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

Abstract

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-89 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 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.

New Zealand rickettsia‐like organism (NZ‐RLO) and Tenacibaculum maritimum: Distribution and phylogeny in farmed Chinook salmon (Oncorhynchus tshawytscha)

“…It is hypothesized that temperature plays a key role in the presence of NZ‐RLO. In vitro studies into the growth characteristics of NZ‐RLO1 and NZ‐RLO2 have determined these organisms grow best at 18°C (Gias et al., ). NZ‐RLO1 can grow in higher temperatures of 22°C, whereas NZ‐RLO2 will not grow above 18°C.…”

“…NZ‐RLO1 can grow in higher temperatures of 22°C, whereas NZ‐RLO2 will not grow above 18°C. (Gias et al., ). This in vitro work supports the findings of increased prevalence of NZ‐RLO1 and NZ‐RLO2 in the fish originating from sites where the water temperatures were the highest (>17°C) and a lower prevalence or no NZ‐RLO at sites with lower seawater temperatures (<15°C).…”

“…NZ-RLO1 can grow in higher temperatures of 22°C, whereas NZ-RLO2 will not grow above 18°C. (Gias et al, 2018). This in vitro work supports the findings of in- At sites 1 and 2, maximum summer temperatures routinely exceeded 17°C and in 2015 and were approximately 0.5°C higher than those reported in the previous years.…”

First description and diagnostics of disease caused by Piscirickettsia salmonis in farmed European sea bass (Dicentrarchus labrax Linnaeus) from Croatia

“…A similar condition was also observed in farmed pink salmon ( Oncorhynchus gorbuscha Walbaum 1792) and coho salmon in British Columbia, Canada, but without a high mortality rate (Brocklebank et al., 1992). There are other reports of salmonids infected with RLO from Ireland (Rodger & Drinan, 1993), Norway (Olsen et al., 1997), Scotland (Birrell et al., 2003), Australia (Corbeil et al., 2005) and New Zealand (Brosnahan et al, 2019; Gias et al., 2018). In all affected salmonid species, systemic disease was observed, with characteristic lesions in the liver (Almendras et al., 2000).…”