Formation of 2,4-D bound residues in soils: New insights into microbial metabolism
Résumé
The microbial contribution to the formation of bound residues in soils is studied by characterizing the metabolic
activity of three microorganisms (Trametes versicolor, Fusarium solani and Ralstonia eutropha) on 14C-2,4-
dichlorophenoxyacetic acid (2,4-D) during incubation in synthetic liquidmedia and soil. A fractionation protocol
was applied to quantify the 14C-2,4-D thatwas incorporated into the biomass among biomolecular-like fractions.
Successive fractionation of microbial biomass was implemented to break up and quantify the methanol/dichloromethane
fraction (corresponding to the 14C-lipid-like fraction), the trichloroacetic acid fraction (or hydrolysed
14C-polysaccharide-like fraction) and the acid hydrolysable fraction (or the hydrolysed 14C-protein-like fraction).
Relevant differences in the 2,4-D degradation and biomass radioactivity distribution among the three microorganisms
were found. The 14C-protein-like fraction was the most consistent biomass fraction for reflecting the
pesticide use capacity of the microorganisms under liquid and soil conditions. 2,4-D and its metabolite 4-
chlorophenol were detected in methanol/dichloromethane and trichloroacetic acid fractions of the biomass of
microorganisms exhibiting a low capacity to mineralize 2,4-D, thus proving that the microbial participation in
the formation of bound residues while conserving the initial pesticide structure under natural soil conditions
may be intimately associatedwith the lipid- and polysaccharide-like constituents. The fractionation protocol differentiates
between 14C that is incorporated into biomass as a biomolecular constituent and the pesticide or its
metabolites that accumulate in the biomass and thus correspond to the stricto sensu definition of bound residues.
Domaines
Sciences du Vivant [q-bio]
Origine : Fichiers produits par l'(les) auteur(s)