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ABSTRACT: Despite the implication of anaerobic soil communities in important functions related to C and N biogeochemical cycles, their responses to pesticides are rarely assessed. This study focused on the impact of alachlor, a chloroacetanilide herbicide, on two agricultural soils differing in their land use (fallow and corn-cultivated) in order to investigate the potential adaptation of anaerobic or facultative anaerobic soil microorganisms from fields with long history of herbicide use. The experiment was performed by developing slurries in anoxic conditions over 47 days. Changes in the community structure assessed through terminal restriction fragment length polymorphism analysis of 16S rRNA genes clearly showed a shift in the bacterial community of the cultivated soil, whereas the modification of the microbial community of the fallow soil was delayed. In addition, the analysis of alachlor degradation capacities of the two anaerobic communities indicated that 99 % of alachlor was removed in anoxic slurries of cultivated soil. Both these results suggested the preexistence of microorganisms in the cultivated soil able to respond promptly to the pesticide exposure. The composition of the anaerobic active community determined by 16S rRNA transcript analysis was mainly composed of strictly anaerobic Clostridia and the facultative anaerobe Bacilli classes. Some genera, described for their role in herbicide biodegradation were active in alachlor-treated slurries, whereas others were no longer detected. Finally, this study highlights, when triggered, the important diversity of the anaerobic community in soil.
Environmental Science and Pollution Research 06/2012; · 2.65 Impact Factor
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ABSTRACT: Since lipids are depleted in 13C relative to proteins and carbohydrates, variations in lipid composition among species and within individuals significantly influence delta13C and may result in misleading ecological interpretations. Whereas lipid extraction before IRMS analysis constitutes a way of stable isotope result lipid-normalisation, such a procedure was given up because of the un-controlled effects of the methods used (i.e., "Bligh & Dyer", Soxhlet, etc.) on delta15N. The aim of this work was to develop a simple, rapid and efficient lipid extraction method allowing for simultaneous C and N stable isotope analysis in the biological soft tissues of aquatic organisms. The goal was to be free from the lipid influence on delta13C values without interfering with delta15N values. For that purpose, the modern automated pressurized liquid extraction technique ASE (accelerated solvent extraction) was selected. Eel muscles representative of a broad range of fat contents were extracted via ASE by using different semi-polar solvents (100% dichloromethane and 80% n-hexane/20% acetone) and by operating at different temperature (ambient temperature and 100 degrees C) and pressure (750 and 1900 psi) conditions. The results were discussed in terms of lipid extraction efficiency as well as delta13C and delta15N variability.
Analytica chimica acta 07/2009; 643(1-2):54-60. · 4.31 Impact Factor
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ABSTRACT: Leachate recirculation allows an increase of moisture content and the enhancement of the anaerobic digestion of wastes in landfill. Since there is no ammonia elimination process in landfill when leachate is recirculated, NH(4) (+) may accumulate. One strategy for NH(4) (+) removal is to treat aerobically the leachate outside the landfill to convert NH(4) (+) into NO(3) (-). When nitrified leachate is recirculated, denitrification should occur in the waste. We have previously shown that wastes have a large capacity to convert nitrate into N(2). Nevertheless, in some cases we observed nitrate reduction without gaseous nitrogen production. Using a stepwise multiple regression models, H(2)S concentration was the unique parameter found to have a negative effect on N(2) production. We then suspected that dissimilatory nitrate reduction to ammonium (DNRA) occurred in the presence of H(2)S. In order to verify this hypothesis, (15)N nitrate injections were performed into microcosms containing different H(2)S concentrations. The ammonium (15)N enrichment was measured using an elemental analyser coupled to an isotope ratio mass spectrometer. In the two microcosms containing the highest H(2)S concentrations, the ammonium was (15)N enriched and at the end of the experiment all the added nitrate was converted into ammonium. For the two microcosms containing the lowest H(2)S concentrations, no (15)N enrichment of ammonium was observed. This isotopic approach has allowed us to demonstrate that, in the presence of significant concentrations of H(2)S, denitrification is replaced by DNRA.
Rapid Communications in Mass Spectrometry 07/2008; 22(11):1746-50. · 2.79 Impact Factor
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ABSTRACT: The biodiversity of microbial mats inhabiting the oil-contaminated lagoon Etang de Berre was determined by molecular approaches. The fingerprint of denaturing gradient gel electrophoresis (DGGE) and automatic ribosomal intergenic spacer analysis (ARISA) of mats exposed to different pollution levels showed specific microbial communities for each site but similar diversity richness. Species composition of the mats were compared by constructing 16S rRNA libraries. Amplified rDNA restriction analysis (ARDRA) of clone libraries confirmed their similar level of diversity richness. Phylogenetic analysis of the 16S rRNA sequences showed that the classes gamma and alpha of Proteobacteria were abundantly present in both sites whereas phylotypes related to the delta-Proteobacteria and to the uncultured WS3 group were mainly found in the site with the highest pollution. Identification of the species involved in oil degradation by combining culture-based approaches and DGGE, showed that enrichment cultures were constituted by members of the Rhodobacterales and species related to Rhodococcus, Sphingomonas, Xanthomonas and Microbacterium, all of them known for their ability to degrade hydrocarbons. Our findings suggest that oil pollution has not affected the biodiversity richness of the mats. However, the populations involved in hydrocarbon degradation represent a minor fraction of the mat communities in the Etang de Berre.
FEMS Microbiology Ecology 01/2007; 58(3):550-62. · 3.41 Impact Factor
