Distribution of bacteria and associated minerals in the gill chamber of the vent shrimp Rimicaris exoculata and related biogeochemical processes

in Marine Ecology. Progress Series (2004), 284

The shrimp Rimicaris exoculata dominates the megafauna of some Mid-Atlantic Ridge hydrothermal vent fields. This species harbours a rich bacterial epibiosis inside its gill chamber. At the 'Rainbow' vent ... [more ▼]

The shrimp Rimicaris exoculata dominates the megafauna of some Mid-Atlantic Ridge hydrothermal vent fields. This species harbours a rich bacterial epibiosis inside its gill chamber. At the 'Rainbow' vent site (36degrees 14.0'N), the epibionts are associated with iron oxide deposits. Investigation of both bacteria and minerals by scanning electron microscopy (SEM) and X-ray microanalysis (EDX) revealed 3 distinct compartments in the gill chamber: (1) the lower pre-branchial chamber, housing bacteria but devoid of minerals; (2) the 'true' branchial chamber, containing the gills and devoid of both bacteria and minerals; and (3) the upper pre-branchial chamber, housing the main ectosymbiotic bacterial community and associated mineral deposits. Our chemical and temperature data indicated that abiotic iron oxidation appears to be kinetically inhibited in the environment of the shrimps, which would explain the lack of iron oxide deposits in the first 2 compartments. We propose that iron oxidation is microbially promoted in the third area. The discrepancy between the spatial distribution of bacteria and minerals suggests that different bacterial metabolisms are involved in the first and third compartments. A possible explanation lies in the modification of physico-chemical conditions downstream of the gills that would reduce the oxygen content and favours the development of bacterial iron-oxidizers in this Fe-II-rich environment. A potential role of such iron-oxidizing symbionts in the shrimp diet is suggested. This would be unusual for hydrothermal ecosystems, in which most previously described symbioses rely on sulphide or methane as an energy source. [less ▲]

Mineralogical gradients associated with alvinellids at deep-sea hydrothermal vents

in Deep-Sea Research Part I-Oceanographic Research Papers (2003), 50(2), 269-280

Alvinella pompejana and Alvinella caudata live in organic tubes on active sulphide chimney walls at deep-sea hydrothermal vents. These polychaete annelids are exposed to extreme thermal and chemical ... [more ▼]

Alvinella pompejana and Alvinella caudata live in organic tubes on active sulphide chimney walls at deep-sea hydrothermal vents. These polychaete annelids are exposed to extreme thermal and chemical gradients and to intense mineral precipitation. This work points out that mineral particles associated with Pompeii worm (A. pompejana and A. caudata) tubes constitute useful markers for evaluating the chemical characteristics of their micro-environment. The minerals associated with these worm tubes were analysed on samples recovered from an experimental alvinellid colony, at different locations in the vent fluid-seawater interface. Inhabited tubes from the most upper and lower parts of the colony were analysed by light and electron microscopies, X-ray microanalysis and X-ray diffraction. A change was observed from a Fe-Zn-S mineral assemblage to a Zn-S assemblage at the millimeter scale from the outer to the inner face of a tube. A similar gradient in proportions of minerals was observed at a decimeter scale from the lower to the upper part of the colony. The marcasitc/pyrite ratio of iron disulphides also displays a steep decrease along the few millimeters adjacent to the external tube surface. The occurrence of these gradients indicates that the microenvironment within the tube differs from that outside the tube, and suggests that the tube wall acts as an efficient barrier to the external environment. (C) 2003 Elsevier Science Ltd. All rights reserved. [less ▲]

Karst in granitic rocks, South Cameroon: cave genesis and silica and taranakite speleothems

in Terra Nova (2002), 14(5), 355-362

A cave in granitic rocks was studied in Mezesse, South Cameroon. Coralloid speleothems, draperies and dissolution traces on the cave walls attest to its truly karstic nature. The speleothems consist of ... [more ▼]

A cave in granitic rocks was studied in Mezesse, South Cameroon. Coralloid speleothems, draperies and dissolution traces on the cave walls attest to its truly karstic nature. The speleothems consist of microlayers of opal and taranakite (K,NH4)Al-3(PO4)(3)(OH).9H(2)O. They indicate a significant mobilization of silica, Al and K from granite during the formation of the cave. Identification of silicified bacteria in the speleothems layers suggests a possible role of these micro-organisms in silica deposition. The presence of taranakite and of silicified organic remains within the speleothems lead to a better understanding of the genesis of the cave. [less ▲]

Does sulfide detoxication occur in the gills of the hydrothermal vent shrimp, Rimicaris exoculata?

in Comptes Rendus Biologies (2002), 325

Karst granitique au Sud Cameroun. Analyses de concrétions siliceuses coralloïdes et genèse d’une grotte

Poster (1999)

Study of siliceous karst genesis in Eastern Niger. Microscopy and analysis of speleothems

in Zeitschrift für Geomorphologie (1998), 42(2), 129-142

Ultrastructure and cytochemistry of the early calcification site and of its mineralizing organic matrix in Paracentrotus lividus (Echinodermata: Echinoidea)

in Histochemistry & Cell Biology (1998), 110

"Exolysosomes", Enzyme-Containing Vesicles in the Ecdysial Space of Molting Crabs

in Journal of Structural Biology (1997), 119(3), 247-59

Free vesicle-like bodies (VLBs) present in the ecdysial space of cuticle regions undergoing degradation during preecdysis of the Atlantic shore crab Carcinus maenas have been interpreted either as ... [more ▼]

Free vesicle-like bodies (VLBs) present in the ecdysial space of cuticle regions undergoing degradation during preecdysis of the Atlantic shore crab Carcinus maenas have been interpreted either as infectious organisms or as secretion structures associated with degradation of the old cuticle. Ultrastructural, cytochemical, and immunocytological investigations were performed to test these hypotheses and to see whether VLBs are peculiar to this crab species. Similar VLBs were systematically found in two other preecdysial crabs, Cancer pagurus and Macropipus puber. In Car, maenas, they originate during early premolt inside Golgi buddings and are often gathered into large vacuoles in epidermal cells. The histochemical azo-dye technique and a cerium-based cytochemical method revealed acid phosphatase activity in both the ecdysial space and the VLBs, while Feulgen's method and immunocytological labeling always failed to reveal any DNA or RNA in either the ecdysial space or the VLBs. We conclude that VLBs are not infectious organisms but "extracellular" cuticle-degrading organelles of lysosomal origin and propose to coin them "exolysosomes." [less ▲]

Microscopic observation of the retinal photoreceptor layer of the common barbel (Teleostei: Cyprinidae)

in Belgian Journal Of Zoology (1996), 126(1), 49-56

Light and electron microscopic observations show that cones-belonging to four types are present in the retina of the common barbel Barbus barbus (L.): short single cones, long single cones, twin cones ... [more ▼]

Light and electron microscopic observations show that cones-belonging to four types are present in the retina of the common barbel Barbus barbus (L.): short single cones, long single cones, twin cones, and unequal double cones. They do not exhibit any particular arrangement. Estimates of cone density suggest that the common barbel has multichromatic vision but of low acuity and that no difference exists between the lower and the upper parts of the retina. Both cone density (approximately 3000 units/mm(2)) and the proportion of double cones to single cones (approximately 1:3) are low. The view that the barbel has an inferior colour vision is in good agreement with the fact that this species is active mainly at twilight, but with diurnal activity during spawning. [less ▲]

Cytochemistry of the tergite epicuticle of Glomeris marginata (Villers) (MYRIAPODA, DIPLOPODA): preliminary experimental results

in Mémoires du Muséum d'Histoire naturelle (Paris) - Acta Myriapodologica (1996), 169