Abstract
Dereplication and genome mining in Streptomyces aureus LU18118 combined with heterologous expression of selected biosynthetic gene clusters (BGCs) led to the discovery of various threonine-16:0dioic acids named lipothrenins. Lipothrenins consist of the core elements l-Thr, d-allo-Thr, or Dhb, which are linked to hexadecanedioic acid by an amide bond. The main compound lipothrenin A (1) carries the N-hydroxylated d-allo form of threonine and expresses a siderophore activity. The lipothrenin BGC was analyzed by a series of deletion experiments. As a result, a variety of interesting genes involved in the recruitment and selective activation of linear 16:0dioic acids, amide bond formation, and the epimerization of l-Thr were revealed. Furthermore, a diiron N-oxygenase was identified that may be directly involved in the monooxygenation of the amide bond. This is divergent from the usual hydroxamate formation mechanism in siderophores, which involves hydroxylation of the free amine prior to amide bond formation. Siderophore activity was observed for all N-hydroxylated lipothrenins by application of the CAS assay method.