Iron acquisition and siderophore production in the fish pathogen Renibacterium salmoninarum

Abstract

Renibacterium salmoninarum is the causative agent of bacterial kidney disease, which significantly affects salmonid farming worldwide. Despite this impact, there is scarce data on its iron uptake ability, a factor of pathogenesis. This study investigated the iron acquisition mechanisms of R. salmoninarum and its capacity to uptake iron from different sources. Thirty-two Chilean isolates and the DSM20767 type strain grew in the presence of 2,2'-Dipyridyl at varying concentrations (250-330 μm), and all isolates positively reacted on chrome azurol S agar. Subsequently, inocula of four Chilean isolates and the type strain were prepared with or without 200 μm of 2,2'-Dipyridyl for uptake assays. Assay results revealed differences between the isolates in terms of iron acquisition. While a prior iron-limited environment was, for most isolates, not required to activate the uptake of iron (II) sulphate, ammonium iron (III) citrate or iron (III) chloride at higher concentrations (100 μm), it did facilitate growth at lower iron concentrations (10 μm and 1 μm). An exception was the H-2 isolate, which only grew with 100 μm of iron sulphide. In turn, 100 μm of haemin was toxic when isolates were grown in normal KDM-2. In silico R. salmoninarumATCC 33209 genome analysis detected various genes coding iron uptake-related proteins. This is the first study indicating two iron acquisition systems in R. salmoninarum: one involving siderophores and another involving haem group utilization. These data represent a first step towards fully elucidating this virulence factor in the pathogenic R. salmoninarum.

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.…”

LPS Modulates the Expression of Iron-Related Immune Genes in Two Antarctic Notothenoids

“…In the present study fish were injected twice, at 0 and 48 h, and sampled at 120 h after the last injection, a design chosen taken in consideration that low temperature habitats may contribute to a slower innate immune system response, as it has been described in cold-water fish when compared to temperate fish (Tort et al, 2003;MacKenzie et al, 2008;Magnoni et al, 2015;Bonneaud et al, 2016;Chen et al, 2016;Abram et al, 2017;Martínez et al, 2017a). The overall gene expression response, albeit not as vigorous as in other vertebrates (Collins, 2008;Johnson and Wessling-Resnick, 2012;Bethke et al, 2016), also suggests that an iron related immune response is active, much alike what it was seen in the sub-Antarctic Notothenioid Eleginops maclovinus (Martínez et al, 2017a), the Senegalese sole, Solea senegalensis (Prieto-Álamo et al, 2009) or the roughskin sculpin, Trachidermus fasciatus (Liu et al, 2012), among other fish species.…”

“…Proinflammatory cytokines such as IL-6 stimulate the transcription of hepcidin, triggering and potentiating the hypoferric response of inflammation (Nemeth et al, 2004a). Several bacterial pathogens obtain the iron they need for their survival and replication from an external source (Ratledge and Dover, 2000;Pulgar et al, 2015;Bethke et al, 2016Bethke et al, , 2018Calquín et al, 2018). For this reason, eukaryotic organisms must effectively control iron homeostasis, through the regulation of the proteins involved in its metabolism (Skaar, 2010).…”

Addressing viral and bacterial threats to salmon farming in Chile: historical contexts and perspectives for management and control

“…iron uptake mechanisms) were just published in 2016 (Bethke et al . ). When taken together with there being only one registered vaccine for the prevention of BKD in Chile with a varied effectiveness in field conditions, the necessity of obtaining basic information on the causal pathogen for BKD, that is R. salmoninarum , becomes paramount.…”

“…iron restriction) (Bethke et al . , ). This 22 kDa protein could play an important role during infection and disease development and has immunosuppressive and agglutination properties even more effective than p57 (Fredriksen et al .…”