Biosynthetic origin of syringomycin and syringopeptin 22, toxic secondary metabolites of the phytopathogenic bacterium Pseudomonas syringae pv. syringae

The biosynthesis of syringomycin (SR) and syringo-peptin 22 (SP22), bioacti ve lipodepsipeptides of the phytopathogenic bacterium Pseudomonas syringae pv. syringae, was studied by feeding C-14-labeled precursors to chloramphen icol-containing bacterial suspensions. The preferential sites of incorporat ion were determined by comparing the specific activities of the intact radi olabeled metabolites and their single structural elements, obtained by hydr olytic degradation followed by derivatization and isolation by high perform ance liquid chromatography. The results show that, upon feeding L-[C-14(U)] -Thr, 35.0 and 31.0% of the SR radioactivity is retained in 2,3-dehydro-2-a minobutyric acid (Dhb) and 4-chlorothreonine (Thr(4-Cl)), respectively. L-[ C-14(U)]-Asp labels the same sites, though less efficiently, and is also in corporated in 2,4-diaminobutyric acid (Dab) and 3-hydroxyaspartic acid (Asp (3-OH)), Dhb is also labeled by Thr and Asp in SP22, These are the first da ta on the biosynthetic origin of the modified residues in P.d syringae lipo peptides, (C) 1999 Federation of European Biochemical Societies.