Abstract
A rickettsia‐like organism, designated NZ ‐ RLO 2, was isolated from Chinook salmon ( Oncorhynchus tshawytscha ) farmed in the South Island, New Zealand. In vivo growth showed NZ ‐ RLO 2 was able to grow in CHSE ‐214, EPC , BHK ‐21, C6/36 and Sf21 cell lines, while Piscirickettsia salmonis LF ‐89 T grew in all but BHK ‐21 and Sf21. NZ ‐ RLO 2 grew optimally in EPC at 15°C, CHSE ‐214 and EPC at 18°C. The growth of LF ‐89 T was optimal at 15°C, 18°C and 22°C in CHSE ‐24, but appeared less efficient in EPC cells at all temperatures. Pan‐genome comparison of predicted proteomes shows that available Chilean strains of P. salmonis grouped into two clusters ( p‐ value = 94%). NZ ‐ RLO 2 was genetically different from previously described NZ ‐ RLO 1, and both strains grouped separately from the Chilean strains in one of the two clusters ( p ‐value = 88%), but were closely related to each other. TaqMan and Sybr Green real‐time PCR targeting RNA polymerase (rpoB) and DNA primase (dnaG), respectively, were developed to detect NZ ‐ RLO 2. This study indicates that the New Zealand strains showed a closer genetic relationship to one of the Chilean P. salmonis clusters; however, more Piscirickettsia genomes from wider geographical regions and diverse hosts are needed to better understand the classification within this genus.