Dominique Fontvieille

Taxon-specific and seasonal variations in flagellates grazing on heterotrophic bacteria in the oligotrophic Lake Annecy – importance of mixotrophy

We investigated the taxonomic composition of flagellate assemblages and taxon-specific bacterial grazing rates of heterotrophic and mixotrophic flagellates in the oligotrophic Lake Annecy (France). The comparison of bacterial grazing rates to bacterial production demonstrated a high transfer efficiency from the bacterial compartment up to flagellates. Per capita grazing rates ranged from 1.2x10(3) to 5.1x10(6) bacteria l(-1) h(-1) for heterotrophic flagellates, and from 4.8x10(6) to 6.8x10(7) bacteria l(-1) h(-1) for mixotrophic flagellates. The main bacterial grazers were Katablepharis within heterotrophic flagellates and Dinobryon within mixotrophic flagellates. Our results show that bacterial ingestion by a given flagellate taxon changed seasonally and could vary up to 30-fold. We also provide evidence that mixotrophic flagellates represent an important link in the flux of materials through planktonic food webs in Lake Annecy, suggesting that the introduction of mixotrophs within functional groups could improve our understanding of carbon flux pathways.

Distribution of Dissolved Organic Carbon and Bacteria at the Interface between the Rhône River and Its Alluvial Aquifer

To understand the efficiency of interstitial habitats in the elimination of organic matter as it moves from surface water to groundwater (bank filtration), we studied spatial and temporal variations of sediment organic matter concentration, biodegradable (BDOC) and refractory (RDOC) fractions of the dissolved organic carbon, bacterial abundances, and microbial enzymatic activity in the first metre of sediment of the Rhône River immediately downstream of a large city. The study area was fed most of the year by the surface water inflow (downwelling area), because of groundwater pumping wells located ∼ 80 m from the river. Decreasing gradients from surface water to deep sediments and from the river to the shore were observed in most of the cases for the four variables. The decrease in RDOC concentrations did not vary seasonally (this decrease is probably due to physical process, such as adsorption on fine mineral particles), whereas decreases in BDOC concentrations only occurred when microbial enzymatic activities were high; BDOC is rapidly assimilated by microbial communities. Physical and biological processes together make this first metre of sediment an efficient filter for organic matter.

Correlating the structure and composition of ionic liquids with their toxicity on Vibrio fischeri: A systematic study

A systematic screening of the toxicity of ionic liquids (IL) towards Vibrio fischeri, a bioluminescent marine bacteria generally used in ecotoxicological bioassays, was carried out. The objectives of this work were to find hydrophilic or hydrophobic low toxicity IL and to investigate structure-toxicity relationship of IL. Toxicity of 54 IL to V. fischeri have been measured, some referring to new IL based on quinuclidinol or tropinol and some to generic IL (i.e., imidazolium, pyridinium, pyrrolidinium or piperidinium). For 47 of them, toxicity values have not been reported elsewhere. Water-soluble IL containing hydrophilic anions halide, thiocyanate, dicyanamide, trifluoromethansulfonate were studied. Some IL were found to exhibit very low toxicity towards V. fisheri. Hydrophobic IL based on bis(trifluoromethanesulfonyl)imide, tetrafluoroborate tetraphenylborate and tetracyanoborate were also studied. Toxicity was measured in a consistent way starting from aqueous solutions saturated with IL. The least toxic hydrophobic IL found in this study was [EMIM][B(CN)(4)]. A multifactorial analysis was found to be convenient for finding relevant structure parameters influencing the toxicity of IL. From this analysis, the planarity of the cation ring appeared to be a relevant parameter. Finally, good linear correlations were found when toxicity of IL was plotted either against the number of aliphatic carbons surrounding a pyridinium cation or the total number of carbons of a cation.

Experimental degradation of plant materials in Hudson river sediments

We examined photopigment degradation and transformation in sediment microcosms that received different detrital source materials (planktonic, littoral, terrestrial) in the presence or absence of amphidpods (Gammarus sp.). Additions of realistic quantities of particulate organic matter resulted in detectable changes in pigment concentration and composition despite insignificant changes in total organic matter. The transformation of chlorophyll a to total phaeophorbide was significantly higher in all high quality (high nitrogen) detritus treatments containing amphipods. The highest production of phaeophorbide was in the higher quality detritus (blue-green algae, Anabaena cylindrica, and macrophyte, Vallisneria americana) when compared to red maple (Acer rubrum). Phaeophytin formation was not related to amphipod grazing and thus may be determined more by microbial heterotrophic processes. The degradation product of the carotenoid lutein, lutein 5,6 expoxide, was formed in all treatments. Phaeopigment composition can be used to infer differences in heterotrophic activity and will help in the interpretation of photopigment distribution in field samples.

Molecular diversity and high virulence of Legionella pneumophila strains isolated from biofilms developed within a warm spring of a thermal spa

BackgroundSeveral cases of legionellosis have been diagnosed in the same French thermal spa in 1986, 1994 and 1997. L. pneumophila serogroup 1 (Lp1) strains have been isolated from several patients, but the source of contamination was not identified despite the presence of different Lp1 in water samples of the three natural springs feeding the spa at this period.ResultsOur strategy was to investigate L. pneumophila (Lp) strains from natural biofilms developed in a sulphur-rich warm spring of this contaminated site. Biofilm analysis revealed the presence of three Lp serogroups (Lp1, Lp10 and Lp12). Surprisingly, Lp10 and Lp12 were not reported in the previous described studies from water samples. Besides, the new seven Lp1 we isolated exhibit a high molecular diversity and have been differentiated in five classes according to their DNA genome patterns obtained by PFGE and mip sequences. It must be noted that these DNA patterns are original and unknown in databases. Interestingly, the 27 Lp environmental strains we isolated display a higher cytotoxicity and virulence towards the amoeba Acanthamoeba castellanii than those of known Lp1 epidemic strains.ConclusionThe characteristics of Legionella pneumophila Lp1 strains isolated from the warm spring are in agreement with their presence in biofilms and their probable long-term persistence in this ecosystem.

Comparison of solutes, nutrients, and bacteria inputs from two types of groundwater to the Rhône river during an artificial drought

Solute, nutrient and bacterial inputs to the River Rhône from the interstitial habitat of a gravel bar and the floodplain aquifer were investigated during an artificial drought. Eight springs were investigated: four groundwater-fed springs in the floodplain, located at the bottom of the bank; and four interstitial-fed springs located at the downstream end of a gravel bar. During this period, the inflows of groundwater to the river represented an average input of 0.77 mg l−1 of nitrogen (of which 93.3% were nitrates), 0.0187 mg l−1 of total phosphorus (of which 42.2% was orthophosphate), 3.56 mg l−1 of silica, 2.315 ± 0.703 mg l−1 of dissolved organic carbon (DOC, of which 47% was biodegradable) and 7.3 × 104 ± 3.7 × 104 bacteria per ml (of which 8.8% were active). Silica, DOC, biodegradable DOC, and bacteria concentrations displayed temporal variations during the study, which seem to be linked to the biological activity of the groundwater biofilm. There was a strong heterogeneity between the two types of groundwater that flow to the river: concentrations of calcium and alkalinity were higher in bank springs than in gravel bars springs. In these latters, sulfate, sodium, nitrogen, phosphorus were significantly higher.

Impact of a flood event on the biogeochemical behaviour of a mesotrophic alpine lake : Lake Bourget (Savoy)

A flood event which occurred during the onset of thermal stratification and of algal growth (March 1996) was studied in mesotrophic Lake Bourget (France). Both physical and biogeoehemical processes occurring during this episode were assessed. The dominant effect was a decrease of nutrient concentrations along the river—lake ecotone. This phenomenon seemed mainly linked to biological factors: stimulation of the spring algal and bacterial growth. After the flood, the algae aggregated with allochthonous particles brought by the river and were rapidly eliminated by sedimentation. The effect of this early spring flood, seemed spatially restricted and rather neutral as regards lake water quality. In the lake region crossed by the river plume, the overall effect after the flood was a decrease of P available for the phytoplankton. In the open water, the P concentration was probably not modified by the load supplied by the flood.

Toxicological consequences of extracting KNbO3 and BaTiO3 nanoparticles from water using ionic liquids

Hydrophobic room-temperature ionic liquids were used to remove KNbO3 and BaTiO3 nanoparticles from water at 25 °C. A very good extraction efficiency was obtained with distribution coefficients as high as 500. After extraction, toxicity of the aqueous phase containing residual amounts of nanoparticles and ionic liquids was assessed using Vibrio fischeri. A preliminary investigation of the toxicity mechanism was carried out with propidium iodide tests. A key result is that the simultaneous presence of a small amount of nanoparticles and ionic liquid in water can result in adverse toxicological effects compared to aqueous solutions containing solely nanoparticles or ionic liquids.

Changes in biologically controlled carbon fluxes in a small stream following continuous supply of excess organic load

The consequences of a constant supply of organic load from a pigsty to a small 2nd order stream are analysed through simultaneous consideration of amount of carbon stored in benthic biomass and of main biologically controlled carbon fluxes.The results show that the allochthonous load induced a general increase in all fluxes and therefore stimulated processes of carbon elimination from the receiving system.The increase of biologically controlled fluxes was due to qualitative changes of populations toward specialization for an optimal use of the newly supplied organic substrates. This was especially evident in this stream for macro-invertebrate biomass production and for insect emergence.Effects of trophic pollution ranged from drastic modifications near the input of the pig waste to a place where the additional supply of organic substrate increased the numbers of individuals of macroinvertebrate populations without any change in their specific diversity.Variations of CO2 production appeared to be more related to biomass of microbial populations in the downstream station and to macroinvertebrates in the upstream station.Although the allochthonous load caused significant increases in several processes involved in its own elimination, the magnitude of these increases was small compared to the influx of organic carbon from upstream and from the pigsty.