Contribution of ecotoxicological tests in the evaluation of soil bioremediation efficiency

Clean-up of contaminated soils became a high priority only recently. Several techniques have been developed forthis purpose such as chemical, physical, thermic or microbiological methods. Efficiency of the remediation can be estimated using two approaches : a chemical specific approach and a toxicity-based approach. So far, the efficiency of the decontamination process was based essentially on chemical analyses which does not integrale the toxicity of all the soil contaminants and does not give a response on effects caused by the bioavailable fraction of these contaminants äs the toxicity-based approach. In the present study, bioremediation efficiency of a soil contaminated by 4-chlorobiphenyl was evaluated using chemical and biological analyses. Experiments were carried out in microcosms contaminated at a rate of 1 g/kg. Control microcosms without specific degrader were performed simultaneously. Acute toxicity to earthworms and inhibition of growth of barley roots were selected, from previous work, äs relevant ecotoxicological test

Evaluation of a bioremediation process efficiency : contribution of analytical, microbiological, molecular and ecotoxicological methods

International audienceIn order to set the parameters of the experiments, the study was first carried out in artificial soil microcosms contaminated with 4-chlorobiphenyl. A biphenyl degrader, Pseudomonas sp. B4, was introduced into the microcosm and its presence was checked by microbiological and molecular methods

The use of quantitative PCR, plant and earthworm bioassays, plating and chemical analysis to monitor 4-chlorobiphenyl biodegradation in soil microcosms

International audience4-Chlorobiphenyl biodegradation was monitored using several methods including molecular detection, microbiological and ecotoxicological techniques and analytical tools. Experiments were carried out in microcosms with artificial soil and an uncultivated sandy loam soil, contaminated at a rate of 1 g kg(-1) of 4-chlorobiphenyl. Two strains were used for bioremediation: a 4-chlorobiphenyl degrader, the bacterial strain Pseudomonas sp, strain B4 and the bacterial strain Pseudomonas sp, strain CBS3 which is able to mineralize 4-chlorobenzoate. Molecular tools were constructed for the detection and the quantification of dihydroxybiphenyl dioxygenase gene (bphC) from Pseudomonas sp. strain B4 and for the detection of the 4-chlorobenzoate coenzyme A dehalogenase gene from Pseudomonas sp. strain CBS3. Evidence was found for 4-chlorobiphenyl toxicity to barley and earthworms using standardized ecotoxicological tests. When Pseudomonas sp. strain B4 was introduced alone into microcosms, no decrease in toxicity occurred although 4-chlorobiphenyl was entirely degraded. The introduction of Pseudomonas sp. strain CBS3 into inoculated microcosms resulted in the disappearance of the 4-chlorobenzoate accumulated during the degradation of 4-chlorobiphenyl by Pseudomonas sp. strain B4, and in the disappearance of any toxic effect indicating that remediation was complete. Similar results were obtained independent of the nature of the soil used in microcosms. These results underline the need for taking biological effects into account in order to assess remediation efficiency

Isolation, characterization and diuron transformation capacities of a bacterial strain arthrobacter sp N2

International audienceA bacterial strain able to transform diuron was isolated from a soil by enrichment procedures. Strain isolation was realized by plating on minimal-agarose medium spread with this herbicide and selecting the colonies surrounded by a clear thin halo. One strain was characterized and identified as an Arthrobacter sp. It metabolized diuron and the final transformation product, 3,4-dichloroaniline, was produced in stoichiometric amounts. The transformation of diuron at different concentrations was more efficient in the presence of alternative sources of carbon and nitrogen. The bacterial activity was also evaluated in soil microcosms with a consequent disappearance of diuron and concomitant appearance of 3,4-dichloroaniline, of which the concentration decreased thereafter. Bacterial cells inoculated in the microcosms survived as viable but eventually nonculturable cells

Degradation of morpholine and thiomorpholine by an environmental Mycobacterium involves a cytochrome P450. Direct evidence of intermediates by in situ NMR

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Degradation of Morpholine by an Environmental Mycobacterium Strain Involves a Cytochrome P-450

A Mycobacterium strain (RP1) was isolated from a contaminated activated sludge collected in a wastewater treatment unit of a chemical plant. It was capable of utilizing morpholine and other heterocyclic compounds, such as pyrrolidine and piperidine, as the sole source of carbon, nitrogen, and energy. The use of in situ (1)H nuclear magnetic resonance ((1)H NMR) spectroscopy allowed the determination of two intermediates in the biodegradative pathway, 2-(2-aminoethoxy)acetate and glycolate. The inhibitory effects of metyrapone on the degradative abilities of strain RP1 indicated the involvement of a cytochrome P-450 in the biodegradation of morpholine. This observation was confirmed by spectrophotometric analysis and (1)H NMR. Reduced cell extracts from morpholine-grown cultures, but not succinate-grown cultures, gave rise to a carbon monoxide difference spectrum with a peak near 450 nm, which indicated the presence of a soluble cytochrome P-450. (1)H NMR allowed the direct analysis of the incubation medium containing metyrapone, a specific inhibitor of cytochrome P-450. The inhibition of morpholine degradation was dependent on the morpholine/metyrapone ratio. The heme-containing monooxygenase was also detected in pyrrolidine- and piperidine-grown cultures. The abilities of different compounds to support strain growth or the induction of a soluble cytochrome P-450 were assayed. The results suggest that this enzyme catalyzes the cleavage of the C—N bond of the morpholine ring