Biosynthesis of bioactive lipodepsipeptides by Pseudomonas syringae pv. syringae.

The biosynthesis of the lipodepsipeptides syringomycin and syringopeptin 22, secondary metabolites produced by the strain B301D-R of the phytopathogenic bacterium Pseudomonas syringae pv. syringae, was investigated by feeding radioactively labeled precursors to chloramphenicol-contg. bacterial suspensions. The prodn. of labeled metabolites in the presence of a protein biosynthesis inhibitor showed that a nonribosomal mechanism is operating in their synthesis. The origin of the modified amino acidic residues was studied by comparing the specific activities of the intact lipodepsipeptides, derived from the feedings of L-[14C(U)]-Thr or L-[14C(U)]-Asp, to those of the constituent amino acids, obtained by hydrolytic degrdn. of the peptides, followed by appropriate derivatizations and isolation of the single structural elements by RP-HPLC. The results show that L-threonine is the precursor of dehydrobutyrin in syringomycin and in syringopeptin 22 and of 4-chlorothreonine in syringomycin. These two residues are also labeled by aspartic acid, which is the biosynthetic precursor of threonine. Moreover, aspartic acid is also incorporated into 2,4-diaminobutyric and 3-hydroxyaspartic acid in syringomycin.