Molecular gene organisation and secondary structure of the mitochondrial large subunit ribosomal RNA from the cultivated Basidiomycota Agrocybe aegerita: a 13 kb gene possessing six unusual nucleotide extensions and eight introns.
The complete gene sequence and secondary structure of the mitochondrial LSU rRNA from the cultivated Basidiomycota Agrocybe aegerita was derived by chromosome walking. The A.aegerita LSU rRNA gene (13 526 nt) represents, to date, the longest described, due to the highest number of introns (eight) and the occurrence of six long nucleotidic extensions. Seven introns belong to group I, while the intronic sequence i5 constitutes the first typical group II intron reported in a fungal mitochondrial LSU rDNA. As with most fungal LSU rDNA introns reported to date, four introns (i5-i8) are distributed in domain V associated with the peptidyl-transferase activity. One intron (i1) is located in domain I, and three (i2-i4) in domain II. The introns i2-i8 possess homologies with other fungal, algal or protozoan introns located at the same position in LSU rDNAs. One of them (i6) is located at the same insertion site as most Ascomycota or algae LSU introns, suggesting a possible inheritance from a common ancestor. On the contrary, intron i1 is located at a so-far unreported insertion site. Among the six unusual nucleotide extensions, five are located in domain I and one in domain V. This is the first report of a mitochondrial LSU rRNA gene sequence and secondary structure for the whole Basidiomycota division.
(Nucleic Acids Research. vol. 27, n° 0305-1048, pp. 1754-1761, 01/04/1999)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Chemical and isotopic constraints to varied formation processes for the brines of different deeps in the Red Sea.
Almost all Red Sea deeps contain metal-rich sediments covered by brine pools. It is generally agreed that these metal-rich deposits precipitated from overlying metal-rich brines that originated from migrating hydrothermal fluids. No brine pool has ever been reported in Thetis Deep, inciting us to evaluate if such a brine layer ever occurred in the deep during the past. In order to address that questioning, a study combining mineralogical, geochemical (major-, minor-, rare-earth elements) and isotopic (Sr. Nd. Pb) approaches was completed on cored sediments and extracted interstitial waters from inside and outside the deep.;The sediments have an overall hydrothermal origin, as shown by the REE concentrations and patterns, metal contents, and Pb-Nd isotopic data, all pointing to a mantle signature. The intensity of the hydrothermal activity varied with time in the deep; the most intense episode resulting in an almost pure Fe-oxi-hydroxide layer. Varied chemical arguments, especially the Zr and REE data of the sediments, favor the fact that the whole sedimentation in Thetis Deep occurred in the absence of a stable, salt-rich and mineralized brine pool, and that no brine layer ever existed. This conclusion is supported by the constant Sr isotope composition of the sediment and its interstitial waters that are almost identical to that of the Red Sea seawater. The study also suggests that hydrothermal activity monitored fluid supplies that interacted differently with seawater in the different Red Sea deeps, resulting in an overall formation of metal-rich sediments, but along varied local conditions. (C) 2009 Elsevier B.V. All rights reserved.
(28/03/1999)
LHyGeS, ENGEES, UNISTRA, INSU - CNRS, CNRS, UAG, INSU - CNRS, UM, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Does the slipper limpet (Crepidula fornicata, L.) impair oyster growth and zoobenthos biodiversity? A revisited hypothesis
The Prosobranch Gastropod Crepidula fornicata was introduced into Great Britain at the end of the 19th century from North America, upon imported oysters Crassostrea virginica. Since then, it has invaded sheltered coasts of the North West Atlantic and Mediterranean Sea. C. fornicata proliferation has often generated social conflicts due to three main causes: (1) trophic competition with other suspension feeders, e.g. the cultivated oyster Crassostrea gigas; (2) spatial competition with macrozoobenthos; and (3) enhancement of silt and clay sedimentation. The effects of C. fornicata on C. gigas growth and on macrozoobenthic density and diversity have been documented through field experiments in an oyster park of Arcachon Bay (France). Densities of C. gigas and biomass of C. fornicata were manipulated over a period of 247 days within field enclosures at low water level to test: (1) oyster growth, condition index and mortality; (2) zoobenthic community alterations (abundance, biomass, species richness). From this small-scale experiment, it was shown that none of these investigated parameters was significantly affected by the presence of C. fornicata. However, faunal assemblages were modified in enclosures compared to external bare sands, due to adding a hard substrata over a soft sediment.
(Journal of Experimental Marine Biology and Ecology. vol. 235, n° 0022-0981, pp. 105-124, 01/03/1999)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Glacial and Interglacial Hydrological Changes in the North Atlantic Ocean
(pp. 83-101, 21/02/1999)
LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, PALEOCEAN, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Fine-grained sediment budget on the continental margin of the Bay of Biscay
Under present-day conditions, rivers are the main source of fine sediments dispersed to the Bay of Biscay. They deliver about 2.5×10 6 t yr -1 of continental fine sediments, 60% of which is derived from the Gironde estuary. Of this flux, 65% is believed stored on the shelf. Two kinds of mud fields can be found in the Bay of Biscay: coastal mud and shelf mud belts. The total mass of fine sediments stored during the past 2000 years is 3.2×10 9 t. Consequently, about 0.9×10 6 t yr -1 could reach the shelf edge and eventually the open sea. From this amount of displaced material and the deposition surface areas, an evaluation of sediment fluxes across the margin during the late Holocene period is discussed. This evaluation is compared with results obtained from ECOsystéme du canyon du cap-FERret (ECOFER) data from sediment traps and surficial box cores.
(Deep Sea Research Part II: Topical Studies in Oceanography. vol. 46, n° 0967-0645, pp. 2205-2220, 21/02/1999)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Spatial and temporal patterns of downward particle fluxes on the continental slope of the Bay of Biscay (northeastern Atlantic)
no abstract
(Deep Sea Research Part II: Topical Studies in Oceanography. vol. 46, n° 0967-0645, pp. 2101--2146, 21/02/1999)
CEFREM, UPVD, INSU - CNRS, CNRS, CEREGE, IRD, INRA, AMU, CdF (institution), INSU - CNRS, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Effect of macrofaunal bioturbation on bacterial distribution in marine sandy sediments, with special reference to sulphur-oxidising bacteria
We have studied the impact of the bioturbating macrofauna, in particular the lugworm Arenicola marina and the bivalve Cerastoderma edule, on abundances and distribution patterns of total bacteria and of bacteria of selected functional groups in sandy intertidal sediments. The selected groups comprised the colourless sulphur-oxidising bacteria and the anoxygenic phototrophic bacteria, which are expected to occupy small zones at the oxygen-sulphide interface in stable (non-bioturbated) sediments. The presence of a wooden wreck buried in the sediment at 10 cm depth within a large area of intertidal sand flat colonised by lugworms provided a unique opportunity to confront field observations with laboratory simulations. The site with the wooden wreck, which was used as control site, was devoid of both A. marina and C. edule, while the composition of the rest of the zoobenthic community was rather similar to that of the surrounding area. In the field, the density of total bacteria was approximately one order of magnitude higher in the control site than in the natural (bioturbated) site. This can be explained by the higher contents of silt and clay particles (higher surface-area/volume ratio) and higher total organic-carbon contents found at the control site. It appears that the presence of macrofauna affects sedimentation processes, which indirectly influence bacterial dynamics. Samples from the control site have been incubated in the laboratory with A. marina and C. edule added (bioturbated core), while an unamended core served as a control. The laboratory experiments contrasted with the field observations, because it was found that total bacteria were actually higher in the deeper layers of the bioturbated core. Moreover, the populations were more homogeneous (less stratified) and colourless sulphur bacteria were on average less numerous in the bioturbated core. In general, laboratory incubations resulted in a decrease of total bacteria with a concomitant increase of colourless and phototrophic sulphur-oxidising bacteria and thus in modifications of the bacterial community structure. Hence, our results demonstrate that care must be taken in extrapolating results from laboratory experiments (e.g. mesocosm research) to field situations.
(Journal of Sea Research (JSR). vol. 41, n° 1385-1101, pp. 269-279, 21/02/1999)
IPREM, UPPA, INC-CNRS, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Refractory organic matter in sediments from the North-West African upwelling system: abundance, chemical structure and origin
(Organic Geochemistry. vol. 30, n° 0146-6380, pp. 101-117, 21/02/1999)
UPMC, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LPCM, UPMC, CNRS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, ENS-PSL, PSL
Live benthic foraminiferal faunas off Cape Blanc, NW-Africa: Community structure and microhabitats
(Deep Sea Research Part I: Oceanographic Research Papers. vol. 45, n° 0967-0637, pp. 2157-2188, 01/12/1998)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, OCEANIS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA
Glacial–interglacial changes in the accumulation rates of major biogenic components in Southern Indian Ocean sediments
(Journal of Marine Systems. vol. 17, n° 0924-7963, pp. 527-539, 01/11/1998)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, PALEOCEAN, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA