Siderophores of Marinobacter aquaeolei: petrobactin and its sulfonated derivatives

Abstract

Siderophores are low molecular weight, high-affinity iron(III) ligands, produced by bacteria to solubilize and promote iron uptake under low iron conditions. Two prominent structural features characterize the majority of the marine siderophores discovered so far: (1) a predominance of suites of amphiphilic siderophores composed of an iron(III)-binding headgroup that is appended by one or two of a series of fatty acids and (2) a prevalence of siderophores that contain alpha-hydroxycarboxylic acid moieties (e.g., beta-hydroxyaspartic acid or citric acid) which are photoreactive when coordinated to Fe(III). Variation of the fatty acid chain length affects the relative amphiphilicity within a suite of siderophores. Catecholate sulfonation is another structural variation that would affect the hydrophilicity of a siderophore. In addition to a review of the marine amphiphilic siderophores, we report the production of petrobactin disulfonate by Marinobacter aquaeolei VT8.

Fig. 1

Structures of amphiphilic marine siderophores: Marinobactins and Aquachelins (Martinez et al. 2000), Amphibactins (Martinez et al. 2003), Loihichelins (Homann et al. 2009), Ohrobactins (Martine et al. 2006), Synechobactins (Ito and Butler 2005). The circled moieties are the α-hydroxycarboxylic acids or a α-hydroxycarboxyamide that is photoreactive when coordinated to Fe(III)

Fig. 2

Examples of non amphiphilic marine peptide and citrate siderophores: Alterobactins (Reid et al. 1993), Pseudoalterobactins (Kanoh et al. 2003), Aerobactin (Haygood et al. 1993), Vibrioferrin (Amin et al. 2007)

Fig. 3

Tandem mass spectrum of petrobactin-(SO₃)₂. Inset: Structure of petrobactin-(SO₃)₂ showing the “y” and “b” fragmentation (Roepstorff and Fohlmann 1984) from the tandem mass spectrum