Fate and ecotoxicological impact of new generation herbicides from the triketone family: An overview to assess the environmental risks.

Triketones, derived chemically from a natural phytotoxin (leptospermone), are a good example of allelochemicals as lead molecules for the development of new herbicides. Targeting a new and key enzyme involved in carotenoid biosynthesis, these latest-generation herbicides (sulcotrione, mesotrione and tembotrione) were designed to be eco-friendly and commercialized fifteen-twenty years ago. The mechanisms controlling their fate in different ecological niches as well as their toxicity and impact on different organisms or ecosystems are still under investigation. This review combines an overview of the results published in the literature on ß-triketones and more specifically, on the commercially-available herbicides and includes new results obtained in our interdisciplinary study aiming to understand all the processes involved (i) in their transfer from the soil to the connected aquatic compartments, (ii) in their transformation by photochemical and biological mechanisms but also to evaluate (iii) the impacts of the parent molecules and their transformation products on various target and non-target organisms (aquatic microorganisms, plants, soil microbial communities). Analysis of all the data on the fate and impact of these molecules, used pure, as formulation or in cocktails, give an overall guide for the assessment of their environmental risks.

In vivo 31P and 13C NMR investigations of Rhodococcus rhodochrous metabolism and behaviour during biotransformation processes.

AIMS: The strain Rhodococcus rhodochrous OBT18 was isolated from a water treatment plant used to decontaminate industrial effluents containing benzothiazole derivatives. Aims of the work are to study the central metabolism of this strain and more specifically its behaviour during biodegradation of 2-aminobenzothiazole. METHODS AND RESULTS: In vivo(13)C and (31)P NMR experiments showed that this strain contains storage compounds such as polyphosphates, glycogen and trehalose and produces biosurfactants containing trehalose as sugar unit. Trehalose can be synthesized after reversion of the glycolytic pathway. In vivo(31)P NMR experiments showed that energy metabolism markers such as the intracellular pH and the ATP concentration did not change during biotransformation processes when R. rhodochrous was exposed to potentially toxic compounds including iron complexes and (* )OH radicals. Also R. rhodochrous recovers the normal values of ATP and pH after anoxia/reoxygenation cycle very quickly. CONCLUSIONS: Rhodococcus rhodochrous carbon and energy metabolism is well adapted to different stresses and consequently to live in the environment where conditions are constantly changing. SIGNIFICANCE AND IMPACT OF THE STUDY: The results of this study can be used to understand the behaviour of this bacterium in natural environments but also in water treatment plants where iron and UV light are present.

First isolation and characterization of a bacterial strain that biotransforms the herbicide mesotrione.

AIM: The aim of this study was to find and characterize a fungal or bacterial strain capable of metabolizing mesotrione, a new selective herbicide for control of broad-leaved weeds in maize. METHODS AND RESULTS: This strain was isolated from cloud water and showed close phylogenetic relationship with strains belonging to the Bacillus genus, based on 16S rRNA gene alignment. Kinetics of mesotrione degradation were monitored by high-performance liquid chromatography and in situ(1)H nuclear magnetic resonance spectroscopy at different concentrations. Mesotrione was completely biotransformed even at 5 mmol l(-1) concentration. 2-Amino-4-methylsulfonyl benzoic acid (AMBA) was identified as one of the metabolites, but was not the major one. CONCLUSIONS: This study reports the first rapid mesotrione biotransformation by a pure bacterial strain and the formation of several metabolites including AMBA. SIGNIFICANCE AND IMPACT OF THE STUDY: This bacterium isolated from cloud water is the first pure strain capable of rapidly degrading mesotrione.