International audience | The efficacy of a wastewater treatment lagoon (WWTL) at preventing the spread of Pseudomonas aeruginosa into natural aquatic habitats was investigated. A WWTL and its connected combined sewer and brook were exhaustively sampled. Physico-chemical analyses showed a stratification of the first pond according to pH, temperature and oxygen content. The P. aeruginosa counts partially matched this stratification with higher values among the bottom anaerobic waters of the first half of this pond. Genotyping of 494 WWTL P. aeruginosa strains was performed and led to the definition of 85 lineages. Dominant lineages were observed, with some being found all over the WWTL including the connected brook. IS5 was used as an indicator of genomic changes, and 1 to 12 elements were detected among 16 % of the strains. IS-driven lasR (genetic regulator) disruptions were detected among nine strains that were not part of the dominant lineages. These insertional mutants did not show significant elastase activities but showed better growth than the PAO1 reference strain in WWTL waters. Differences in growth patterns were related to a better survival of these mutants at an alkaline pH and a better ability at using some C-sources such as alanine. The opportunistic colonization of a WWTL by P. aeruginosa can involve several metabolic strategies which appeared lineage specific. Some clones appeared more successful than others at disseminating from a combined sewer toward the overflow of a WWTL.

The efficacy of a wastewater treatment lagoon (WWTL) at preventing the spread of Pseudomonas aeruginosa into natural aquatic habitats was investigated. A WWTL and its connected combined sewer and brook were exhaustively sampled. Physico-chemical analyses showed a stratification of the first pond according to pH, temperature and oxygen content. The P. aeruginosa counts partially matched this stratification with higher values among the bottom anaerobic waters of the first half of this pond. Genotyping of 494 WWTL P. aeruginosa strains was performed and led to the definition of 85 lineages. Dominant lineages were observed, with some being found all over the WWTL including the connected brook. IS5 was used as an indicator of genomic changes, and 1 to 12 elements were detected among 16 % of the strains. IS-driven lasR (genetic regulator) disruptions were detected among nine strains that were not part of the dominant lineages. These insertional mutants did not show significant elastase activities but showed better growth than the PAO1 reference strain in WWTL waters. Differences in growth patterns were related to a better survival of these mutants at an alkaline pH and a better ability at using some C-sources such as alanine. The opportunistic colonization of a WWTL by P. aeruginosa can involve several metabolic strategies which appeared lineage specific. Some clones appeared more successful than others at disseminating from a combined sewer toward the overflow of a WWTL.

International audience | Sediment management from stormwater infiltration basins represents a real environmental and economic issue for stakeholders due to the pollution load and important tonnages of these by-products. To reduce the sediment volumes to treat, organic and metal micropollutant-bearing phases should be identified. A combination of density fractionation procedure and microanalysis techniques was used to evaluate the distribution of polycyclic aromatic hydrocarbons (PAHs) and trace metals (Cd, Cr, Cu, Ni, Pb, and Zn) within variable density fractions for three urban stormwater basin sediments. The results confirm that PAHs are found in the lightest fractions (d < 1.9, 1.9 < d < 2.3 g cm(-3)) whereas trace metals are equally distributed within the light, intermediary, and highest fractions (d < 1.9, 1.9 < d < 2.3, 2.3 < d < 2.6, and d > 2.8 g cm(-3)) and are mostly in the 2.3 < d < 2.6 g cm(-3) fraction. The characterization of the five fractions by global analyses and microanalysis techniques (XRD and MEB-EDX) allowed us to identify pollutant-bearing phases. PAHs are bound to the organic matter (OM) and trace metals to OM, clays, carbonates and dense particles. Moreover, the microanalysis study underlines that OM is the main constituent responsible for the aggregation, particularly for microaggregation. In terms of sediment management, it was shown that density fractionation is not suitable for trace metals but could be adapted to separate PAH-enriched phases.

Sediment management from stormwater infiltration basins represents a real environmental and economic issue for stakeholders due to the pollution load and important tonnages of these by-products. To reduce the sediment volumes to treat, organic and metal micropollutant-bearing phases should be identified. A combination of density fractionation procedure and microanalysis techniques was used to evaluate the distribution of polycyclic aromatic hydrocarbons (PAHs) and trace metals (Cd, Cr, Cu, Ni, Pb, and Zn) within variable density fractions for three urban stormwater basin sediments. The results confirm that PAHs are found in the lightest fractions (d < 1.9, 1.9 < d < 2.3 g cm⁻³) whereas trace metals are equally distributed within the light, intermediary, and highest fractions (d < 1.9, 1.9 < d < 2.3, 2.3 < d < 2.6, and d > 2.8 g cm⁻³) and are mostly in the 2.3 < d < 2.6 g cm⁻³fraction. The characterization of the five fractions by global analyses and microanalysis techniques (XRD and MEB-EDX) allowed us to identify pollutant-bearing phases. PAHs are bound to the organic matter (OM) and trace metals to OM, clays, carbonates and dense particles. Moreover, the microanalysis study underlines that OM is the main constituent responsible for the aggregation, particularly for microaggregation. In terms of sediment management, it was shown that density fractionation is not suitable for trace metals but could be adapted to separate PAH-enriched phases.

cited By 16 | International audience | The management of certain plant beneficial microorganisms [biological control agents (BCAs)] seems to be a promising and environmental friendly method to control plant pathogens. However, applications are still limited because of the lack of consistency of BCAs when they are applied in the field. In the present paper, the advantages and limitations of BCAs are seen through the example of Pythium oligandrum, an oomycete that has received much attention in the last decade. The biological control exerted by P. oligandrum is the result of a complex process, which includes direct effects through the control of pathogens and/or indirect effects mediated by P. oligandrum, i.e. induction of resistance and growth promotion. P. oligandrum antagonism is a multifaceted and target fungus-dependent process. Interestingly, it does not seem to disrupt microflora biodiversity on the roots. P. oligandrum has an atypical relationship with the plant because it rapidly penetrates into the root tissues but it cannot stay alive in planta. After root colonisation, because of the elicitation by P. oligandrum of the plant-defence system, plants are protected from a range of pathogens. The management of BCAs, here P. oligandrum, is discussed with regard to its interactions with the incredibly complex agrosystems. © 2013 Springer-Verlag Berlin Heidelberg.

The management of certain plant beneficial microorganisms [biological control agents (BCAs)] seems to be a promising and environmental friendly method to control plant pathogens. However, applications are still limited because of the lack of consistency of BCAs when they are applied in the field. In the present paper, the advantages and limitations of BCAs are seen through the example of Pythium oligandrum, an oomycete that has received much attention in the last decade. The biological control exerted by P. oligandrum is the result of a complex process, which includes direct effects through the control of pathogens and/or indirect effects mediated by P. oligandrum, i.e. induction of resistance and growth promotion. P. oligandrum antagonism is a multifaceted and target fungus-dependent process. Interestingly, it does not seem to disrupt microflora biodiversity on the roots. P. oligandrum has an atypical relationship with the plant because it rapidly penetrates into the root tissues but it cannot stay alive in planta. After root colonisation, because of the elicitation by P. oligandrum of the plant-defence system, plants are protected from a range of pathogens. The management of BCAs, here P. oligandrum, is discussed with regard to its interactions with the incredibly complex agrosystems.

[Departement_IRSTEA]Eaux [TR1_IRSTEA]ARCEAU | International audience | Pesticide pollution is one of the main current threats on water quality. This paper presents the potential and functioning principles of a "Wet" forest buffer zone for reducing concentrations and loads of glyphosate, isoproturon, metazachlor, azoxystrobin, epoxiconazole, and cyproconazole. A tracer injection experiment was conducted in the field in a forest buffer zone at Bray (France). A fine time-scale sampling enabled to illustrate that interactions between pesticides and forest buffer substrates (soil and organic-rich litter layer), had a retarding effect on molecule transfer. Low concentrations were observed for all pesticides at the forest buffer outlet thus demonstrating the efficiency of "Wet" forest buffer zone for pesticide dissipation. Pesticide masses injected in the forest buffer inlet directly determined concentration peaks observed at the outlet. Rapid and partially reversible adsorption was likely the major process affecting pesticide transfer for short retention times (a few hours to a few days). Remobilization of metazachlor, isoproturon, desmethylisoproturon, and AMPA was observed when non-contaminated water flows passed through the forest buffer. Our data suggest that pesticide sorption properties alone could not explain the complex reaction mechanisms that affected pesticide transfer in the forest buffer. Nevertheless, the thick layer of organic matter litter on the top of the forest soil was a key parameter, which enhanced partially reversible sorption of pesticide, thus retarded their transfer, decreased concentration peaks, and likely increased degradation of the pesticides. Consequently, to limit pesticide pollution transported by surface water, the use of already existing forest areas as buffer zones should be equally considered as the most commonly implemented grass buffer strips.

Pesticide pollution is one of the main current threats on water quality. This paper presents the potential and functioning principles of a “Wet” forest buffer zone for reducing concentrations and loads of glyphosate, isoproturon, metazachlor, azoxystrobin, epoxiconazole, and cyproconazole. A tracer injection experiment was conducted in the field in a forest buffer zone at Bray (France). A fine time-scale sampling enabled to illustrate that interactions between pesticides and forest buffer substrates (soil and organic-rich litter layer), had a retarding effect on molecule transfer. Low concentrations were observed for all pesticides at the forest buffer outlet thus demonstrating the efficiency of “Wet” forest buffer zone for pesticide dissipation. Pesticide masses injected in the forest buffer inlet directly determined concentration peaks observed at the outlet. Rapid and partially reversible adsorption was likely the major process affecting pesticide transfer for short retention times (a few hours to a few days). Remobilization of metazachlor, isoproturon, desmethylisoproturon, and AMPA was observed when non-contaminated water flows passed through the forest buffer. Our data suggest that pesticide sorption properties alone could not explain the complex reaction mechanisms that affected pesticide transfer in the forest buffer. Nevertheless, the thick layer of organic matter litter on the top of the forest soil was a key parameter, which enhanced partially reversible sorption of pesticide, thus retarded their transfer, decreased concentration peaks, and likely increased degradation of the pesticides. Consequently, to limit pesticide pollution transported by surface water, the use of already existing forest areas as buffer zones should be equally considered as the most commonly implemented grass buffer strips.