Cinétiques comparées des dégradations dans le sol du 2,4-D et du 2,4-dichlorophénol seuls ou en mélange. Conséquences sur le comportement des biomasses microbiennes dégradantes correspondantes

International audienc

Genetic rearrangement of the atzAB atrazine-degrading gene cassette from pADP1::Tn5 to the chromosome of Variovorax sp. MD1 and MD2

International audienceWe report the characterization of the rearrangement phenomena responsible for the movement of the atrazine-degrading atzA and B genes from pADP1::Tn5 to the chromosome of Variovorax sp. MD1 and MD2. Long PCRs and Southern blot analyses revealed that the two genes forming a gene cassette moved in a unique rearrangement event. It also revealed that the boundaries of the plasmid sequence inserted in the chromosome correspond to IS1071or to sequences close to IS1071. It suggests that this genetic rearrangement could result from the transposition of the composite transposon delimited by IS1071 insertion sequences and containing atzA and atzB genes. In addition, for MD1 and MD2 strains the sequencing of the remaining sequence on pADP1::Tn5 indicated that the deletion of the atzA and B genes from the plasmid might be the result of a recombination event that occurred between the IS1071 insertion sequences surrounding the atzAB gene cassette

Mécanismes d'évolution de pseudomonas sp. adp sous pression de sélection exercée par l'atrazine

L’atrazine est un pesticide qui est largement utilisé dans le monde depuis une quarantaine d’années. Son application répétée aaboutit non seulement à la contamination des eaux mais également à l’apparition de bactéries telluriques capables d’utiliserce xénobiotique comme source d’azote pour leur croissance. La caractérisation des gènes atz responsables de la dégradationde cette molécule a révélé qu’ils étaient largement dispersés et très conservés au sein du monde bactérien traduisant ainsid’une évolution et d’une dispersion récente de ces gènes, probablement concomitantes avec l’application d’atrazine dansl’environnemen

Diversity of tfdC genes: distribution and polymorphism among 2,4 dichlorophenoxyacetic acid degrading soil bacteria

International audienc

A simplified procedure for terminal restriction fragment length polymorphism analysis of the soil bacterial community to study the effects of pesticides on the soil microflora using 4,6-dinitroorthocresol as a test case

International audienceWe have studied the structural effects of application to the soil of a potentially detrimental herbicide, 4,6-dinitroorthocresol (DNOC) by analysing amplified ribosomal DNA restriction analysis (ARDRA) and terminal restriction fragment length polymorphism (T-RFLP) signatures of 16S rDNA fragments of culturable bacterial communities isolated from diluted soil suspensions. This approach has the potential to reveal changes induced by stressing the soil microflora with DNOC. This paper shows that, whereas only few changes of the ARDRA and T-RFLP profiles result from ageing of the soil, treatment of the soil with DNOC induces major modifications of these profiles. Therefore, for the practical purpose of pesticide registration, ARDRA and T-RFLP analysis performed on the dominant culturable fraction of the soil bacteria, implemented using conventional gel electrophoresis, offers the means of a routine, simple and meaningful test for detecting some of the changes affecting the structure of the soil microflora in response to pesticide application

Principaux processus impliqués dans l'atténuation naturelle des pesticides par les sols

Prod 2018-253e EA BIOmE INRANational audienc

Importance of genetic plasticity for microbial adaptation to pesticide biodegradation: in vitro evolution of Pseudomonas sp. ADP under atrazine or cyanuric acid selection pressure as case studies

International audienc

Evidence for filtering capabilities of grass buffer strips: key parameters favoring natural attenuation of pesticides in vineyard area

Communication orale, résuméVineyard is among the crops the most heavily treated with pesticides. In the context of the new EU policy for the protection of water resources, vineyard area will account as one of the major contributor to water contamination. Grass buffer strips have recently been developed as a solution for reducing pesticide transfer by surface runoff from vineyard parcels to adjacent streams. Although pesticide interception by grass strips has generally been proven effective, little is known about the fate of intercepted pesticides. In order to tackle this question we worked since several years at the scale of a small watershed located in the Beaujolais vineyard (France). The ability of the soil microflora to degrade diuron, an herbicide belonging to phenyl-urea family, was addressed by radiorespirometric analyses showing that the grass buffer strip could develop efficient degrading ability if regularly exposed to the contaminant1. Interestingly, we revealed the presence of bacterial populations able to rapidly mineralize this herbicide in the grass buffer strips. We also showed that their genetic potential (puhA and puhB genes) could be transferred by erosion to the sediment of the river adjacent to the grass buffer strip2. With the aim to promote natural attenuation of pesticides in the grass buffer strip, bioaugmentation experiments with diuron-degrading bacterial populations are ongoing. All these data seem to indicate that the development of a second generation of engineered grass buffer strip acting as an ‘in field bioreactor’ favoring pesticide biodegradation could represent an interesting tool to protect water resources in the vineyard area

Genetic plasticity of atrazine-degrader: evidence for the deletion of atzABC genes in pseudomonas sp. adp in response to cyanuric acid selection pressure

International audienceSeveral bacterial strains are known to metabolize s-triazines herbicides among which atrazine reported worldwidel to contaminate soil and water resources. The complete mineralization of atrazine to carbon dioxide and ammonium is catalyzed by 6 hydrolytic enzymes encoded by atzABCDEF genes located on the plasmid pADP1 in Pseudomonas ADP. The atzABC genes code for the upper pathway transforming atrazine to cyanuric acid, while the atzDEF genes code for the lower pathway transforming cyanuric acid to simple compounds. In order to study the genetic plasticity of the atrazine catabolic pathway, we performed an in vitro evolution study consisting in applying a continuous selection pressure with cyanuric acid as sole nitrogen source on Pseudomonas sp. After in vitro evolution the cyanuric acid degradation potential using HPLC analysis, of the native and of the newly-evolved Pseudomonas sp. population was assessed. Characterization of genetic potential revealed that the atzABC sequences were deleted in the newly-evolved population, probably by homologous recombination mediated by IS sequences. As a consequence, this in vitro evolution experiment suggests that the selection pressure exerted by the cyanuric acid led to the selection of a population showing a better fitness towards this metabolite, due to the loss of a genetic overload

In vitro evolution of an atrazine-degrading population under cyanuric acid selection pressure: Evidence for the selective loss of a 47 kb region on the plasmid ADP1 containing the atzA, B and C genes

International audienceThe adaptation of microorganisms to pesticide biodegradation relies on the recruitment of catabolic genes by horizontal gene transfer and homologous recombination mediated by insertion sequences (IS). This environment-friendly function is maintained in the degrading population but it has a cost which could diminish its fitness. The loss of genes in the course of evolution being a major mechanism of ecological specialization, we mimicked evolution in vitro by sub-culturing the atrazine-degrading Pseudomonas sp. ADP in a liquid medium containing cyanuric acid as the sole source of nitrogen. After 120 generations, a new population evolved, which replaced the original one. This new population grew faster on cyanuric acid but showed a similar cyanuric acid degrading ability. Plasmid profiles and Southern blot analyses revealed the deletion of a 47 kb region from pADP1 containing the atzABC genes coding for the enzymes that turn atrazine into cyanuric acid. Long PCR and sequencing analyses revealed that this deletion resulted from a homologous recombination between two direct repeats of a 110-bp, identical to ISPps1 of Pseudomonas huttiensis, flanking the deleted 47 kb region. The loss of a region containing three functional genes constitutively expressed thereby constituting a genetic burden under cyanuric acid selection pressure was responsible for the gain in fitness of the new population. It highlights the IS-mediated plasticity of the pesticide-degrading potential and shows that IS not only favours the expansion of the degrading genetic potential thanks to dispersion and duplication events but also contribute to its reduction thanks to deletion events