Impact of Leptospermone, a Natural β-Triketone Herbicide, on the Fungal Composition and Diversity of Two Arable Soils

Impact of leptospermone, a β-triketone bioherbicide, was investigated on the fungal community which supports important soil ecological functions such as decomposition of organic matter and nutrients recycling. This study was done in a microcosm experiment using two French soils, Perpignan (P) and Saint-Jean-de-Fos (SJF), differing in their physicochemical properties and history treatment with synthetic β-triketones. Soil microcosms were treated with leptospermone at recommended dose and incubated under controlled conditions for 45 days. Untreated microcosms were used as control. Illumina MiSeq sequencing of the internal transcribed spacer region of the fungal rRNA revealed significant changes in fungal community structure and diversity in both soils. Xylariales, Hypocreales, Pleosporales and Capnodiales (Ascomycota phyla) fungi and those belonging to Sebacinales, Cantharellales, Agaricales, Polyporales, Filobasidiales and Tremellales orders (Basidiomycota phyla) were well represented in treated soil microcosms compared to control. Nevertheless, while for the treated SJF a complete recovery of the fungal community was observed at the end of the experiment, this was not the case for the P treated soil, although no more bioherbicide remained. Indeed, the relative abundance of most of the saprophytic fungi were lower in treated soil compared to control microcosms whereas fungi from parasitic fungi included in Spizellomycetales and Pezizales orders increased. To the best of our knowledge, this is the only study assessing the effect of the bioherbicide leptospermone on the composition and diversity of the fungal community in soil. This study showed that leptospermone has an impact on α- and β-diversity of the fungal community. It underlines the possible interest of microbial endpoints for environmental risk assessment of biopesticide

Ecotoxicological Impact of the Bioherbicide Leptospermone on the Microbial Community of Two Arable Soils

EA BIOmEInternational audienceThe ecotoxicological impact of leptospermone, a β-triketone bioherbicide, on the bacterial community of two arable soils was investigated. Soil microcosms were exposed to 0× (control), 1× or 10× recommended dose of leptospermone. The β-triketone was moderately adsorbed to both soils (i.e.,: K fa ∼ 1.2 and K −1 oc ∼ 140 mL g). Its dissipation was lower in sterilized than in unsterilized soils suggesting that it was mainly influenced by biotic factors. Within 45 days, leptospermone disappeared almost entirely from one of the two soils (i.e., DT 50 < 10 days), while 25% remained in the other. The composition of the microbial community assessed by qPCR targeting 11 microbial groups was found to be significantly modified in soil microcosms exposed to leptospermone. Pyrosequencing of 16S rRNA gene amplicons showed a shift in the bacterial community structure and a significant impact of leptospermone on the diversity of the soil bacterial community. Changes in the composition, and in the α-and β-diversity of microbial community were transient in the soil able to fully dissipate the leptospermone, but were persistent in the soil where β-triketone remained. To conclude the bacterial community of the two soils was sensitive to leptospermone and its resilience was observed only when leptospermone was fully dissipated

Isolation and characterization of Bradyrhizobium sp. SR1 degrading two β-triketone herbicides

In this study, a bacterial strain able to use sulcotrione,a β-triketone herbicide, as sole source of carbon and energy was isolated from soil samples previously treated with this herbicide. Phylogenetic study based on16S rRNA gene sequence showed that the isolate has 100 % of similarity with several Bradyrhizobium and was accordingly designated as Bradyrhizobium sp. SR1. Plasmid profiling revealed the presence of a large plasmid (>50 kb) in SR1 not cured under nonselective conditions. Its transfer to Escherichia coli by electroporation failed to induce β-triketone degrading capacity,suggesting that degrading genes possibly located on this plasmid cannot be expressed in E. coli or that they are not plasmid borne. The evaluation of the SR1 ability to degrade various synthetic (mesotrione and tembotrione) and natural (leptospermone) triketones showed that this strain was also able to degrademesotrione. Although SR1 was able to entirely dissipate both herbicides, degradation rate of sulcotrione was ten times higher than that of mesotrione, showing a greater affinity of degrading-enzyme system to sulcotrione. Degradation pathway of sulcotrione involved the formation of 2-chloro-4-mesylbenzoic acid (CMBA), previously identified in sulcotrione degradation, and of a new metabolite identified as hydroxy-sulcotrione.Mesotrione degradation pathway leads to the accumulation of-methylsulfonyl-2-nitrobenzoic acid(MNBA) and 2-amino-4 methylsulfonylbenzoic acid(AMBA), two well-known metabolites of this herbicide. Along with the dissipation of β-triketones, one could observe the decrease in 4-hydroxyphenylpyruvate dioxygenase(HPPD) inhibition, indicating that toxicity was due to parent molecules, and not to the formed metabolites. This is the first report of the isolation of bacterial strain able to transform two β-triketones

Monoclonal Antibody-Based Immunosensor for the Electrochemical Detection of Chlortoluron Herbicide in Groundwaters

Chlortoluron (3-(3-chloro-p-tolyl)-1,1-dimethyl urea) is an herbicide widely used in substitution to isoproturon to control grass weed in wheat and barley crops. Chlortoluron has been detected in groundwaters for more than 20 years; and dramatic increases in concentrations are observed after intense rain outbreaks. In this context; we developed an immunosensor for the determination of chlortoluron based on competitive binding of specific monoclonal antibodies on chlortoluron and immobilized biotinylated chlortoluron; followed by electrochemical detection on screen-printed carbon electrodes. The optimized immunosensor exhibited a logarithmic response in the range 0.01&ndash;10 &micro;g&middot;L&minus;1; with a calculated detection limit (LOD) of 22.4 ng&middot;L&minus;1; which is below the maximum levels allowed by the legislation (0.1 &micro;g&middot;L&minus;1). The immunosensor was used for the determination of chlortoluron in natural groundwaters, showing the absence of matrix effects

Mécanismes génétiques et biochimiques impliqués dans la réponse au stress acides phénols chez Bacillus subtilis

Ce travail est une contribution à la caractérisation des mécanismes génétiques et biochimiques impliqués dans la PASR, la réponse au stress acide phénol chez les deux bactéries Gram+ Bacillus subtilis et lactobacillus plantarum. Il a porté sur l identification et la caractérisation du gène padR, le régulateur transcriptionel négatif du système et de la protéine correspondante. Il a mis en oeuvre une batterie de techniques de biologie moléculaire et cellulaire comme la mutagenèse aléatoire par transposition, la délétion de gènes, la complémentation de gènes. La caractérisation fonctionnelle qualitative et quantitative des locus ADN impliqués dans la régulation de l expression du gène padC, élément clé de la PASR, a été réalisée par de la RT-PCR qantitative, de la mutagenèse dirigée sur le promoteur régulé de ce gène padC, et aléatoire par PCR erronée sur le gène padR. Ces techniques couplées à des expressions hétérologues chez Escherichia coli ont permis en association avec des travaux de retard sur gel (EMSA) et empreinte DNAseI (Foot printing) entre protéine régulatrice et les promoteurs régulés d intérêt, d élucider une bonne partie des mécanismes.The aim of this work was to characterize the genetical and biochemical mechanisms involved in the PASR, the phenolic acid stress response induced by phenolic acids in the two Gram(+) bacteria Bacillus subtilis and Lactobacillus plantarum. It also focused on identifying and characterizing PadR, the negative transcriptional regulator involved in this response. Several strategies and techniques of molecular and cellular biology, including random transposon mutagenesis and gene deletion/complementation, were performed to elucidate the mechanisms. Qualitative and quantitative characterizations of the DNA locus involved in the regulation the padC gene expression, a key of the PASR, were achieved by quantification of qRT-PCR, by site-directed mutagenesis of the PadR regulated padC gene promoter to identify the operating sequence, and by error-prone PCR mutagenesis on the padR gene to identify essential amino acid residues. This work coupled with heterologous expressions of the PASR genes in Escherichia coli and in-vitro binding assay (EMSA) and DNAseI foot printing allowed us to elucidate the main component of the PASR.DIJON-BU Sciences Economie (212312102) / SudocSudocFranceF