Marion Devers

Fitness drift of an atrazine-degrading population under atrazine selection pressure.

Pseudomonas sp. ADP harbouring the atrazine catabolic plasmid ADP1 was subcultured in liquid medium containing atrazine as sole source of nitrogen. After approximately 320 generations, a new population evolved which replaced the initial population. This newly evolved population grew faster and degraded atrazine more rapidly than the initial population. Plasmid profiles and Southern blot analyses revealed that the evolved strain, unlike the ancestral strain, presented a tandem duplication of the atzB gene encoding the second enzyme of the atrazine catabolic pathway responsible for the transformation of hydroxyatrazine to N-isopropylammelide. This duplication resulted from a homologous recombination that occurred between two direct repeats of 6.2 kb flanking the atzB gene and constituted by the insertion sequences IS1071, ISPps1 and a pdhL homologous sequence. This study highlights the IS-mediated plasticity of atrazine-degrading potential and demonstrates that insertion sequences not only help to disperse the atrazine-degrading gene but also improve the fitness of the atrazine-degrading population.

Taxonomic and functional diversity of atrazine‐degrading bacterial communities enriched from agrochemical factory soil

Aims:  To characterize atrazine‐degrading potential of bacterial communities enriched from agrochemical factory soil by analysing diversity and organization of catabolic genes.

Evidence for 2,4-D mineralisation in Mediterranean soils: impact of moisture content and temperature.

BACKGROUND The 2,4-D degradation ability of the microbiota of three arable Mediterranean soils was estimated. The impact of soil moisture and temperature on 2,4-D degradation was investigated. RESULTS The microbiota of the three soils regularly exposed to 2,4-D were able rapidly to mineralise this herbicide. The half-life of 2,4-D ranged from 8 to 30 days, and maximum mineralisation of (14)C-2,4-D ranged from 57 to 71%. Extractable (14)C-2,4-D and (14)C-bound residues accounted for less than 1 and 15% respectively of the (14)C-2,4-D initially added. The highest amounts of (14)C-2,4-D bound residues were recorded in the soil with the lowest 2,4-D-mineralising ability. Although all three soils were able to mineralise 2,4-D, multivariate analysis revealed that performance of this degrading microbial activity was dependent on clay content and magnesium oxide. Soil temperature affected the global structure of soil microbial community, but it had only a moderate effect on 2,4-D-mineralising ability. 2,4-D-mineralising ability was positively correlated with soil moisture content. Negligible 2,4-D mineralisation occurred in all three soils when incubated at 10 or 15% soil moisture content, i.e. within the range naturally occurring under the Mediterranean climate of Algeria. CONCLUSION This study shows that, although soil microbiota can adapt to rapid mineralisation of 2,4-D, this microbial activity is strongly dependent on climatic parameters. It suggests that only limited pesticide biodegradation occurs under Mediterranean climate, and that arable Mediterranean soils are therefore fragile and likely to accumulate pesticide residues.

Diuron mineralisation in a Mediterranean vineyard soil: impact of moisture content and temperature

BACKGROUND The diuron-mineralising ability of the microbiota of a Mediterranean vineyard soil exposed each year to this herbicide was measured. The impact of soil moisture and temperature on this microbial activity was assessed. RESULTS The soil microbiota was shown to mineralise diuron. This mineralising activity was positively correlated with soil moisture content, being negligible at 5% and more than 30% at 20% soil moisture content. According to a double Gaussian model applied to fit the dataset, the optimum temperature/soil moisture conditions were 27.9 degrees C/19.3% for maximum mineralisation rate and 21.9 degrees C/18.3% for maximum percentage mineralisation. The impact of temperature and soil moisture content variations on diuron mineralisation was estimated. A simulated drought period had a suppressive effect on subsequent diuron mineralisation. This drought effect was more marked when higher temperatures were used to dry (40 degrees C versus 28 degrees C) or incubate (28 degrees C versus 20 degrees C) the soil. The diuron kinetic parameters measured after drought conditions were no longer in accordance with those estimated by the Gaussian model. CONCLUSION Although soil microbiota can adapt to diuron mineralisation, its activity is strongly dependent on climatic conditions. It suggests that diuron is not rapidly degraded under Mediterranean climate, and that arable Mediterranean soils are likely to accumulate diuron residues.

Genetic potential, diversity and activity of an atrazine-degrading community enriched from a herbicide factory effluent

Aims:  To characterize an atrazine‐degrading bacterial community enriched from the wastewater of a herbicide factory.