Daniel Delille

Marine bacterioplankton at the Weddell Sea ice edge, distribution of psychrophilic and psychrotrophic populations

In the eastern Weddell Sea on several transects from ice-covered, through ice melt, to open-ocean stations, total and heterotrophic bacteria were estimated to document an enhanced bacteriological biomass expected near the ice edge. The highest numbers of bacteria were found in melted ice cores, with 4.2·103 CFU ml-1 and 1.1·107 Cells ml-1 Although brine from pore water samples average more than one order of magnitude less cells per ml, the highest bacterial production, 2.2·107 cells 1-1 day-1, was recorded in brine samples. All quantitatively studied bacterial parameters were lower under the ice than in the ice samples but there were no clear vertical gradients in the water column. In the studied spring situation, sea ice occurrence seems to play only a minor role in the general distribution of the seawater bacterioplankton. The bacterial community structure was investigated by carrying out 29 morphological and biochemical tests on 118 isolated strains. The bacterial communities inhabiting Antarctic pack ice differ from those found in underlying seawater. Although non fermentative Gram-negative rods were always dominant in seawater, Vibrio sp. represented more than 25% of the strains isolated from some ice samples. The results clearly indicated that a large majority of the bacteria isolated from seawater must be considered psychrotrophic but that truly psychrophilic strains occurred in melted ice and brine samples.

Did psychrophilic enzymes really win the challenge

Abstract. Organisms living in permanently cold environments, which actually represent the greatest proportion of our planet, display at low temperatures metabolic fluxes comparable to those exhibited by mesophilic organisms at moderate temperatures. They produce cold-evolved enzymes partially able to cope with the reduction in chemical reaction rates and the increased viscosity of the medium induced by low temperatures. In most cases, the adaptation is achieved through a reduction in the activation energy, leading to a high catalytic efficiency, which possibly originates from an increased flexibility of either a selected area of or the overall protein structure. This enhanced plasticity seems in return to be responsible for the weak thermal stability of cold enzymes. These particular properties render cold enzymes particularly useful in investigating the possible relationships existing between stability, flexibility, and specific activity and make them potentially unrivaled for numerous biotechnological tasks. In most cases, however, the adaptation appears to be far from being fully achieved.

Effectiveness of Bioremediation of Crude Oil Contaminated Subantarctic Intertidal Sediment: The Microbial Response

A field study was initiated in February 1996 in a remote sandy beach of The Grande Terre (Kerguelen Archipelago, 69° 42° E, 49° 19° S) with the objective of determining the long-term effects of some bioremediation agents on the biodegradation rate and the toxicity of oil residues under severe subantarctic conditions. A series of 10 experimental plots were settled firmly into sediment. Each plot received 2L of Arabian light crude oil and some of them were treated with bioremediation agents: slow release fertilizer Inipol EAP-22 (Elf Atochem) or fish composts. Plots were sampled on a regular basis over a 3-year period. A two-order of magnitude increase of saprophytic and hydrocarbon-utilizing microorganisms occurred during the first month of the experiment in all treated enclosures, but no clear differences appeared between the plots. Very high microbial populations were present during the experiment. Biodegradation within treated spots was faster than within the untreated ones and appeared almost complete after 6 months as indicated by the degradation index of aliphatic hydrocarbons within all plots. The analysis of interstitial water collected below the oily residues presented no toxicity. However, a high toxicity signal, using Microtox solid phase, appeared for all oiled sand samples with a noticeable reduction with time even if the toxicity signal remained present and strong after 311 days of oil exposition. As a conclusion, it is clear that the microbial response was rapid and efficient in spite of the severe weather conditions, and the rate of degradation was improved in presence of bioremediation agents. However, the remaining residues had a relatively high toxicity.

Seasonal changes of pCO2 over a subantarctic Macrocystis kelp bed

Abstract The partial pressure of carbon dioxide (pCO2), calculated from pH and total alkalinity measurements, was monitored together with chlorophyll a and bacterioplankton biomass in shallow coastal water located inside and outside a giant kelp bed (Macrocystis pyrifera) situated in the Kerguelen Archipelago, Southern Ocean. In spite of large changes over a short time-scale, pCO2 variations over the year are large and exhibit a seasonal pattern in which the different stages of the annual biological turnover are well marked. The overall pattern of pCO2 variations is related to biological activity (development of both photosynthesis and respiration) during almost the whole year. However, physical and thermodynamical constraints exert a strong influence on pCO2 at meso time-scale (10 days) and/or when biological activity is weak. Macrocystis acts to maintain pCO2 below saturation almost the whole year and large undersaturations (pCO2 as low as 20 μatm) were observed within the kelp bed. Furthermore, primary production of Macrocystis covers a period of 8 ∼ 9 months a year from winter to late summer and the kelp bed seems to favour the spring phytoplanktonic bloom. The buffer factor β indicates that, outside the kelp bed, inorganic carbon dynamics are mainly influenced by air-sea exchange and photosynthesis without calcification. Inside the kelp bed, β suggests calcification by the epiphytic community.

Short-term variations of bacterioplankton in Antarctic zone: Terre Adélie area

Previous studies on Antarctic seawater have demonstrated the presence of significant numbers of bacteria, but their in situ activity has not been demonstrated. In order to demonstrate this hypothetical activity, a scheduled survey was conducted from January to February 1986 in a coastal area of Adelie Land. Seawater samples were collected in a selected station every day or every hour during a 17 hour period. Bacterial communities in each sample were studied by measuring direct and viable counts, frequency of dividing cells estimation, taxonomic analysis, and heterotrophic potential. Complementary studies used batch cultures with artificial nutrient supplements. The results clearly suggest a strong potential activity of the natural Antarctic bacterial microflora.

Fate and Effects of Dispersed Crude Oil Under Icy Conditions Simulated in Mesocosms

The fate of the chemically dispersed crude oil Forties, the effects on natural phytoplankton and bacteria and the hydrocarbon biodegradation were studied in mesocosms during a two-week period in winter. Five double-walled stainless steel tanks (3 m height; 3·5 m3) were used. Each tank was equipped with a cooling system maintaining entrapped seawater below zero (−1·6 ± 0·2°C) and under an ice coverage, simulating winter conditions prevailing in boreal/sub-boreal environments. A flow-through cascade set-up between three tanks simulated the progressive dilution of the oil in the water mass. A total oil concentration of 7·5 mg liter−1 was measured in the water column of the oiled cascading tanks, four days after the addition of 435 g (nominal concentration of 124 mg liter−1) of dispersed crude oil. At this time, most of the oil (> 90%) initially introduced into mesocosms had escaped the water column, mainly toward the surface. A non-negligible portion of the oil (5·7%) was settling during the course of the experiment. The low efficiency of the dispersant mixture used and the oil settling seemed to be due to the very low seawater temperature tested here. In the first days following the oil addition, a slight decline of viable heterotrophic bacteria was noted in the tanks, and then the oil improved the heterotrophic activity by the end of the experiment. The marked increase of both density and proportion of oil-degrading bacteria observed two days after the oil addition gave evidence of the potential capability of the indigenous bacterial community to adapt to an oil spill event. However, under such extreme icy conditions, the biodegradation of the dispersed oil was reduced and only the aliphatic hydrocarbon fraction, mainly recovered as dispersed oil droplets, was slightly degraded. The aromata hydrocarbon fraction, on the other hand, essentially recovered as dissolved/colloidal compounds (< 0·7 μm), was not altered after two weeks. Oil biodegradation in the material collected in sediment traps progressed more rapidly than in the water column. At the end of the experiment, about 1–2 mg liter−1 of oil remained in the water column and still induced a chl-a inhibition, but no significant change of the specific composition of the phytoplankton was noted, microflagellates remaining dominant throughout the experiment (40·5–76% in number).

Effects of temperature and fertilization on total vs. active bacterial communities exposed to crude and diesel oil pollution in NW Mediterranean Sea

The dynamics of total and active microbial communities were studied in seawater microcosms amended with crude or diesel oil at different temperatures (25, 10 and 4 degrees C) in the presence/absence of organic fertilization (Inipol EAP 22). Total and hydrocarbon-degrading microbes were enumerated by fluorescence microscopy and Most Probable Number (MPN) method, respectively. Total (16S rDNA-based) vs. active (16S rRNA) bacterial community structure was monitored by Capillary-Electrophoresis Single Strand Conformation Polymorphism (CE-SSCP) fingerprinting. Hydrocarbons were analyzed after 12 weeks of incubation by gas chromatography-mass spectrometry. Total and hydrocarbon-degrading microbial counts were highly influenced by fertilization while no important differences were observed between temperatures. Higher biodegradation levels were observed in fertilized microcosms. Temperature and fertilization induced changes in structure of total bacterial communities. However, fertilization showed a more important effect on active bacterial structure. The calculation of Simpsons diversity index showed similar trends among temperatures whereas fertilization reduced diversity index of both total and active bacterial communities.

Effects of nutrient and temperature on degradation of petroleum hydrocarbons in sub-Antarctic coastal seawater

In an attempt to evaluate the potential of petroleum bioremediation at high latitudes environments, microcosm studies using Antarctic coastal seawater contaminated with diesel or crude oil were conducted in Kerguelen Archipelago (49°22′S, 70°12′E). Microcosms were incubated at three different temperatures (4, 10 and 20°C). During experiments, changes observed in microbial assemblages (total direct count, heterotrophic cultivable microorganisms and hydrocarbon-degrading microorganisms) were generally similar for all incubation temperatures, but chemical data showed only some slight changes in biodegradation indices [Σ(C12–C20)/Σ(C21–C32) and C17/pristane]. The complete data set provided strong evidence of the presence of indigenous hydrocarbon-degrading bacteria in Antarctic seawater and their high potential for hydrocarbon bioremediation. The rate of oil degradation could be increased by the addition of a commercial fertilizer, but water temperature had little effects on biodegradation efficiency which is in conflict with the typical temperature-related assumption predicting 50% rate reduction when temperature is reduced by 10°C. Global warming of Antarctic seawater should not increase significantly the rate of oil biodegradation in these remote regions.

A perspective on cold enzymes: current knowledge and frequently asked questions

Studies on psychrophilic enzymes to determine the structural features important for cold-activity have attracted increased attention in the last few years. This enhanced interest is due to the attractive properties of such proteins, i.e. a high specific activity and a low thermal stability, and thus, these enzymes constitute a tremendous potential for fundamental research and biotechnological applications. This review examines the impact of low temperatures on life, the diversity of adaptation to counteract these effects and gives an overview of the features proposed to account for low thermal stability and cold-activity, following the chronological order of the catalytic cycle phases. Moreover, we present an overview of recent techniques used in the analysis of the flexibility of a protein structure which is an important concept in cold-adaptation; an overview of biotechnological potential of psychrophilic enzymes and finally, a few frequently asked questions about cold-adaptation and their possible answers.

Biostimulation of Natural Microbial Assemblages in Oil-Amended Vegetated and Desert Sub-Antarctic Soils

A field study was initiated in December 2000 in two selected soils of The Grande Terre (Kerguelen Archipelago) with the objective of determining the long-term effects of fertilizer addition on the biodegradation rate and the toxicity of oil residues under severe sub-Antarctic conditions. Two soils were selected. The first site supports an abundant vegetal cover; the second one was desert soil, devoid of plant material. These two soils were located in the vicinity of the permanent station of Port-aux-Français (69° 42′E; 49° 19′S). A series of five experimental plots (0.75 × 0.75 m) were settled firmly into each of the studied soils. Each plot received 500 mL of diesel or Arabian light crude oil, and some of them were treated with a bioremediation agent: slow-release fertilizer Inipol EAP-22 (Elf Atochem). All the plots were sampled on a regular basis over a 1 year period. Heterotrophic and hydrocarbon-degrading microorganisms increased by two orders of magnitude during the first month of the experimentation in all treated enclosures, but differences appeared between the different plots. The microbial response was improved by bioremediation treatments. However, fertilizer addition had a greater impact on the desert soil when compared to the vegetated one. All chemical indices show a reduction of alkanes and light aromatics. Toxicity results show a high variability between treatments and environmental conditions. As a conclusion, it is clear that the microbial response was rapid and efficient in spite of the severe weather conditions, and the rate of degradation was improved by bioremediation treatments. However, after 1 year of treatment, the signal of a relatively high toxicity of oiled residues remained present in the two studied soils.