Philippe Crassous

Direct observation of intense turbidity current activity in the Zaire submarine valley at 4000 m water depth

A large turbidity current was detected in the Zaire submarine valley at 4000 m water depth. Current meters, turbidimeter and sediment trap deployed on a mooring located in the channel axis, although they were damaged, recorded the signature of a very high energy event. An average velocity of more than 121 cm s−1 was measured 150 m above the channel floor. Coarse sand and plant debris were collected at 40 m height. The turbidity current clearly overflowed the edges of the valley as demonstrated by the large quantity of turbiditic material (464 mg organic carbon m−2 d−1) found in the sediment trap moored 13 km south from the channel axis.

Caminibacter hydrogeniphilus gen. nov., sp. nov., a novel thermophilic, hydrogen-oxidizing bacterium isolated from an East Pacific Rise hydrothermal vent

A novel thermophilic, anaerobic, hydrogen-oxidizing bacterium, designated strain AM1116T, was isolated from an East Pacific Rise hydrothermal vent sample. The cells were rod-shaped (1.01-5 x 0.5 microm), motile with polar flagella. They grew at temperatures between 50 and 70 degrees C (optimum 60 degrees C; doubling time approximately 1.5 h), at between pH 5.0 and 7.5 (optimum around pH 5.5-6.0) and in between 10 and 40 g NaCl l(-1) (optimum 20-25 g l(-1)). Cells grew chemolithoautotrophically in a H2/CO2 atmosphere (80:20; 200 kPa). Poor heterotrophic growth was observed on complex organic substrates. Elemental sulphur and nitrate served as electron acceptors, respectively yielding hydrogen sulphide and ammonia (doubling times were equal with the two electron acceptors). In contrast, when cystine was used as electron acceptor, growth was poor. The G+C content of the genomic DNA was 29 +/- 1 mol %. Phylogenetic analyses of the 16S rRNA gene located the strain within the epsilon-Proteobacteria, in the bacterial domain. On the basis of 16S rDNA sequence comparisons, physiological and biochemical characteristics, it is proposed that the isolate should be described as the type species of a new genus, Caminibacter gen. nov., as Caminibacter hydrogeniphilus sp. nov. The type strain is strain AM1116T (= DSM 14510T = CIP 107140T).

Detection of polycyclic aromatic hydrocarbon (PAH) compounds in artificial sea-water using surface-enhanced Raman scattering (SERS)

This paper reports an accurate synthesis of surface-enhanced Raman scattering (SERS) active substrates, based on gold colloidal monolayer, suitable for in situ environmental analysis. Quartz substrates were functionalized by silanization with (3-mercaptopropyl)trimethoxysilane (MPMS) or (3-aminopropyl)trimethoxysilane (APTMS) and they subsequently reacted with colloidal suspension of gold metal nanoparticles: respectively, the functional groups SH and NH(2) bound gold nanoparticles. Gold nanoparticles were prepared by the chemical reduction of HAuCl(4) using sodium tricitrate and immobilized onto silanized quartz substrates. Active substrate surface morphology was characterized with scanning electron microscopy (SEM) measurements and gold nanoparticles presented a diameter in the range 40-100 nm. Colloidal hydrophobic films, allowing nonpolar molecule pre-concentration, were obtained. The surfaces exhibit strong enhancement of Raman scattering from molecules adsorbed on the films. Spectra were recorded for two PAHs, naphthalene and pyrene, in artificial sea-water (ASW) with limits of detection (LODs) of 10 ppb for both on MPMS silanized substrates.

Caminicella sporogenes gen. nov., sp. nov., a novel thermophilic spore-forming bacterium isolated from an East-Pacific Rise hydrothermal vent

A novel thermophilic, anaerobic, strictly chemoorganoheterotrophic bacterium, designated as AM1114T, was isolated from a deep-sea hydrothermal vent sample from the East-Pacific Rise (EPR 13 degrees N). The cells were long (3-10 microm) rods, motile with peritrichous flagella, and exhibited a gram-negative cell wall ultrastructure. In the late stationary phase of growth, cells formed an ovoid, refractile, terminal endospore. They grew at 45-65 degrees C inclusive (optimum 55-60 degrees C; doubling time approx. 45 min), at pH 4.5-8.0 inclusive (optimum pH 7.5-8.0) and at sea salt concentrations of 20-60 g l(-1) inclusive (optimum 25-30 g l(-1)). Strain AM1114T was an obligately heterotrophic bacterium able to ferment a mixture of 20 amino acids, complex proteinaceous substrates (such as yeast extract, brain-heart infusion or peptone), and carbohydrates such as glucose, galactose or maltose. The main fermentation products on glucose/yeast extract/peptone/sulfur medium were hydrogen, carbon dioxide, butyrate, ethanol, acetate, formate and L-alanine. The G+C content of the genomic DNA (determined by thermal denaturation) was 24.2+/-1 mol%. Phylogenetic analyses of the 16S rRNA gene located the strain within cluster XI of the lineage encompassing the genus Clostridium and related genera (sensu Collins et al., 1994), in the bacterial domain. On the basis of 16S rDNA sequence comparisons and physiological and biochemical characteristics, it is proposed that the isolate should be described as a novel genus, namely Caminicella gen. nov., of which Caminicella sporogenes sp. nov. is the type species. The type strain is AM1114T (= DSM 14501T = CIP 107141T).

Vertical and temporal variations of particle fluxes in the deep tropical atlantic

Results from the study of particle samples collected during two years of sediment trapping experiments at three depths (2000, 200, 10 m above the bottom) in the oligotrophic Cape Verde abyssal plain (4600 m depth) are reported in this paper. Hydrodynamical and sediment data are assessed in order to ascertain their influence on the carbon budget in the deep-sea. The currents affected by tidal, inertial and longer time-scale oscillations (20–30 and 100–120 days) were sufficiently weak (maximum ⩽14 cm s-1) that trap collection was probably unbiased. The average daily flux estimated at 35.2 mg m-2 d-1 at 2000 m a.b. decreased at 28.8 mg m-2 d-1 at 200 m a.b. Organic carbon, nitrogen and carbonate carbon fluxes decreased between these two depths, suggesting organic carbon oxidation and carbonate dissolution during descent or different sources of particles. At 10 m a.b., the total particle flux (41.3 mg m-2 d-1) increased due to near bottom sediment resuspension. The current orientation explains more resuspension recorded in the first data set. A clear seasonal signal was not observed in this study. However, spectral analysis of the data showed a monthly variation, which might have been due to the reproductive cycle of several planktonic species or some hydrodynamical effect. The degree of correlation between fluxes at 2000 and 200 m a.b. suggests that the largest particles sank at rates equal to or greater than 180 m d-1. At 4600 m depth, 0.3% of the surface primary production reached the deep-sea floor. Estimation of the carbon budget in the bioturbated sediment indicated that only 2% of the organic matter carried by the downward flux was buried in the sediment.

A novel mcl-PHA produced on coprah oil by Pseudomonas guezennei biovar. tikehau, isolated from a "kopara" mat of French Polynesia.

Pseudomonas guezennei biovar. tikehau was isolated from a microbial mat on the atoll of Tikehau in French Polynesia, and is able to synthesize medium chain length poly-beta-hydroxyalkanaote copolymers when grown on coprah oil. A two-step cultivation process was used and the biosynthesis of PHAs was followed along 52h by regular culture sampling. The polyester was purified from freeze-dried cells and analysed by nuclear magnetic resonance (NMR), Fourier transform infra red (FTIR), and gas chromatography mass spectrometries. The copolyester produced by P. guezennei biovar. tikehau from coprah oil mainly consisted of saturated monomers, i.e. 3-hydroxyoctanoate (3HO) and 3-hydroxydecanoate (3HD), and the monomeric composition of the polyester did not change during the fermentation process. However, yield of PHAs production varied from 4% of the cellular dry weight (CDW) to 63% obtained after 36h. Scan electron microscopy was used to study the morphology and organization of PHAs granules within the cells and revealed the presence of several granules occupying almost the entire cell volume.

Acquisition of epibiotic bacteria along the life cycle of the hydrothermal shrimp Rimicaris exoculata

The caridean shrimp Rimicaris exoculata dominates the fauna at several Mid-Atlantic Ridge hydrothermal vent sites. This shrimp has an enlarged gill chamber, harboring a dense ectosymbiotic community of chemoautotrophic bacteria associated with mineral oxide deposits. Until now, their acquisition is not fully understood. At three hydrothermal vent sites, we analyzed the epibionts diversity at different moult stages and also in the first stages of the shrimp life (eggs, hatched eggs (with larvae) and juveniles). Hatched eggs associated with young larvae were collected for the first time directly from gravid females at the Logachev vent site during the Serpentine cruise. An approach using 16S rRNA clone libraries, scanning and transmission electron microscopy, and fluorescent in situ hybridization was used. Molecular results and microscope observations indicated a switch in the composition of the bacterial community between early R. exoculata life cycle stage (egg libraries dominated by the Gammaproteobacteria) and later stages (juvenile/adult libraries dominated by the Epsilonproteobacteria). We hypothesized that the epibiotic phylotype composition could vary according to the life stage of the shrimp. Our results confirmed the occurrence of a symbiosis with Gammaproteobacteria and Epsilonproteobacteria, but more complex than previously assumed. We revealed the presence of active type-I methanotrophic bacteria colonizing the cephalothorax of shrimps from the Rainbow site. They were also present on the eggs from the Logachev site. This could be the first ‘epibiotic’ association between methanotrophic bacteria and hydrothermal vent crustacean. We discuss possible transmission pathways for epibionts linked to the shrimp life cycle.

Near-bottom biological and mineral particle flux in the Lucky Strike hydrothermal vent area (Mid-Atlantic Ridge)

Abstract To provide information about the export and the distribution of hydrothermal material to the deep ocean, two sediment traps with current-meters were moored on the Lucky Strike segment of the Azores Triple Junction (Mid-Atlantic Ridge). The results of a 25-day experiment with a single trap deployed 1.5 m from a chimney (2 m above the bottom) are used as a reference for the composition of particles produced by the vent. A 392-day experiment with a time-series sediment trap positioned 500 m from the Lucky Strike vents (17 m a.b.) showed seasonal variations in the particulate flux and in its composition. Particles sampled by the trap close to the chimney (264.3 mg m −2 day −1 ) were characterised by a high concentration of sulphur (10.8%) and barium (3.19%), and a low C/N ratio (5.5). From the current data recorded at the same time, we estimate that this small trap was under vent influence for about 10% of the experiment duration. The calculated mean particle flux obtained with the multisample sediment trap 500 m away (7.7 mg m −2 day −1 ) was among the lowest recorded in the Atlantic Ocean. This situation may be explained by a very low primary production in the Azores region. No significant influence of the Lucky Strike vent particles was recorded in this trap although near bottom currents were regularly favourable to transport particles towards it. No major effect was observed on the trap efficiency by variations of the hydrodynamic conditions during this experiment. Particles in the trap included bivalve larval shells. A comparison between their hinge structure and that of postlarvae of the mytilid species found on these vents suggests a non-hydrothermal origin for the larvae in the trap.

Particle flux in the Rainbow hydrothermal vent field (Mid-Atlantic Ridge) : Dynamics, mineral and biological composition

In order to provide information about the export and the distribution of hydrothermal particulate material to the surrounding deep ocean, four moorings were deployed in the vicinity of the hydrothermal Rainbow vent e eld (Mid-Atlantic Ridge, 36° 14 9N, 2250 m depth). The e rst mooring was a sediment trap with a current meter deployed at 2 m from a chimney of the Rainbow vent e eld and 1.5 m above the bottom (a.b.) for 16 days. It represented the reference for the initial composition of particles produced by the vent. The total mean mass particle e ux (6.9 g m 2 2 d 2 1 ) was distinctly higher than the e ux measured at the shallower hydrothermal vents on the MAR segment. This particulate e ux showed a high temporal variation at the scale of a few days and was characterized by a high concentration of sulphur (17.2%) and copper (3.5%) and a very low concentration of organic carbon (0.14%). Several hundred bivalve larvae belonging to the hydrothermal mytilid Bathymodio- lus azoricus were collected in this trap at the beginning of the experiment. The density of larvae decreased strongly at the end, indicating a patchiness distribution or a discontinuous reproduction of this species. The other three moorings, including sediment traps, current-meters and thermistor chains, were deployed for 304 days at different distances and altitudes from the Rainbow vent e eld. The mean speed of the current in the rift valley was low (6 cm s 2 1 ) and was oriented toward the north. The total mean particle mass e ux measured with the e ve sediment traps varied little, from 10.6 to 25.0 mg m m 2 2 d 2 1 , and displayed temporal variations which are typical of deep-sea environ- ments with seasonal changes in the overlying production. However, in the trap at 500 m from the vents 150 m a.b., the presence of the hydrothermal plume can be observed: the sulphur, iron and copper concentrations of particles were signie cantly higher compared to the particles sampled in the pelagic reference trap. The plume composition was about 50% hydrothermal particles and 50% pelagic particles and its upper limit reached 300 m a.b. at this distance. In the traps at 1000 m from the vents, the elemental composition of particles was similar to the pelagic particles and we assume that these traps were not in the plume during the experiment. The zooplankton obtained in the long-term trap samples revealed high density variations in relation to the distance from the vent site. The nutrient enrichment around the hydrothermal area and the abundance of free living bacteria explain these variations in zooplankton density.

[27] Extracellular polymers of microbial communities colonizing ancient limestone monuments

Publisher Summary This chapter discusses the extracellular polymers of microbial communities colonizing ancient limestone monuments. Biofilms are layered microbial communities growing on inert and livingsurfaces in a variety of terrestrial and aquatic environments, including submerged artificial substrata, invertebrate teguments, sediments, soils, and rock surfaces. The exopolymers, mainly composed of polysaccharides, are an important component of such biofilm communities and their functional roles in terms of attachment, nutrient absorption, and protection against desiccation and antimicrobial agents. Given the anionic substituents that these compounds may have, they can interact actively with dissolved ions in aqueous environments and with framework elements in mineral matrices. The implications of such interactions among exopolysaccharides (EPS) and minerals may also include cation mobilization in soils, solubilization of toxic metals, and the dissolution of minerals. On other hand, studies carried out in Mayan archaeological sites (Yucatan, Mexico) have shown that thick microbial biofilms dominated by cyanobacterial populations contributed to the biodegradation of these buildings by supporting growth of organic acid-producing microorganisms and through active boring. These microbial exopolymers may contribute directly to the deterioration processes by interacting through their polysaccharide fraction with metal cations, which could lead to the complexation of soluble calcium, sequestering it from the limestone matrix. This chapter describes procedures to extract and characterize the polysaccharidic fraction of naturally occurring microbial exopolymers associated with epilithic biofilms.