title: Biosynthetic analysis of the petrobactin siderophore pathway from Bacillus anthracis.
abstract: The asbABCDEF gene cluster from Bacillus anthracis is responsible for biosynthesis of petrobactin, a catecholate siderophore that functions in both iron acquisition and virulence in a murine model of anthrax. We initiated studies to determine the biosynthetic details of petrobactin assembly based on mutational analysis of the asb operon, identification of accumulated intermediates, and addition of exogenous siderophores to asb mutant strains. As a starting point, in-frame deletions of each of the genes in the asb locus (asbABCDEF) were constructed. The individual mutations resulted in complete abrogation of petrobactin biosynthesis when strains were grown on iron-depleted medium. However, in vitro analysis showed that each asb mutant grew to a very limited extent as vegetative cells in iron-depleted medium. In contrast, none of the B. anthracis asb mutant strains were able to outgrow from spores under the same culture conditions. Provision of exogenous petrobactin was able to rescue the growth defect in each asb mutant strain. Taken together, these data provide compelling evidence that AsbA performs the penultimate step in the biosynthesis of petrobactin, involving condensation of 3,4-dihydroxybenzoyl spermidine with citrate to form 3,4-dihydroxybenzoyl spermidinyl citrate. As a final step, the data reveal that AsbB catalyzes condensation of a second molecule of 3,4-dihydroxybenzoyl spermidine with 3,4-dihydroxybenzoyl spermidinyl citrate to form the mature siderophore. This work sets the stage for detailed biochemical studies with this unique acyl carrier protein-dependent, nonribosomal peptide synthetase-independent biosynthetic system.
authors.affiliation: Life Sciences Institute, Department of Medicinal Chemistry, University of Michigan, Ann Arbor, MI 48109-2216, USA.
authors.forename: Jung Yeop
authors.initials: JY
authors.lastname: Lee
authors.forename: Brian K
authors.initials: BK
authors.lastname: Janes
authors.forename: Karla D
authors.initials: KD
authors.lastname: Passalacqua
authors.forename: Brian F
authors.initials: BF
authors.lastname: Pfleger
authors.forename: Nicholas H
authors.initials: NH
authors.lastname: Bergman
authors.forename: Haichuan
authors.initials: H
authors.lastname: Liu
authors.forename: Kristina
authors.initials: K
authors.lastname: Håkansson
authors.forename: Ravindranadh V
authors.initials: RV
authors.lastname: Somu
authors.forename: Courtney C
authors.initials: CC
authors.lastname: Aldrich
authors.forename: Stephen
authors.initials: S
authors.lastname: Cendrowski
authors.forename: Philip C
authors.initials: PC
authors.lastname: Hanna
authors.forename: David H
authors.initials: DH
authors.lastname: Sherman
mesh_terms: D001408:Bacillus anthracis / Q000254:growth & development / Q000378:metabolism*; D001483:Base Sequence; D001549:Benzamides / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D005816:Genetic Complementation Test; D007501:Iron / Q000378:metabolism; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D009154:Mutation; D009876:Operon
chemical_list: D001549:Benzamides; C450699:petrobactin; D007501:Iron