Iron(III) complexation by Vanchrobactin, a siderophore of the bacterial fish pathogen Vibrio anguillarum.

The bacterial fish pathogen Vibrio anguillarum serotype O2 strain RV22 produces the mono catecholate siderophore Vanchrobactin (Vb) under conditions of iron deficiency. Vb contains two potential bidentate coordination sites: catecholate and salicylate groups. The iron(III) coordination properties of Vb is investigated in aqueous solutions using spectrophotometric and potentiometric methods. The stepwise equilibrium constants (log K) for successive addition of Vb dianion to a ferric ion are 19.9; 13.3, and 9.5, respectively, for an overall association constant of 42.7. Based on the previous results, we estimated the equilibrium concentration of free iron(III) under physiological conditions for pH 7.4 solution containing 10(-6) M total iron and 10(-5) M total Vb as pFe = 20 (=-log[Fe(3+)]). The Vb model compounds catechol (Cat) and 2,4-dihydroxy-N-(2-hydroxyethyl)benzamide (Dhb) have also been examined, and the obtained results show that the interaction of the whole system of Vb that contains the ferric-chelating groups of both Dhb and Cat, is synergically greater than the separate parts; i.e. Vb is the best chelating agent either in acid or basic media. In summary, bacteria employing Vb-mediated iron transport thus are able to compete effectively for iron with other microorganisms within which they live.

Structural characterization of the lipopolysaccharide O-antigen from atypical isolate of Vibrio anguillarum strain 1282.

Vibrio anguillarum is a Gram-negative bacterium associated with vibriosis in Atlantic cod (Gadus morhua L.). Although farmed cod in Norway is routinely vaccinated against the infection, outbreaks of V. anguillarum-associated vibriosis still occur. Here, we describe the structural characterization of the LPS O-chain polysaccharide (O-PS) from atypical isolates of V. anguillarum strain 1282 and show that it is distinct from that previously established for V. anguillarum serotype O2. The structure of the purified O-PS was shown by 1D/2D NMR ((1)H, (13)C) spectroscopy and CE-MS studies to be a high-molecular mass linear polymer of tetrasaccharide repeating units, composed of 2-acetamido-3-(N-formyl-L-alanyl)amido-2,3-dideoxy-D-glucuronamide [GlcNAc3N(Fo-L-Ala)AN], 2-acetamido-3-acetamidino-2,3-dideoxy-D-mannuronic acid (ManNAc3NAmA), 3-acetamido-3-dideoxy-D-quinovose (Qui3NAc), and 2,4-diacetamido-2,4-dideoxy-D-fucose (FucNAc4NAc). [carbohydrate structure: see text]. NMR analysis of the partial hydrolysis-derived oligosaccharides confirmed the presence of an O-acetyl group at position O-4 of GlcNAc3N(Fo-L-Ala)AN and established that the above-mentioned structure represents the biological repeating unit of the O-PS. In addition, it was demonstrated that some of 2,3-diamino-2,3-dideoxy-glucuronamide in the O-PS was present in the form of 2,3-diamino-2,3-dideoxy-glucose.

cDNA cloning and gene expression pattern following bacterial challenge of peroxinectin in Chinese shrimp Fenneropenaeus chinensis.

Peroxinectin, a cell-adhesive hemoperoxidase that binds superoxide dismutase and mediates blood cells adhesion and migration in invertebrate, is believed to play an important role in cellular immune reaction. In this study, we reported a new peroxinectin gene homologue from Chinese shrimp Fenneropenaeus chinensis. Based on expressed sequence tags (ESTs) of haemocyte cDNA library, we cloned a 2,611 bps full-length cDNA of peroxinectin gene homologue encoded 801 amino acids. Motif scanning of the predicted polypeptide revealed a peroxidase domain and an integrin binding motif (Lys-Gly-Asp, KGD). Peroxinectin gene expressed constitutively in haemocyte as determined by quantitative real-time RT-PCR, the expression level varied following bacterial challenge. These findings suggested that peroxinectin expression is susceptible to exterior stimulus and maintains at a high expression level during bacterial infection.