Scanning electron microscopic observation of the in vitro cultured protozoan, Perkinsus olseni, isolated from the Manila clam, Ruditapes philippinarum

Dinesh Gajamange,Kyung-Il Park,Carlos Azevedo,Seung-Hyeon Kim,Kwang-Sik Choi

doi:10.1186/s12866-020-01926-0

Abstract

BackgroundPerkinsosis 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).ResultsThe 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.ConclusionsOur morphological and ultrastructural studies contribute new information on the life cycle and propagation of P. olseni.

Highlights

Perkinsosis is a major disease affecting the commercially important marine mollusk Ruditapes philippinarum (Manila clam) in Asian waters
This new parasite species has been described in Manila clams from Japan and in R. variegatus collected on Jeju Island, on the southern coast of Korea, after a nation-wide survey of P. honshuensis: P. honshuensis specific primers were used to screen clams from 23 different locations [13,14,15]
On the second day of in vitro culture, prezoosporangia were spherical, as observed under light microscope (LM) (Fig. 1a), which was consistent with the electron microscope observation showing that prezoosporangia have a smooth body wall (Fig. 1b)

Summary

Introduction

Perkinsosis is a major disease affecting the commercially important marine mollusk Ruditapes philippinarum (Manila clam) in Asian waters. 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 [1,2,3,4]. When trophozoites are exposed to anaerobic conditions, they grow larger and transform into thick-walled cells This phenomenon was confirmed by incubating host tissue infected with Perkinsus spp. in liquid RFTM [1, 23]. The zoosporangia release motile zoospores into the medium via the discharge tube [16] Zoospores gradually lose their zoospore characteristics, such as flagella and body shape, and transform into immotile trophozoites [27]. They develop into schizonts and release multiple daughter cells called merozoites [28]

Methods

Results

Conclusion