Actinomycins inhibit the production of the siderophore pyoverdines in the plant pathogen SPC9018.

Pyoverdines, a group of peptide siderophores produced by species, function not only in iron acquisition, but also in their virulence in hosts. Thus, chemical inhibition of pyoverdine production may be an effective strategy to control virulence. In the plant pathogen SPC9018 (SPC9018), pyoverdine production is required for virulence on eggplant. We screened microbial culture extracts in a pyoverdine-production inhibition assay of SPC9018 and found sp. RM-32 as a candidate-producer. We isolated two active compounds from RM-32 cultures, and elucidated their structures to be actinomycins X and D. Actinomycins X and D inhibited pyoverdine production by SPC9018 with IC values of 17.6 and 29.6 μM, respectively. Furthermore, pyoverdine production in other bacteria, such as the mushroom pathogen , was inhibited by the actinomycins. Therefore, these actinomycins may be useful as chemical tools to examine pyoverdine functions and as seed compounds for anti- virulence agents.