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Insight into Siderophore-Carrying Peptide Biosynthesis: Enterobactin Is a Precursor for Microcin E492 Posttranslational Modification

Gaëlle Vassiliadis, Jean Peduzzi,^* Séverine Zirah, Xavier Thomas, Sylvie Rebuffat, and Delphine Destoumieux-Garzón

Chimie et Biochimie des Substances Naturelles, CNRS-Muséum National d'Histoire Naturelle, UMR 5154, CP 54, 57 rue Cuvier, 75005 Paris, France

Received 21 February 2007/ Returned for modification 22 May 2007/ Accepted 17 July 2007

Microcin E492-producing bacteria secrete both unmodified and posttranslationally modified microcins. The modification consists of a C-glucosylated linear trimer of N-(2,3-dihydroxybenzoyl)-L-serine, a catecholate siderophore related to salmochelins and enterobactin. We show here that repression of enterobactin biosynthesis inhibits the acquisition of microcin E492 posttranslational modification, as monitored by high-performance liquid chromatography and mass spectrometry. Furthermore, exogenous enterobactin restored the production of posttranslationally modified microcin in a bacterial strain deficient in enterobactin synthesis. We thus concluded that enterobactin serves as a precursor for the synthesis of the posttranslationally modified microcin and that the unmodified microcin is an incompletely processed form of mature microcin E492. Gene disruption experiments showed that MceC and MceD, two enzymes encoded by the mceABCDEFGHIJ gene cluster, are involved in the synthesis of the microcin E492 posttranslational modification, as followed by mass spectrometry. Genes homologous to iroB and iroD, required for the conversion (linearization and C-glycosylation) of enterobactin into salmochelins, efficiently complemented mceC and mceD, respectively. Based on our results, a model is proposed for the biosynthesis of the mature siderophore-carrying peptide.

Published ahead of print on 23 July 2007.

Present address: Laboratoire d'Etude des Parasites Génétiques, CNRS-Université François Rabelais, FRE 2535, Parc de Grandmont, Avenue Monge, 37200 Tours, France.

Present address: ECOLAG, CNRS-Ifremer-Université Montpellier II, UMR 5119, Place Eugène Bataillon, CC 80, 34095 Montpellier Cedex 5, France.