AAC Accepts, published online ahead of print on 2 November 2009

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Antimicrob. Agents Chemother. doi:10.1128/AAC.00744-09
Copyright (c) 2009, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Isolation and Characterization of two Members of the Siderophore-microcin Family, Microcins M and H47

Gaëlle Vassiliadis, Delphine Destoumieux-Garzón, Carine Lombard, Sylvie Rebuffat, and Jean Peduzzi^*

Molécules de Communication et Adaptation des Micro-organismes, FRE 3206 CNRS, Muséum National d'Histoire Naturelle, CP 54, 57 rue Cuvier, 75005 Paris, France

^* To whom correspondence should be addressed. Email: peduzzi{at}mnhn.fr.

In this paper we provide the first biochemical evidence of the existence of a family of structure-related antimicrobial peptides in Enterobacteriaceae, the siderophore-microcins. We isolated and characterized here two novel siderophore-microcins, MccM and MccH47, previously characterized through genetic studies. MccM and MccH47 were expressed from several Escherichia coli strains containing the microcin gene clusters. Their spectrum of bactericidal activities was found to be restricted to some species of Enterobacteriaceae. MccM and MccH47 were unable to inhibit the growth of strains carrying mutations in the fepA, cir and fiu genes, which showed the requirement of the iron-catecholate receptors for their recognition. MccM and MccH47 peptide moieties contained 77 and 60 residues, respectively deriving from the microcin precursors McmA and MchB, respectively. In addition, both peptides carried a C-terminal posttranslational modification containing a salmochelin-like siderophore moiety also found in MccE492 (Thomas et al., J. Biol. Chem., 2004, 279, 28233-28242). Interestingly, when isolated from E. coli Nissle 1917, which lacks the two genes necessary for the modification biosynthesis, MccM was devoid of posttranslational modification. Those two genes could be complemented by their homologues from MccH47 gene cluster, thereby showing their functional interchangeability between at least two members of the siderophore-microcin family. Finally, from the sequence analysis of the MccE492 gene cluster, we hypothesized the existence of an additional member of the siderophore-microcin family. Therefore, we propose that the siderophore-microcin family contains five representatives.