Ultrastructural description of new Rickettsia-like organisms in the commercial abalone Haliotis tuberculata (Gastropoda: Haliotidae) from the NW of Spain

Abstract

Rickettsia-like organisms (RLOs) were found in the commercially farmed abalone Haliotis tuberculata in the northwestern region of the Atlantic Coast of Spain and are described from light and transmission electron microscopy observations. The RLOs measured ~1.6 × 0.9 µm and were found in intracytoplasmic, spherical to ellipsoidal vacuoles (up to 8 µm) in the epithelial cells of the digestive diverticulae. The morphological ultrastructure of these organisms was typically prokaryotic, including a plasmalemma and a thin Gram-negative type cell wall. Several ultrastructural changes were observed in the epithelial cells of the host containing the RLOs. The nuclei became pycnotic and several basophilic dense inclusions appeared in the cytoplasm. In addition, the host cell appeared lysed and was ruptured in advanced stages of infection. It was impossible to ascertain whether the RLOs are responsible for this disease, as a haplosporidian infection was also present. We can only conclude that the presence of RLOs simultaneously with a haplosporidian parasite may contribute to the mortality of the abalone host.KEY WORDS: Ultrastructure · Rickettsia-like organisms · Abalone · Spain Resale or republication not permitted without written consent of the publisherDis Aquat Org 71: [233][234][235][236][237] 2006 cultured and natural populations of Haliotis spp. from different geographic areas (Antonio et al. 2000, Bower 2004. Recently, the syndrome has been described as a severe pathogen-caused disease associated with Rickettsiales-like prokaryotes (Haaker et al. 1992, Gardner et al. 1995, Antonio et al. 2000, Bower 2004, Braid et al. 2005.The purpose of this work is to document and describe the ultrastructure of RLOs found in abalone Haliotis tuberculata. These prokaryotic parasites may contribute to the mortality of this commercially important species. MATERIALS AND METHODSJuvenile abalone Haliotis tuberculata (Linnaeus, 1758) (Gastropoda: Haliotidae) from Ireland were grown in barrels suspended from rafts in El Grove, Galicia, NW of Spain (42°29' 20'' N, 08°53' 56'' W). Fifteen specimens were observed by light microscopy (LM) during a study which aimed to identify haplosporidiosis. In addition to the haplosporidian parasite, some of the specimens were also found to be parasitized by RLOs, mainly in the epithelial cells of the digestive diverticulae.Small fragments of the parasitized tissues were fixed in 3% glutaraldehyde in 0.2 M sodium cacodylate buffer pH 7.2 for 10 h at 4°C, washed overnight in the same buffer at 4°C, and post-fixed in buffered 2% OsO 4 for 3 h at 4°C. After dehydration in an ascendant ethanol series followed by propylene oxide, the tissues were embedded in Epon. Semithin sections were stained with methylene blue-Azur II and observed under differential interference contrast (DIC; Nomarski) microscopy. For transmission electron microscopy (TEM), the tissues were ultrathin-sectioned with a diamond knife, double-stained with uranyl acetate and lead citrate and observed in a JEOL 100CXII TEM operat...

“Candidatus Cryptoprodotis polytropus,” A Novel Rickettsia‐Like Organism in the Ciliated Protist Pseudomicrothorax dubius (Ciliophora, Nassophorea)

“…Unfortunately, a proper molecular characterization is available only for a few RLOs. The importance of RLOs is actually increasing as they are now recognized as aetiological agents of mass disease outbreaks involving cultivated species of commercial interest, such as molluscs (Azevedo et al 2006; Delgado et al 2007; Friedman et al 2000; Moore et al 2002; Sun and Wu 2004; Wu and Pan 1999), crustaceans (Eddy et al 2007; Edgerton and Prior 1999; Edgerton et al 2004; Loy et al 1996; Nunan et al 2003; Wang and Gu 2002), and fishes (for recent reports, see Arkush et al 2005; Corbeil, Hyatt, and Crane 2005; Mauel et al 2005; Timur et al 2005). Unlike the rickettsiae (gen. Rickettsia ), which are typically associated with arthropods that may act either as vectors or primary hosts, and often display a multiple host life cycle (Yu and Walker 2005), RLOs infecting aquatic organisms can probably be horizontally transmitted without the requirement of a vector (Athanassopoulou et al 2004; Edgerton et al 2002; Fryer and Lannan 2005; Smith et al 1999).…”

Bacteria-Affecting Cephalopods

“…RLO are gram-negative bacteria, which have been associated with infection and mass mortalities in several aquatic animals. Particularly, cases of molluscs bivalves have increased since the first description in clams was reported (Azevedo et al 2006; revised by Romalde and Barja 2010; Ceuta and Boehs 2012; revised by Gollas-Galván et al 2014). These organisms have been found mainly within the epithelial cells of the mantle, gills digestive gland, connective tissue and hepatopancreas of several molluscs (revised by Gollas-Galván et al 2014).…”

Gene expression patterns of abalone, Haliotis tuberculata, during successive infections by the pathogen Vibrio harveyi

“…During the past decade, disease outbreaks in both farmed and wild populations of European abalone, Haliotis tuberculata, have been associated with emerging protistan (Azevedo et al, 2006a;Balseiro et al, 2006) and bacterial parasites (Azevedo et al, 2006b;Balseiro et al, 2006;Nicolas et al, 2002). Declines in European stocks of abalone have coincided with emergence of these pathogens (Huchette and Clavier, 2004).…”