The macrocyclic hydroxamate siderophore avaroferrin of Shewanella algae inhibits ferric iron dependent swarming motility of Vibrio alginolyticus. Investigating the biosynthesis of avaroferrin and related siderophores demonstrates the importance of the substrate pool for product formation and reveals an unprecedented flexibility in the substrate range of the responsible synthetases. Exploiting the promiscuity of these enzymes allowed to generate a broad spectrum of 15 different ring-size engineered siderophores some of which also inhibit Vibrio’s swarming behavior.