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Christaki U.,University of Lille Nord de France | Van Wambeke F.,Aix - Marseille University | Lefevre D.,Aix - Marseille University | Lagaria A.,University of Lille Nord de France | And 16 more authors.

The abundance and activity of the major members of the heterotrophic microbial community ĝ€" from viruses to ciliates ĝ€" were studied along a longitudinal transect across the Mediterranean Sea in the summer of 2008. The Mediterranean Sea is characterized by a west to-east gradient of deepening of DCM (deep chlorophyll maximum) and increasing oligotrophy reflected in gradients of biomass and production. However, within this well documented longitudinal trend, hydrological mesoscale features exist and likely influence microbial dynamics. Here we present data from a W-E transect of 17 stations during the period of summer stratification. Along the transect the production and fate of organic matter was investigated at three selected sites each one located in the centre of an anticyclonic eddy: in the Algero-Provencal Basin (St. A), the Ionian Basin (St. B), and the Levantine Basin (St. C). The 3 geographically distant eddies showed low values of the different heterotrophic compartments of the microbial food web, and except for viruses in site C, all integrated (0ĝ€"150 m) stocks were higher in reference stations located in the same basin outside the eddies. During our study the 3 eddies showed equilibrium between GPP (Gross Primary Production) and DCR (Dark Community Respiration). Integrated PPp (Particulate Primary Production) values at A, B and C varied from ∼140 to ∼190 mg C mĝ̂'2. © Author(s) 2011. Source

Roux S.,University Blaise Pascal | Roux S.,Laboratoire Microorganismes Genome et Environnement | Krupovic M.,Institute Pasteur Paris | Poulet A.,University Blaise Pascal | And 5 more authors.

Recent studies suggest that members of the Microviridae (a family of ssDNA bacteriophages) might play an important role in a broad spectrum of environments, as they were found in great number among the viral fraction from seawater and human gut samples. 24 completely sequenced Microviridae have been described so far, divided into three distinct groups named Microvirus, Gokushovirinae and Alpavirinae, this last group being only composed of prophages. In this study, we present the analysis of 81 new complete Microviridae genomes, assembled from viral metagenomes originating from various ecosystems. The phylogenetic analysis of the core genes highlights the existence of four groups, confirming the three sub-families described so far and exhibiting a new group, named Pichovirinae. The genomic organizations of these viruses are strikingly coherent with their phylogeny, the Pichovirinae being the only group of this family with a different organization of the three core genes. Analysis of the structure of the major capsid protein reveals the presence of mushroom-like insertions conserved within all the groups except for the microviruses. In addition, a peptidase gene was found in 10 Microviridae and its analysis indicates a horizontal gene transfer that occurred several times between these viruses and their bacterial hosts. This is the first report of such gene transfer in Microviridae. Finally, searches against viral metagenomes revealed the presence of highly similar sequences in a variety of biomes indicating that Microviridae probably have both an important role in these ecosystems and an ancient origin. © 2012 Roux et al. Source

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