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Tenacibaculum maritimum is the aetiological agent of an ulcerative disease known as tenacibaculosis, which affects a large number of marine fish species in the world and is of considerable economic significance to aquaculture producers. Problems associated with epizootics include high mortality rates, increased susceptibility to other pathogens, high labour costs of treatment and enormous expenditures on chemotherapy. In the present article we review current knowledge on this bacterial pathogen, focusing on important aspects such as the phenotypic, serologic and genetic characterization of the bacterium, its geographical distribution and the host species affected. The epizootiology of the disease, the routes of transmission and the putative reservoirs of T. maritimum are also discussed. We include a summary of molecular diagnostic procedures, the current status of prevention and control strategies, the main virulence mechanisms of the pathogen, and we attempt to highlight fruitful areas for continued research. TAXONOMYThe taxonomy of Tenacibaculum maritimum was a matter of controversy and confusion for decades, and it has only recently been clarified by Suzuki et al. (2001). Masumura & Wakabayashi (1977) isolated a gliding bacterium that had caused mass mortalities among certain cultured marine fish. These strains were characterized by Hikida et al. (1979), who announced their intention to make a separate formal proposal of the name Flexibacter marinus. Since the epithet marinus had already been used in the name Vibrio marinus, the authors changed their mind on the use of this epithet, and the eventual formal proposal was a taxon called Flexibacter maritimus (Wakabayashi et al. 1986, Holmes 1992. Reichenbach (1989) listed the pathogen as Cytophaga marina, but the priority of the name Flexibacter maritimus was later recognized (Holmes 1992). These results were confirmed by Bernardet & Grimont (1989), who also validated the name Flexibacter maritimus based on DNA-DNA hybridisation methods.However, the resolution of phenotypic characterization and 16S ribosomal RNA (rRNA) sequence analysis is insufficient to distinguish closely related organisms. Thus, Suzuki et al. (2001), based on the nucleotide sequence of the gyrB, proposed that Flexibacter maritimus should be transferred to the new genus Tenacibaculum, in which 7 members are currently included. Table 1 shows the main differential characteristics of the described species of the genus Tenacibaculum. GEOGRAPHICAL DISTRIBUTION AND HOST SPECIESThe geographical distribution of Tenacibaculum maritimum in wild and farmed fish is shown in Table 2. 256 Characteristic T. maritimum T. ovolyticum T. mesophilum T. amilotyticum T. skagerrakense T. lutimarisOrigin Diseased red sea Halibut egg, Sponge and Macroalgae, Pelagic, Tidal flat, bream fingerling, Japan Norway macroalgae, Japan Japan Denmark Korea Cells size (µm) 2-30 × 0.5 2-20 × 0.5 1.5-10 × 0.5 2-4 × 0.4 2-15 × 0.5 2-10 × 0. Percentage of NaCl in the medium Table 1. Differential phenotypic characteris...

A survey of antibiotic-producing bacteria from the microbial flora attached to seaweeds and the study of their antibiotic capacities were carried out. From 5 species of green and brown marine algae, 224 bacterial strains were isolated and tested for antibiotic production. A total of 38 strains displayed antibiotic activity, withEnteromorpha intestinalis being the source of the highest number of producer strains. All epiphytic bacteria with antibiotic activity were assigned to thePseudomonas-Alteromonas group. Antagonism assays among the isolates demonstrated that each producer strain inhibits the growth of the other producers, as well as of some nonproducer strains also isolated from seaweeds. Likewise, an autoinhibitory effect was observed in all antibiotic-producing strains. Antibacterial spectra of all the strains include activity againstStaphylococcus, Alcaligenes, Pseudomonas, Vibrio, Pasteurella, andAchromobacter. A preliminary characterization of the antibiotic substances produced by these epiphytic bacteria demonstrated that they are low molecular weight compounds, thermolabile, and anionic and are not affected by proteolytic enzymes. The role that these inhibitory substances can play in the natural environment is discussed.

The genus Tenacibaculum, a member of the family Flavobacteriaceae, is an abundant component of marine bacterial ecosystems that also hosts several fish pathogens, some of which are of serious concern for marine aquaculture. Here, we applied multilocus sequence analysis (MLSA) to 114 representatives of most known species in the genus and of the worldwide diversity of the major fish pathogen Tenacibaculum maritimum. Recombination hampers precise phylogenetic reconstruction, but the data indicate intertwined environmental and pathogenic lineages, which suggests that pathogenicity evolved independently in several species. At lower phylogenetic levels recombination is also important, and the species T. maritimum constitutes a cohesive group of isolates. Importantly, the data reveal no trace of long-distance dissemination that could be linked to international fish movements. Instead, the high number of distinct genotypes suggests an endemic distribution of strains. The MLSA scheme and the data described in this study will help in monitoring Tenacibaculum infections in marine aquaculture; we show, for instance, that isolates from tenacibaculosis outbreaks in Norwegian salmon farms are related to T. dicentrarchi, a recently described species.

We describe in this work a new iron uptake system encoded by chromosomal genes in pathogenic strains of Vibrio anguilarum. This iron uptake system differs from the plasmid-encoded anguibactin-mediated system present in certain strains of V. anguilarum in several properties. The siderophore anguibactin is not utilized as an external siderophore, and although characteristic outer membrane proteins are synthesized under iron-limiting conditions, these are not related to the plasinid-mediated outer membrane protein OM2 associated with ferric anguibactin transport. Furthermore, the siderophore produced by the plasmidless strains may be functionally related to enterobactin as demonstrated by bioassays with enterobactin-deficient mutants, although its behavior under various chemical treatments suggested major differences from that siderophore. Hybridization experiments suggested that the V. anguillarum chromosome-mediated iron uptake system is unrelated genetically to either the anguibactin or enterobactin-associated iron assimilation systems.One of the most important virulence factors in many pathogenic bacteria is the ability to utilize iron-from the host fluids by means of an efficient iron-sequestering system (5,8,18,22,34). Vibrio anguillarum is a bacterium highly pathogenic for different species of marine fish, causing the disease known as vibriosis (6,15,25). In strain 775, isolated from the Pacific Northwest coast of the United States, an iron uptake system is mediated by a 65-kilobase plasmid designated pJM1 (7,11,13). This system allows bacteria to grow at low concentrations of available iron imposed by the high-affinity iron-binding proteins present in the host fluids. Experimental infections demonstrated that possession of the pJM1 iron uptake genetic determinants is essential to cause disease (7,11,33,35).Genetic characterization of the pJM1-mediated iron uptake system allowed the location of the iron uptake genes to a 25-kilobase region of the pJM1 plasmid (12,29,33). These genes determine the synthesis of the two essential components involved in the iron uptake process: the diffusible siderophore anguibactin (1, 33) and a component of the receptor for the iron-siderophore complex identified as the 86-kilodalton outer membrane protein OM2 (2, 10). Other pathogenic strains of V. anguillarum isolated from cultured turbot on the northwestern Atlantic coast of Spain also harbor a plasmid which exhibits a high structural and functional homology with pJM1 (28). However, in recent studies with other virulent strains of V. anguillarum that were also iron uptake proficient, ho plasmids have been detected, suggesting that the iron uptake system of these strains must be chromosomally encoded (30).In the present work we report the characterization of this chromosome-mediated iron uptake system present in certain plasmidless strains of V. anguillarum. Our results indicate that this new system is different from the one encoded by the pJM1-like plasmids. * Corresponding author. MATERIALS AND METHODSBacterial strains. Th...

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The activity of antibiotic-producing marine bacteria was assayed against bacterial fish pathogens belonging to the genera Vibrio, Aeromonas, Pasteurella, Edwardsiella, Yersinia and Pseudomonas with the aim of evaluating the possible use of these marine strains for controlling epizootics in aquaculture. Inhibition tests on solid medium showed that, in general, the majority of fish bacteria were strongly sensitive to the marine bacteria. Only two strains (Edwardsiella tarda and Pseudomonas aeruginosa), were resistant to all the antibiotic-producing strains. The results of antagonism assays in sea water, however, varied according to the fish pathogens examined. Experiments conducted using cell-free supernatant fluids of marine bacteria demonstrated the involvement of antibiotic substances in the inhibition of fish pathogens.