Scanning electron microscopic observation of the in vitro cultured protozoan, Perkinsus olseni , isolated from the Manil
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RESEARCH ARTICLE
Open Access
Scanning electron microscopic observation of the in vitro cultured protozoan, Perkinsus olseni, isolated from the Manila clam, Ruditapes philippinarum Dinesh Gajamange1,2, Seung-Hyeon Kim1, Kwang-Sik Choi3, Carlos Azevedo4 and Kyung-Il Park1*
Abstract Background: Perkinsosis is a major disease affecting the commercially important marine mollusk Ruditapes philippinarum (Manila clam) in Asian waters. In this study, we investigated the morphological characteristics of Perkinsus olseni, the causative agent of perkinsosis, cultured under laboratory conditions at different stages of its life cycle using a scanning electron microscope (SEM). Results: The prezoosporangia formed after induction with Ray’s fluid thioglycollate medium (RFTM) developed into zoosporangia. During this process, a discharge tube formed a porous sponge-like structure that detached before the zoospores were released; thus, this organelle operated as a bung. Liberated zoospores gradually transformed into immature trophozoites, during which detachment of the anterior flagella occurred, but the loss of the posterior flagella was not clearly observed in the present study. Mature trophozoites underwent schizogony by cleaving the cell forming some merozoites in schizonts, which were released by the rupturing of the cellular membrane of the schizont within a few days. Conclusions: Our morphological and ultrastructural studies contribute new information on the life cycle and propagation of P. olseni. Keywords: Perkinsus olseni, life cycle, Manila clam, Morphology, SEM
Background Perkinsus olseni is a parasitic protozoan and is the causative agent of perkinsosis in the Manila clam (Ruditapes philippinarum), which is found in tidal flats and sandy beaches along the coasts of Asia and Europe [1–4]. The Manila clam found in Korean waters is an important edible shellfish of the mariculture industry; however, recurrent mass mortalities of this species have significantly impacted mariculture production [5]. Histopathological * Correspondence: [email protected] 1 Department of Aquatic Life Medicine, College of Ocean Science and Technology, Kunsan National University, 558 Daehakno, Gunsan 54150, Republic of Korea Full list of author information is available at the end of the article
studies have reported that severe inflammatory reactions can occur in the connective tissue of the gonad, gills, mantle, stomach, and digestive gland due to severe P. olseni infections that could have deleterious effects on reproductive efforts and food digestion [6–8]. It was reported that the recent summer mortality of Manila clams on the west coast of Korea was caused by the combined effects of P. olseni infection and thermal stress [9]. In Japan, the negative effects of P. olseni on the survival of wild clam populations in Ariake Bay were also reported [10]. Since the first occurrence of P. olseni in Manila clams in Asia, described in the late 1990s by molecular studies
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