Iron acquisition and siderophore production in the fish pathogen Renibacterium salmoninarum

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(T) type strain grew in the presence of 2,20-Dipyridyl at varying concentrations (250330 mu M), 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 mu M of 2,20-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 mu M), it did facilitate growth at lower iron concentrations (10 mu M and 1 mu M). An exception was the H-2 isolate, which only grew with 100 mu M of iron sulphide. In turn, 100 mu M of haemin was toxic when isolates were grown in normal KDM-2. In silico R. salmoninarum ATCC 33209 T 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.