6533b7dafe1ef96bd126f384

RESEARCH PRODUCT

DIAGSOL : development of a new functional marker of exposure to herbicides B-triketones in an agricultural soil

subject

description

Numerous herbicides target an enzyme found not only in weeds but also in « non-target organisms » such as microorganisms. This proof-of-concept study aims to use microbial gene encoding the targeted enzyme or the targeted enzyme itself as a marker for herbicide exposure in soils. The hppd gene and the encoded enzyme (HPPD; 4-hydroxyphenylpyruvate dioxygenase), targeted by B-triketone herbicides, are the subject of this study. In silico analyses reveal that the hppd gene is spread out in all bacterial phyla. Primers specific to this gene were designed. This primer pair is used to measure the abundance, the composition and the diversity of the hppd bacterial community in soil microcosms exposed to sulcotrione or its commercial formulation, Decano®. Similar measurements are made, over a cropping cycle, on agricultural fields treated with various herbicides, including B-triketones. No significant effect of B-triketone herbicides were observed at the bacterial community scale, strengthening their “eco-friendly” reputation. At the enzymatic scale, molecular docking studies reveal that B-triketones bind more closely to certain bacterial HPPD than others. The developed bioassay reinforces this observation: regarding the bacterial strain, ?-triketones have a variable inhibitory effect on the HPPD enzymatic activity. Tembotrione has a greater inhibitory effect on the HPPD activity of Bacillus cereus ATCC14579 and Shewanella oneidensis MR1 than sulcotrione and mesotrione. This bioassay could be used as a marker of exposure for B-triketones risk assessment studies requested by authorities in charge of pesticide regulation.