In vivo growth and genomic characterization of rickettsia‐like organisms isolated from farmed Chinook salmon (Oncorhynchus tshawytscha) in New Zealand

• Published in: Journal of fish diseases Vol. 41; no. 8; pp. 1235 - 1245
• Main Authors: Gias, E, Brosnahan, C L, Orr, D, Binney, B, Ha, H J, Preece, M A, Jones, B
• Format: Journal Article
• Language: English
• Published: England Blackwell Publishing Ltd 01.08.2018
• Subjects: Cell lines; Chinook salmon; Clusters; Deoxyribonucleic acid; DNA; DNA primase; DNA-directed RNA polymerase; Fish; Freshwater fishes; Genetic relationship; Genomes; Growth; in vivo growth; Nucleic acids; Nucleotide sequence; Oncorhynchus tshawytscha; Optimization; pan‐genome; PCR; Piscirickettsia salmonis; Primase; Ribonucleic acid; rickettsia‐like organism; RNA; RNA polymerase; RpoB protein; Salmon; Strains (organisms); New Zealand; Piscirickettsia salmonis; in vivo growth; pan-genome; rickettsia-like organism; Chinook salmon
• ISSN: 0140-7775; 1365-2761
• DOI: 10.1111/jfd.12817

A rickettsia‐like organism, designated NZ‐RLO2, was isolated from Chinook salmon (Oncorhynchus tshawytscha) farmed in the South Island, New Zealand. In vivo growth showed NZ‐RLO2 was able to grow in CHSE‐214, EPC, BHK‐21, C6/36 and Sf21 cell lines, while Piscirickettsia salmonis LF‐89T grew in all but BHK‐21 and Sf21. NZ‐RLO2 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‐RLO2 was genetically different from previously described NZ‐RLO1, 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‐RLO2. 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.