Philippe Cuny

Enhanced biodegradation of phenanthrene by a marine bacterium in presence of a synthetic surfactant.

The biodegradation of phenanthrene by the marine strain Sphingomonas sp. 2MPII (DSMZ 11572) was enhanced by the solubilizating properties of the nonionic surfactant Tween 80. After 197u2003h of incubation, 85u2003±u20034% of the initial amount of phenanthrene (0.4u2003gu2003l−1) was biodegraded in presence of Tween 80 (0.5u2003gu2003l−1) as opposed to 52u2003±u20035% without this synthetic surfactant. These results confirm that the activity of the strain 2MPII is limited by the bioavailability of the polycyclic aromatic hydrocarbon (PAH) substrate in the aqueous phase. Tween 80 appears to be efficient in increasing the bioavailability of hydrophobic compounds such as PAHs.

Isolation of alkane‐degrading bacteria from deep‐sea Mediterranean sediments

Aims:u2002 To isolate and identify alkane‐degrading bacteria from deep‐sea superficial sediments sampled at a north‐western Mediterranean station.

Influence of Chironomus riparius (Diptera, Chironomidae) and Tubifex tubifex (Annelida, Oligochaeta) on oxygen uptake by sediments. Consequences of uranium contamination.

The diffusive oxygen uptake (DOU) of sediments inhabited by Chironomus riparius and Tubifex tubifex was investigated using a planar oxygen optode device, and complemented by measurements of bioturbation activity. Additional experiments were performed within contaminated sediments to assess the impact of uranium on these processes. After 72h, the two invertebrate species significantly increased the DOU of sediments (13-14%), and no temporal variation occurred afterwards. Within contaminated sediments, it was already 24% higher before the introduction of the organisms, suggesting that uranium modified the sediment biogeochemistry. Although the two species firstly reacted by avoidance of contaminated sediment, they finally colonized it. Their bioturbation activity was reduced but, for T. tubifex, it remained sufficient to induce a release of uranium to the water column and an increase of the DOU (53%). These results highlight the necessity of further investigations to take into account the interactions between bioturbation, microbial metabolism and pollutants.

Hydrostatic pressure affects membrane and storage lipid compositions of the piezotolerant hydrocarbon-degrading Marinobacter hydrocarbonoclasticus strain #5

A new piezotolerant alkane-degrading bacterium (Marinobacter hydrocarbonoclasticus strain #5) was isolated from deep (3475 m) Mediterranean seawater and grown at atmospheric pressure (0.1 MPa) and at 35 MPa with hexadecane as sole source of carbon and energy. Modification of the hydrostatic pressure influenced neither the growth rate nor the amount of degraded hexadecane (approximately 90%) during 13 days of incubation. However, the lipid composition of the cells sharply differed under both pressure conditions. At 0.1 MPa, M. hydrocarbonoclasticus #5 biosynthesized large amounts ( approximately 62% of the total cellular lipids) of hexadecane-derived wax esters (WEs), which accumulated in the cells under the form of individual lipid bodies. Intracellular WEs were also synthesized at 35 MPa, but their proportion was half that at 0.1 MPa. This lower WE content at high pressure was balanced by an increase in the total cellular phospholipid content. The chemical composition of WEs formed under both pressure conditions also strongly differed. Saturated WEs were preferentially formed at 0.1 MPa whereas diunsaturated WEs dominated at 35 MPa. This increase of the unsaturation ratio of WEs resembled the one classically observed for bacterial membrane lipid homeostasis. Remarkably, the unsaturation ratio of membrane fatty acids of M. hydrocarbonoclasticus grown at 35 MPa was only slightly higher than at 0.1 MPa. Overall, the results suggest that intracellular WEs and phospholipids play complementary roles in the physiological adaptation of strain #5 to different hydrostatic pressures.

Characterization of specificity of bacterial community structure within the burrow environment of the marine polychaete Hediste (Nereis) diversicolor

Bioturbation is known to stimulate microbial communities, especially in macrofaunal burrows where the abundance and activities of bacteria are increased. Until now, these microbial communities have been poorly characterized and an important ecological question remains: do burrow walls harbor similar or specific communities compared with anoxic and surface sediments? The bacterial community structure of coastal sediments inhabited by the polychaete worm Hediste diversicolor was investigated. Surface, burrow wall and anoxic sediments were collected at the Carteau beach (Gulf of Fos, Mediterranean Sea). Bacterial diversity was determined by analyzing small subunit ribosomal RNA (16S rRNA) sequences from three clone libraries (168, 179 and 129 sequences for the surface, burrow wall and anoxic sediments, respectively). Libraries revealed 306 different operational taxonomic units (OTUs) belonging to at least 15 bacterial phyla. Bioinformatic analyses and comparisons between the three clone libraries showed that the burrow walls harbored a specific bacterial community structure which differed from the surface and anoxic environments. More similarities were nevertheless found with the surface assemblage. Inside the burrow walls, the bacterial community was characterized by high biodiversity, which probably results from the biogeochemical heterogeneity of the burrow system.

Luminous bacteria in the deep-sea waters near the ANTARES underwater neutrino telescope (Mediterranean Sea)

Marine luminous deep-sea bacteria may represent a potential source of signal perturbation for the ANTARES neutrino telescope installed between 2000 and 2475 m depth in the Mediterranean Sea. Using the CARD-FISH method, we have estimated the relative abundances of total prokaryotes of Bacteria, γ -proteobacteria and Vibrinoceae (domain, class and family affiliation of marine luminous bacteria, respectively) through the water column close to the ANTARES site. At 2200 m depth, Vibrionaceae appeared to be far from negligible, representing 40% of γ -proteobacteria, 25% of Bacteria and 9% of the total DAPI-stained cells, while Bacteria and Archaea represented 35% each. Furthermore, during a high luminous background period detected by the neutrino telescope, we isolated, from a 2200 m depth sample, a piezophilic luminous bacterium, phylogenetically determined as Photobacterium phosphoreum strain ANT-2200. We have used this strain to investigate the effect of hydrostatic pressure on bioluminescence by developing a new high-pressure apparatus. First assays showed that the bioluminescence intensity of Photobacterium phosphoreum strain ANT-2200 was 5 times higher at 22 MPa than at 0.1 MPa (atmospheric pressure).

Phenanthrene degradation, emulsification and surface tension activities of a pseudomonas putida strain isolated from a coastal oil contaminated microbial mat

Abstract Kinetics of phenanthrene degradation, emulsification and surface tension activities of this hydrocarbon upon degradation by a Pseudomonas putida (COB 3-2) isolated from a coastal microbial mat were investigated. After 27 days of incubation at 20°C, 71.4±3.4 % of the initial phenanthrene amount (0.4 g l-1) were biodegraded. Observation of both tension-active and emulsifying activities indicated that biosurfactants, probably rhamnolipids, are generated. The high phenanthrene degrading capacity and biosurfactant production potential of this newly isolated P. putida strain may contribute positively to oil bioremediation processes within the microbial mat.

Oxygen Distribution Heterogeneity Related to Bioturbation Quantified by Planar Optode Imaging

Oxygen plays a key role in benthic microbial ecology. Until recently, oxygen concentration in sediments was measured with oxygen microsensors along a vertical profile (one dimension) from the surface until a few centimeters into the sediment. With this approach, however, it is a tedious job to describe or overcome the heterogeneity of oxygen distribution in environments such as bioturbated environments. Recently, a new technique has been introduced that allows the investigation of two-dimensional oxygen distribution and dynamics at a high resolution in the upper sediment column. This non-destructive technique takes advantage of an oxygen-quenchable fluorophore, which is cast into a thin sheet, the planar optode. The latter may be introduced in sediments and is used in situ or in laboratory experimentation, coupled with an optical system allowing the oxygen quantification. Oxygen optodes were used in experimentation dedicated to the study of oxygen heterogeneity induced by macrofaunal bioturbation. Oxygen images of sediments inhabited by a biodiffusor, the gastropod Cyclope neritea, and two gallery diffusors, the annelids Nereis virens and Nereis diversicolor, were used to compare the impact of these organisms on oxygen distribution in sediments. Diffusive oxygen flux and a heterogeneity index were quantified based on oxygen images. Results showed that all species increased oxygen distribution heterogeneity, and that this heterogeneity increased with increasing total diffusive fluxes.

Hydrocarbon Degradation in Coastal Muddy Areas and Anoxic Ecosystems (DHYVA Project): Role of Bacterial Mechanisms and Bioturbation Effects on the Biodisponibility of Organic Pollutants

Muddy areas and more or less coastal anoxic zones play a key role in maintaining the integrity of estuarine and coastal ecosystems. By their localization, these areas are frequently exposed to pollutant damage, such as oil spills or accidental events, and accumulate various pollutants released by continental hydrosystems. Due to their composition (fine silt sediments), actual remediation techniques are not adapted. These artificial compounds accumulate in different sites, constituting “pollutant reservoirs” that are threats for the ecosystem as well as for human health. Microorganisms play a key role in hydrocarbon degradation. However, most of our knowledge has been obtained by studies on isolated bacterial strains. In addition, bacterial cooperation within different microbial groups has been demonstrated for the degradation of complex hydrocarbon mixtures. Silt sediments are located at the oxic/anoxic interface where various bacterial metabolisms coexist and follow one another through the function of the tides. Moreover, burrowing organisms can influence the bacterial metabolisms by making the oxygen penetration easier. It thus seems judicious to tackle the problem of hydrocarbon degradation in a global way, trying to understand how bacterial metabolisms interact in the degradation of the pollutants and to estimate the bioturbation effects of these activities. This is the main objective of the project DHYVA (Degradation des HYdrocarbures dans les VAsieres), with a special focus on anaerobic degradation mechanisms, about which we have limited knowledge.

Assessment of oil weathering and impact in mangrove ecosystem: PRISME Experiment.

Abstract 2017-410 Mangroves are among the most sensitive marine ecosystems to oil pollution due both to the sensitivity of mangroves species and to the high persistence of hydrocarbons in these env...