Ruckerbactin Produced by Yersinia ruckeri YRB Is a Diastereomer of the Siderophore Trivanchrobactin Produced by Vibrio campbellii DS40M4

The Gram-negative bacterium Yersinia ruckeri is the causative agent for enteric red mouth disease in salmonids. The genome of Y. ruckeri YRB contains a biosynthetic gene cluster encoding the biosynthesis of catechol siderophores that are diastereomeric with the known vanchrobactin class of siderophores, (DHB^DArg^LSer)_(1–3). Ruckerbactin (1), produced by Y. ruckeri YRB, was found to be the linear tris-l-serine ester composed of l-arginine and 2,3-dihydroxybenzoic acid, (DHB^LArg^LSer)₃. The biscatechol, (DHB^LArg^LSer)₂ (2), and monocatechol, DHB^LArg^LSer (3), compounds were also isolated and characterized. The macrolactone of ruckerbactin was not detected. The presence of ^LArg in ruckerbactin makes it the diastereomer of trivanchrobactin with ^DArg. The electronic circular dichroism spectra of Fe­(III)–ruckerbactin and Fe­(III)–trivanchrobactin reveal the opposite enantiomeric configurations at the Fe­(III) sites. Fe­(III)–ruckerbactin adopts the Δ configuration, and Fe­(III)–trivanchrobactin adopts the Λ configuration. Y. ruckeri YRB was also found to produce the antimicrobial agent holomycin (4).