Iron assimilation and siderophore production by Vibrio ordalii strains isolated from diseased Atlantic salmon Salmo salar in Chile

Abstract

Vibrio ordalii is the causative agent of vibriosis in several cultured salmonid species worldwide. Despite its impact on aquaculture, relatively little information is available about its virulence factors. The present study demonstrates for the first time that V. ordalii possesses different systems of iron acquisition, one involving siderophore synthesis and another one that uses direct binding of heme to use iron. Using 6 strains of V. ordalii from Atlantic salmon Salmo salar and the V. ordalii type strain, we could demonstrate that all strains could grow in presence of the chelating agent 2,2'-dipyridyl and produced siderophores in solid and liquid media. Cross-feeding assays among V. ordalii strains evidenced variability in the siderophores produced. Bioassays and PCR data suggest that V. ordalii could produce a siderophore with a structure similar to piscibactin, although the production of a second siderophore in certain strains cannot be discarded. Furthermore, all strains were able to use hemin and hemoglobin as the only iron sources, although the cell yield was higher when using hemoglobin. A hemin-binding assay indicated the presence of constitutive heme-binding molecules at the cell surface of V. ordalii. Virulence tests using rainbow trout as a model of infection revealed a clear relationship between iron-uptake ability and pathogenicity in V. ordalii.

Physiological evidence that Piscirickettsia salmonis produces siderophores and uses iron from different sources

“…Furthermore, similar growth values were obtained independent of concentrations (e.g., 400 vs. 1,000 μmol/L) or iron source (i.e., ferric ammonium citrate vs. ferric nitrate). These observations indicate that P. salmonis can grow with either of the evaluated iron sources, a finding in line with reports for other pathogenic microorganisms in fish (Bethke, Poblete‐Morales, Irgang, Yáñez, & Avendaño‐Herrera, ; Ruiz et al., ). The difficulty of culturing P. salmonis is also worth noting.…”

“…Briefly, each P. salmonis isolate (10 μl, grown in AUSTRAL‐SRS broth) was spotted onto CAS agar in two independent experiments. Vibrio ordalii ATCC 33509 T was used as a positive control (Ruiz et al., ). Siderophore production on CAS agar was expressed as the ratio between the diameter of the orange halo and the diameter of bacterial growth after 10 days of incubation at 18°C.…”

Evidence for the facultative intracellular behaviour of the fish pathogen Vibrio ordalii

“…Two representative strains of V. ordalii were selected: Vo-LM-18, isolated from Atlantic salmon, and ATCC 33509 T , the type strain. Both have been used in previous studies (Ruiz et al, 2015(Ruiz et al, , 2016. The identity of each strain was confirmed as V. ordalii by standard phenotypical procedures (Silva-Rubio, Acevedo, et al, 2008a) and using the PCR-based analysis described by Avendaño-Herrera et al (2014).…”

Identification and characterization of outer membrane vesicles from the fish pathogen Vibrio ordalii

“…This intracellular behaviour was previously reported in V. ordalii through the use of flow cytometry, with results concluding that this bacterium can survive for 8 hours in the CHSE‐214 cell line without causing damage, suggesting pathogenicity mechanisms not yet elucidated for the Vibrio genus (Avendaño‐Herrera et al, 2019; Hong et al, 2009). Genes likely associated with adhesion, colonization and invasion factors; exotoxin production; cell surface components; and iron uptake systems have also been identified in V. ordalii (Naka, López, & Crosa, 2008; Ruiz et al, 2016). Most of these mechanisms have been evidenced through physiological studies (Ruiz et al, 2015, 2016).…”

“…Genes likely associated with adhesion, colonization and invasion factors; exotoxin production; cell surface components; and iron uptake systems have also been identified in V. ordalii (Naka, López, & Crosa, 2008; Ruiz et al, 2016). Most of these mechanisms have been evidenced through physiological studies (Ruiz et al, 2015, 2016).…”