Heterobactins: A new class of siderophores from Rhodococcus erythropolis IGTS8 containing both hydroxamate and catecholate donor groups

We report here on a new class of siderophores isolated from Rhodococcus ery thropolis IGTS8, the first structurally characterized from any species of R hodococcus and for which we suggest the name heterobactins. These sideropho res consist of a tripeptide of sequence (N-OH)-L-Orn-Gly-D-Orn-(delta -N-di hydroyxbenzoate). The alpha amino group of the D-Orn is derivatized either as a 2-hydroxybenzoxazolate in heterobactin A or remains free in heterobact in B. The structures were determined by a combination of amino acid analysi s, mass spectrometry and NMR methods. The two new compounds are true sidero phores in that they relieve iron limited growth in the producing strain. Th e heterobactins are also transported by other non-producing bacteria. Growt h promotion tests using various transport mutants revealed that in E. coli heterobactin A is only recognized by the catecholate receptor Cir while het erobactin B is taken up in both E. coli and A. flavescens JG9 via a hydroxa mate transport system.