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

Dégradation biologique de la sulcotrione dans un sol agricole (recherche d une éventuelle biodégradation accélérée et caractérisation de souches bactériennes potentiellement dégradantes)

PERPIGNAN-BU Sciences (661362101) / SudocSudocFranceF

Heterogeneous photo-oxidation in microbial inactivation: A promising technology for seawater bio-securing?

This review is aimed at the actions of radical oxygen species (ROS) produced during the photocatalysis reaction on the different biomolecules composing the microorganisms, as well as the presentation and development of the key operational parameters influencing the efficiency of the photocatalytic treatment in the context of saltwater applications. Our study focuses on the case of heterogeneous photocatalysis, one of the advanced oxidation processes (AOP). This work highlights the importance of the analytical composition of the water (pH, salt, dissolved organic matter.) on the catalyst/target interactions. Similarly, the structural composition of microorganisms (cell wall biomolecules) also plays a key role in the sensitivity to the photocatalysis process, and to a lesser extent, their metabolism also has an impact on their resistance. Another important point of our work is that it highlights the fact that to date, there is no standardization in the way results from the literature are reported, making it extremely difficult to compare data for the purpose of evaluating different processes. Finally, our work underlines that photocatalysis is particularly promising for bio-securing applications like the decontamination of seawater in aquaculture via the treatment of tanks and closed aquariums, as well as for the shipping industry via the treatment of ballast water

DIAGSOL Development of a new functional marker for B-triketone herbicides exposure in agricultural soils

International audienceThe-triketone herbicides are maize selective herbicides that have been largely applied in replacement of atrazine, banned in Europe in 2004. Their mode of action lays on the inhi- bition of the p-hydroxyphenylpyruvate dioxygenase (HPPD), a key enzyme of the carotenoid biosynthesis.In recent studies, we showed that within the soil bacterial community, many microorganisms possess a functional HPPD enzyme involved in tyrosine metabolism. These ”non-target or- ganisms” harbor the target of the-triketone herbicides and consequently may be affected in response to its exposure. From this point of view, the bacterial community harboring the hppd gene might be a relevant marker to assess the ecotoxicological impact of _-triketone herbicides on soil bacterial functional diversity.Within this context, the objective of our work is to check for the interest of hppd bacterial community as a marker of exposition and/or of impact sensitive to _-triketone herbicides. This will require the development of a molecular tool box to assess the abundance, activity and diversity of the hppd bacterial community in various arable soils exposed to _-triketone herbicides. The abundance and the activity of the hppd bacterial community will be mon- itored from the nucleic acids extracted directly from soils, and the diversity of the hppd community will be evaluated by a metagenomic study based on the high-throughput se- quencing of hppd amplicons.Our results will lead to the selection of a set of characteristic hppd sequences, allowing the development of hppd DNA chips to assess the ecotoxicological impact of _-triketone herbicides on soil microorganisms

Development of a new functional marker for β-triketone herbicides exposure in agricultural soils

National audienceThe β-triketone herbicides are maize selective herbicides that have been largely applied in replacement of atrazine, banned in Europe in 2003. Their mode of action lays on the inhibition of the p-hydroxyphenylpyruvate dioxygenase (HPPD), a key enzyme of the carotenoid biosynthesis. In recent studies, we showed that within the soil bacterial community, many microorganisms possess a functional HPPD enzyme involved in tyrosine metabolism. These “non-target organisms” harbor the target of the β-triketone herbicides and consequently may be affected in response to its exposure. Within this context, the objective of our work is to check for the interest of hppd bacterial community as a marker of exposition and/or of impact sensitive to β-triketone herbicides. This will require the development of a molecular tool box to assess the abundance, activity and diversity of the hppd bacterial community in various arable soils exposed to β-triketone herbicides. The abundance and the activity of the hppd bacterial community will be monitored from the nucleic acids extracted directly from soils, and the diversity of the hppd community will be evaluated by a metagenomic study based on the high-throughput se- quencing of hppd amplicons. Our results will lead to the selection of a set of characteristic hppd sequences, allowing the development of hppd DNA chips to assess the ecotoxicological impact of β-triketone herbicides on soil microorganisms

A new tool to assess the ecotoxicological impact of β-triketone herbicides on soil microbial communities

International audienceThe β-triketone herbicides are post-emergence maize selective herbicides that have beenintroduced on the market, in replacement of atrazine, banned in Europe in 2004. Qualified as “eco-friendly”, since they are based on natural phytotoxin properties, these herbicides target an enzymeinvolved in carotenoid biosynthesis called 4-hydroxyphenylpyruvate dioxygenase (HPPD) encoded bythe hppd gene. The inhibition of this enzyme provokes bleaching symptoms, necrosis and death ofweeds.The hppd gene is not only find in eukaryotes such as plants, animals and humans but also inprokaryotes such as fungi, yeasts and bacteria. In recent studies, we showed that, within the soil bacterialcommunity, many of them possess a functional HPPD enzyme involved in tyrosine metabolism1–3.However, although soil microorganisms are classified as "non-target organisms" according to EUregulation for authorization of pesticides, they may harbor the target of the β-triketone herbicides andconsequently might be affected in response to its exposure. From this point of view, the bacterialcommunity harboring the hppd gene might be a relevant bioindicator to assess, a priori, the possiblerisks incurred by the soil ecosystem in response to an exposition to β-triketone herbicides. Thisbioindicator could also be helpful to assess, a posteriori, the ecotoxicological impact of β-triketoneherbicides on soil bacterial diversity and abundance.Within this context, the aim of our work is to check for the interest of hppd bacterial communityas a bioindicator of exposition and/or of impact sensitive to β-triketone herbicides. This will require thedevelopment of a molecular toolbox to assess the abundance, and diversity of the hppd bacterialcommunity in various arable soils exposed to β-triketone herbicides. The abundance of the hppdbacterial community will be monitored from the nucleic acids extracted directly from soils. Moreover,the diversity of the hppd community will be evaluated thanks to high-throughput sequencing of hppdamplicons obtained from the DNA and RNA extracted from the soils. Our results will lead to theselection of a set of characteristic hppd sequences, allowing the development of hppd DNA chips toassess the ecotoxicological impact of β-triketone herbicides on soil bacterial diversity.1. Romdhane, S. et al. Evidence for photolytic and microbial degradation processes in the dissipationof leptospermone, a natural β-triketone herbicide. Environ. Sci. Pollut. Res. 1–12 (2017).doi:10.1007/s11356-017-9728-42. Romdhane, S. et al. Isolation and characterization of Bradyrhizobium sp. SR1 degrading two β-triketone herbicides. Environ. Sci. Pollut. Res. Int. 23, 4138–4148 (2016).3. Calvayrac, C. et al. Isolation and characterisation of a bacterial strain degrading the herbicidesulcotrione from an agricultural soil. Pest Manag. Sci. 68, 340–347 (2012)

Pluralité des perspectives temporelles et conditions de mobilisation dans les situations de précarité d’emploi

International audienc

Interactions between pesticides and microorganisms : The case of biodegradation of synthetic β-triketone herbicides.

International audienceAgricultural use of pesticides ensures a higher crop quality and production but it is also one of the major sources of diffuse pollution in the environment. Microbial degradation is considered as an important dissipation process limiting the accumulation of pesticides in the environment. In this context, two bacterial strains able to degrade sulcotrione, a β-triketone herbicide, were isolated from an agricultural soil previously exposed to this herbicide. The two isolates were identified using 16S rRNA gene sequencing as Pseudomonas sp.1OP and Bradyrhizobium sp.SR1. Their capacity to degrade sulcotrione was estimated and 2-Chloro-4-mesylbenzoic acid, one of its main metabolites, was clearly detected. Their ability to degrade other β-triketone herbicides was tested showing that only Bradyrhizobium sp.SR1 was able to completely degrade mesotrione and producing already known metabolites. Microbial toxicity of sulcotrione and mesotrione and their related metabolites in bacterial cultures was estimated by monitoring 4-hydroxyphenylpyruvate dioxygenase (HPPD) enzyme inhibition. Our results indicate that triketone herbicides toxicity linked to HPPD inhibition was due to parent molecules and not to the formed metabolites. Attempts were done to identify the genetic localization of sulcotrione degradation in Pseudomonas sp.1OP and Bradyrhizobium sp.SR1. Plasmid profiles of both strains revealed the presence of large plasmids (>12 kb and >50 kb, respectively). Curing experiments showed that Pseudomonas sp.1OP lost its ability to degrade sulcotrione under non-selective conditions, therefore degradation capacity may be attributed to the presence of this plasmid. On the contrary, under the same conditions, Bradyrhizobium sp.SR1 plasmid was not cured and the sulcotrione-degrading ability of the strain was maintained. Furthermore, a 14 000 Tn5 mutant library was constructed using a Tn5 mutagenesis approach conducted on Bradyrhizobium sp. SR1. Among this library, two mutants affected in their biodegradation capacity were identified. Full sequencing of SR1 and Tn5 mutants is ongoing to identify possible degrading gene candidates