Vanadium bromoperoxidase from Delisea pulchra: enzyme-catalyzed formation of bromofuranone and attendant disruption of quorum sensing.

Vanadium bromoperoxidase was isolated and cloned from the marine red alga Delisea pulchra. This enzyme catalyzes the bromolactonization of 4-pentynoic acid forming 5E-bromo-methylidenetetrahydro-2-furanone, a compound which is shown herein to inhibit quorum sensing in the engineered reporter strain, Agrobacterium tumefaciens NTL4.

Siderophore production by marine-derived fungi.

Siderophore production by marine-derived fungi has not been extensively explored. Three studies have investigated the ability of marine-derived fungi to produce siderophores in response to iron limitation [(Vala et al. in Indian J Mar Sci 29:339-340, 2000; Can J Microbiol 52:603-607, 2006); Baakza et al. in J Exp Mar Biol Ecol 311:1-9, 2004]. In all, 24 of 28 marine fungal strains were found to secrete hydroxamate or carboxylate siderophores; no evidence was found for production of catecholate siderophores. These studies did not determine the structures of the iron-binding compounds. More recently, a study of the natural products secreted by a marine Penicillium bilaii revealed that this strain produced the rare catecholate siderophore pistillarin when grown under relatively high iron concentrations (Capon et al. J Nat Prod 70:1746-1752, 2007). Additionally, the production of rhizoferrin by a marine isolate of Cunninghamella elegans (ATCC36112) is reported in this manuscript. The current state of knowledge about marine fungal siderophores is reviewed in light of these promising results.

Structure and membrane affinity of new amphiphilic siderophores produced by Ochrobactrum sp. SP18.

The coastal alpha-proteobacterium Ochrobactrum sp. SP18 produces a suite of three citrate-derived, cell-associated amphiphilic siderophores, ochrobactins A-C. The ochrobactins are composed of a citric acid backbone amide-linked to two lysine residues. Each epsilon-amine of lysine is hydroxylated and acylated forming two hydroxamic acid moieties. One of the acylated appendages of each ochrobactin is (E)-2-decenoic acid. The other acylated appendages for ochrobactins A-C are (E)-2-octenoic acid, octanoic acid and (E)-2-decenoic acid, respectively. The ferric ochrobactin complexes are photoreactive in UV light, producing an oxidized ligand with loss of 46 mass units that can still coordinate Fe(III). The relative partitioning of the apo-ochrobactins, Fe(III) ochrobactins and Fe(III) photoproducts into 1,2-dimyristoyl-sn-glycero-3-phosphocholine vesicles is presented. The ochrobactins are the first example of aerobactin-based siderophores with two fatty acid appendages produced in a suite with varying acyl appendage lengths.

Structure and membrane affinity of a suite of amphiphilic siderophores produced by a marine bacterium.

Iron concentrations in the ocean are low enough to limit the growth of marine microorganisms, which raises questions about the molecular mechanisms these organisms use to acquire iron. Marine bacteria have been shown to produce siderophores to facilitate iron(III) uptake. We describe the structures of a suite of amphiphilic siderophores, named the amphibactins, which are produced by a nearshore isolate, gamma Proteobacterium, Vibrio sp. R-10. Each amphibactin has the same Tris-hydroxamate-containing peptidic headgroup composed of three ornithine residues and one serine residue but differs in the acyl appendage, which ranges from C-14 to C-18 and varies in the degree of saturation and hydroxylation. Although amphiphilic siderophores are relatively rare, cell-associated amphiphilic siderophores are even less common. We find that the amphibactins are cell-associated siderophores. As a result of the variation in the nature of the fatty acid appendage and the cellular location of the amphibactins, the membrane partitioning of these siderophores was investigated. The physiological mixture of amphibactins had a range of membrane affinities (3.8 x 10(3) to 8.3 x 10(2) M(-1)) that are larger overall than other amphiphilic siderophores, likely accounting for their cell association. This cell association is likely an important defense against siderophore diffusion in the oceanic environment. The phylogenetic affiliation of Vibrio sp. R-10 is discussed, as well as the observed predominance of amphiphilic siderophores produced by marine bacteria in contrast to those produced by terrestrial bacteria.