Structure and activity of persicomycins, toxins produced by a Pseudomonas syringae pv. persicae/Prunus persica isolate

A toxigenic property has been demonstrated in a Pseudomonas syringae pv. persicae/Prunus persica isolate. Several substances, which are named persicomycins, have been purified in variable quantities from cultures. The structures of four of them were established by NMR and chemical ionization mass spectrometry. These compounds are 3-(3'-hydroxy)hydroxy fatty acids and thus represent a new family among the phytobacterial toxins. Other minor substances have also been isolated and have been shown to belong to the same family on the basis of their 1H-NMR spectra. All of them cause necrosis of peach tree tissues, a symptom similar to the one obtained after bacterial infection and antibiosis of microorganisms such as Bacillus thuringiensis. These results provide evidence that necrosis-inducing toxins are not restricted to the pathovar syringae. Furthermore, similar substances were purified from necrosed tissues of inoculated and diseased peach trees. 3-(3'-Hydroxydecanoyloxy)hexadecenoic acid was isolated from both such tissues and from cultures, which strongly suggests a similar toxigenesis in vivo and in vitro. The involvement of persicomycins in the die-back disease of peach trees is now clearly established, which demonstrates that the toxigenic property of the bacterium participates in the disease. The phytotoxicity of the persicomycins is discussed in comparison with the lipodepsipeptide necrotic toxins of the syringae pathovar.