The majority of bacteria need iron to grow. However, in an aerobic, pH neutral environment, the low solubility of Fe(OH)3 (Ksp=10 -39) limits the concentration of bioavailable iron to levels far below that which is required for cellular function. Pathogenic and marine bacteria face additional challenges in obtaining sufficient levels of iron because both live in very low iron environments. A shared iron acquisition strategy of marine and pathogenic bacteria is to produce and secrete siderophores into their surroundings. Siderophores are low molecular weight, organic compounds with high affinity for iron(III).

This work is focused on the investigations into siderophore production of two marine microbes, the bioluminescent Vibrio harveyi ATCC BAA-1116 and an oil-degrading Pseudoalteromonas sp..

Through genome mining, a nonribosomal peptide synthetase (NRPS) gene cluster resembling the enterobactin biosynthetic cluster is identified in the bioluminescent quorum-sensing model bacterium, V. harveyi. A predicted fatty acid CoA ligase (FACL) in the vicinity of the enterobactin biosynthetic cluster suggests that V. harveyi may produce amphiphilic enterobactin-like siderophores. Extraction of the bacterial cell pellet of V. harveyi leads to the isolation and structure determination of a suite of eight amphi-enterobactin siderophores comprised of three 2,3-dihydroxybenzoyl-L-serine residues and one acyl-L-serine arranged in a cyclic tetraseryl lactone scaffold. Gene knock-out studies confirm the involvement of the FACL and NRPS gene is the biosynthesis of the amphi-enterobactin siderophores. Biochemical characterization of the recombinant NRPS protein guides the postulation of a model for the biosynthesis of the amphi-enterobactin siderophores.

A Pseudoalteromonas sp. was isolated from the Gulf of Mexico after the Deepwater Horizon oil spill. The bacterium is determined to have hydrocarbon degrading capabilities, measured by its' growth in a medium supplemented with crude oil as the only carbon source. When grown in an iron-limited medium, three peptidic siderophores are isolated from the culture supernatant, composed of serine, asparagine, two formylated/hydroxylated ornithines, dihydroxy benzoic acid and a very unusual nonproteinogenic amino acid, 4,8-diamino-3-hydroxyoctanoic acid. The iron-binding properties of the siderophores are investigated through spectrophotometric titration. Cosmid library construction and screening leads to the identification of three cosmids potentially harboring the biosynthetic gene cluster.