NUCLEAR-MAGNETIC-RESONANCE TIMECOURSE STUDIES OF GLYPHOSATE METABOLISM BY MICROBIAL SOIL ISOLATES

1. Triple Resonance Isotope EDited nmr spectroscopy (TRIED) has been d eveloped to detect and examine minute levels of glyphosate metabolites in microbial soil isolates. Using stable isotopic labelling (C-13 and N-15), TRIED allows the simultaneous detection of multiple metabolite s in crude matrices at submicrogram levels. An improvement over earlie r techniques where milligrams are needed, TRIED can detect 500 ng of t riply labelled compound in a crude sample (1:14000 mass ratio) in just hours. 2. TRIED is used here to compare the kinetics and metabolic pa thways of glyphosate metabolism by two strains of Ochrobactrum anthrop i, LBAA and Si. Both LBAA and S5 appear to metabolize glyphosate prima rily via the aminomethylphosphonate (AMPA) pathway, since no detectabl e levels of glycine or sarcosine are observed in the media or lysates of either microbe. The formation of N-methylAMPA is common to the meta bolism of both microorganisms, but N-acetylAMPA is observed only in LB AA. N-methylacetamide is detected predominantly in media and lysates o f S5, although some evidence also points to the formation of this meta bolite in LBAA. 3. Results are consistent with conventional radioactiv e tracer studies. TRIED nmr provides more specific structural informat ion complementary to radiolabel methods. Both nmr and radioactivity st udies show S5 glyphosate metabolism to be much slower than that of LBA A.