We present here the first evidence of the presence of iron uptake mechanisms in the bacterial fish pathogen Tenacibaculum maritimum. Representative strains of this species, with different serotypes and origins, were examined. All of them were able to grow in the presence of the chelating agent ethylenediamine-di-(o-hydroxyphenyl acetic acid) (EDDHA) and also produced siderophores. Cross-feeding assays suggest that the siderophores produced are closely related. In addition, all T. maritimum strains utilized transferrin, hemin, hemoglobin, and ferric ammonic citrate as iron sources when added to iron-deficient media. Whole cells of all T. maritimum strains, grown under iron-supplemented or iron-restricted conditions, were able to bind hemin, indicating the existence of constitutive binding components located at the T. maritimum cell surface. This was confirmed by the observation that isolated total and outer membrane proteins from all of the strains, regardless of the iron levels of the media, were able to bind hemin, with the outer membranes showing the strongest binding. proteinase K treatment of whole cells did not affect the hemin binding, indicating that, in addition to proteins, some protease-resistant components could also bind hemin. At least three outer membrane proteins were induced in iron-limiting conditions, and all strains, regardless of their serotype, showed a similar pattern of induced proteins. The results of the present study suggest that T. maritimum possesses at least two different systems of iron acquisition: one involving the synthesis of siderophores and another that allows the utilization of heme groups as iron sources by direct binding.
Tenacibaculum maritimum (formerly Flexibacter maritimus)(48) is the etiological agent of an ulcerative disease known as marine flexibacteriosis or tenacibaculosis, which affects a large number of marine fish in the world and thus has considerable economic significance to aquaculture producers. The infection has diverse clinical manifestations depending on the species and age of fish, the most significant symptom being the presence of gross lesions on the body surface (11,16).Although the phenotypic, antigenic, and molecular characteristics of T. maritimum have been examined by several authors (for a review, see reference 49), the actual factors determining the virulence of this pathogen have not yet been elucidated. Some synergistic interactions of the toxins contained in extracellular products and a hemolysin might be involved in T. maritimum infections (8). Moreover, pathological properties of the bacterium, such as a strong adherence to the skin mucus of different fish species and the capacity to resist its bactericidal activity (31), have been pointed out as possible virulence factors.It is well known that the ability to take up iron during infection is an essential factor in the pathogenicity of several bacteria, being necessary for the pathogen multiplication. However, the levels of free iron in the biological fluids within the animal host is often v...