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

International audience; The 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).