From the cultures ofPseudomonas putidaBTP 1 a siderophore could be isolated which contains the chromophore2arather than1atypical for pyoverdins. Its structure was elucidated by MS, NMR and chemical degradation. This new structural type is of great interest: The currently accepted biogenetic pathway leading to1astarts from D-Tyr and L-Dab which condense to give the ferribactin chromophore4. Subsequent ring closure via the α-nitrogen of Dab leads to1awhile the alternative ring closure via the γ-nitrogen would yield2a. It is for the first time that this isochromophore has been detected in aPseudomonassiderophore. Its discovery confirms the assumed intermediacy of ferribactins in the biogenesis of pyoverdins.