedenen Haltungsbedingungen. Ein Beitrag zur Suche nach objektivierbaren Kriterien fuer eine artgerechte Haltung von Legehennen

Available from: Zentralstelle fuer Agrardokumentation und -information (ZADI), Villichgasse 17, D-53177 Bonn / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Abiotic syntheses of pyrite: clues to assess the biogenicity of pyrite spherules

International audienceLife proliferates almost everywhere on Earth but determining whether or not hyperthermophile microorganisms have colonised a given hydrothermal environment, such as black smoker chimneys, remains challenging. Some mineral phases like pyrite spherules have been proposed to possibly serve as biosignatures. Yet, little is known about the specificities of pyrites produced via abiotic processes under hydrothermal conditions, making these pyrite spherules only potential biosignatures at best. Here, we report results of abiotic syntheses of pyrites under conditions reproducing those existing in the chimneys of black smokers, in the presence or in the absence of various organic compounds. We experimentally show that no pyrite is produced in the absence of organic material, whereas the chemical nature of the organic compounds controls the shape and crystallinity of the pyrite produced. The presence of complex organic matter, here compounds derived from lysed cells, appears necessary for the production of pyrite spherules previously described as biogenic, suggesting that the pyrite spherules detected in natural black smokers may not be considered as biogenic stricto sensu, but rather as proxies of the presence of microorganisms

Increase of positive supercoiling in a hyperthermophilic archaeon after UV irradiation

International audienceDiverse DNA repair mechanisms are essential to all living organisms. Some of the most widespread repair systems allow recovery of genome integrity in the face of UV radiation. Here, we show that the hyperthermophilic archaeon Thermococcus nautili possesses a remarkable ability to recovery from extreme chromosomal damage. Immediately following UV irradiation, chromosomal DNA of T. nautili is fragmented beyond recognition. However, the extensive UV-induced double-stranded breaks (DSB) are repaired over the course of several hours, allowing restoration of growth. DSBs also disrupted plasmid DNA in this species. Similar to the chromosome, plasmid integrity was restored during an outgrowth period. Intriguingly, the topology of recovered pTN1 plasmids differed from control strain by being more positively supercoiled. As reverse gyrase (RG) is the only enzyme capable of inducing positive supercoiling, our results suggest the activation of RG activity by UV-induced stress. We suggest simple UV stress could be used to study archaeal DNA repair and responses to DSB

Gene resolution Hi-C reveals Euryarchaeal genomes are folded into SMC-dependent loops and domains, but lack transcription-mediated compartmentalization

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Thermococcus nautili sp. nov., a hyperthermophilic archaeon isolated from a hydrothermal deep-sea vent

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