Solid-state NMR determination of glyphosate metabolism in a Pseudomonas sp.

The metabolism of the broad-spectrum herbicide, glyphosate (N-phosphonomethylglycine) in a soil Pseudomonas sp. PG2982 has been determined by cross-polarization magic-angle spinning 15N and 13C NMR of intact lyophilized cells. Using samples grown on 13C- and 15N-labeled glyphosate, we find that PG2982 does not metabolize glyphosate to aminomethylphosphonate as has been reported for mixed cultures of soil microbes. Rather, the phosphonomethyl carbon-nitrogen bond in glyphosate is cleaved, releasing glycine. Solid-state NMR analysis reveals that 20% of this glycine is used in the synthesis of purines, 35% is incorporated into protein as glycyl residues, with an additional 35% incorporated as seryl residues. The phosphonomethyl carbon of glyphosate is ultimately incorporated into a number of sites, including the C-2 and C-8 positions of the purine rings of nucleic acids, methyl groups of methionine and thymidine, and the methylene group of serine. The pattern of phosphonomethyl carbon incorporation indicates the involvement of tetrahydrofolate, a coenzyme which facilitates single-carbon transfers. This is the first complete determination of the metabolism of glyphosate in a pure culture, and the first bacterial metabolic study using both single and double cross-polarization solid-state NMR.