Pathogenicity of two <i>Candidatus</i> Xenohaliotis californiensis genetic variants against three abalone species (the genus <i>Haliotis</i>)

Abstract

For half a century, Japan has practiced marine stock-enhancement programs that aim to preserve or enhance natural fisheries resources. Currently, juveniles of about 70 marine species are produced in national and prefectural hatcheries, and released annually into the wild (Fisheries Research Agency, 2015a). Because of their high market value, abalone (Haliotidae) are particularly important coastal fishery resources; 30 Japanese governmental entities (city or prefectural governments) currently produce and release the juveniles to enhance stock (Fisheries Research Agency, 2015b). ABSTRACT Candidatus Xenohaliotis californiensis, a Rickettsia-like organism (RLO) that causes 'withering syndrome' (WS) in abalone, has been recently detected in Japan. We analyzed partial nucleotide sequence (113 bp) of 16S rRNA of WS-RLOs (n = 335) from Japanese black abalone Haliotis discus discus, Ezo abalone H. discus hannai, giant abalone H. gigantea, tokobushi abalone H. diversicolor aquatilis and fukutokobushi abalone H. diversicolor diversicolor. All the sequences from Japanese black, Ezo and giant abalone were identical, but different from those from tokobushi and fukutokobushi at one nucleotide position. We also conducted cohabitation challenge to determine whether the WS-RLO in fukutokobushi infects Japanese black and giant abalone or the agent in Japanese black abalone infects fukutokobushi. Twenty fukutokobushi naturally infected with WS-RLO were cohabited with 10 healthy individuals of each of Japanese black, giant, and fukutokobushi abalone for a total of 84 days. At the end of the experiment, surviving fukutokobushi abalone were positive in PCR test for WS-RLO, but negative for that of Japanese black and Ezo abalone. In the reverse combination experiment, in which naturally infected Japanese black abalone were cohabited with these three species, WS-RLO transmissions were found in Japanese black and Ezo, but not in fukutokobushi abalone. These results suggest that two genetic variants of WS-RLO have a different host specificity.

Diseases of Gastropoda

“…Rickettsial infections in Haliotis diversicolor supertexta ( 17 ), caused similar symptoms, but symptoms and mortality only occurred at water temperatures of 30°C. ( 18 ) also showed that at least 2 genetic variants show a different host specificity. Vibrio parahaemolyticus has also been isolated from H. diversicolor supertexta in Taiwan showing signs of withering syndrome ( 19 , 20 ).…”

Rickettsiales‐like organisms in bivalves and marine gastropods: a review

“…While other abalone species like H. fulgens and H. corrugata are more resistant (Álvarez Tinajero et al, 2002; Moore et al, 2009; Cruz‐Flores et al, 2016). Cohabitation studies of infect abalone species by two genetic variants of C Xc in Japan showed that these variants have different host specificity (Nishioka et al, 2016). This might also be the case for other RLOs capable of infecting different mollusc species, where the RLO could act as harmless symbiont in one species and be highly pathogenic for other species.…”

“…The first Rickettsiales‐like organism from a marine mollusc was described in the soft shell clam Mya arenaria in 1977 by Harshbarger and Chang, (1977); since then, over 60 species of marine bivalve mollusc, one species of freshwater clam ( Rangia flexuosa ), one species of fresh water mussel ( Dreissena spp.) and at least ten gastropod species have been reported to harbour these organisms (Nishioka et al, 2016 and see Table 1 for more references). Rickettsiales‐like organisms (RLOs) are small intracellular prokaryotes that are generally found within intracytoplasmic vacuoles (IVs) in numerous tissues of bivalve and gastropod molluscs of fishery and aquaculture importance.…”