Dominique Chagot

Separation of Crassostrea gigas hemocytes by density gradient centrifugation and counterflow centrifugal elutriation.

A protocol is described to separate several subpopulations of hemocytes in a unique medium which avoids cell aggregation and retains cell-viability. Isopycnic centrifugation in Percoll followed by counterflow centrifugal elutriation provides large quantities of separated granulocyte and hyalinocyte subpopulations.

Isolation and purification of the protozoan Bonamia ostreae (Pichot et al. 1980), a parasite affecting the flat oyster Ostrea edulis L.

The isolation and purification of Bonamia ostreae (Ascetospora), an intrahemocytic protozoan parasite of Ostrea edulis, have been achieved according to an original protocol. The purified cells showed good retention of infectivity and ultrastructural morphology. They could also be used to prepare specific immune sera for indirect immunofluorescence.

Interactions between Bonamia ostreae (Protozoa: Ascetospora) and hemocytes of Ostrea edulis and Crassostrea gigas (Mollusca: Bivalvia): Entry mechanisms

Entry mechanisms of the intrahemocytic parasite Bonamia ostreae (Ascetospora) into hemocytes of the sensitive (Ostrea edulis) and a resistant (Crassostrea gigas) oyster species have been analyzed. The study was based upon the development of a B. ostreae-hemocyte in vitro system. Ultrastructural features and Cytochalasin B sensitivity of the phenomenon demonstrate that B. ostreae enters into the two oyster species hemocytes by host-specified phagocytosis, although parasite contribution to entry into O. edulis hemocytes cannot be discarded. Possible receptors and the postphagocytic fate of the parasite are discussed.

Interactions between Bonamia ostreae (Protozoa: Ascetospora) and hemocytes of Ostrea edulis and Crassostrea gigas (Mollusca: Bivalvia): in vitro system establishment

Abstract Based on parasite purification and hemocyte primary culture, an in vitro system was established for studying early interactions between Bonamia ostreae and the hemocytes of sensitive Ostrea edulis and resistant Crassostrea gigas. Infections were observed whichever the hemocytic types and the oyster species. The advantages and disadvantages of the system are discussed with regard to the study of recognition, entry, and survival mechanisms of the parasite.

Histological study of a cellular reaction in Ruditapes decussatus infected by a protozoan

An infection caused by a Perkinsus -like parasite has been observed in Ruditapes decussatus from Portugal (Comps and Chagot, 1987). Following a pathological study carried out on clams affected by mortalities in the Algarve area, this parasite was found again, inducing a reaction process in the host. Histological examination reveals the parasite in the connective tissue of different organs. The adjoining tissues, particularly the epithelia, are not affected.

An infection of Ruditapes decussatus (Bivalvia) by Rickettsia

The authors report the presence of a Rickettsia in Ruditapes decussatus from natural populations of the Algarve (Portugal). Light microscopic shows infections of varying importance in gill tissues. Some enclose small procaryotic colonies (cp) scattered in all lamellae; in others, the colonies are scarce and hypertrophic (100 mu m). These different pictures suggest an amplification process. Digestive diverticulae may also be infected, but to a lesser extent. The ultrastructural features of this intravacuolar (mvd: densified vacuolar membrane) procaryote (P) and its multiplication by scission without a complex developmental cycle allows its classification in the order Rickettsiales.

Ultrastructural study of sporulated instars of a haplosporidian parasitizing the clam Ruditapes decussatus

In 1951, Vilela pointed out the presence of a haplosporidian parasitizing Ruditapes decussatus from Portuguese waters and created the species Haplosporidium tapetis. Later, a haplosporidian was found in the same species originating from the pound of Thau (France).

Study of a haplosporidian (Ascetospora), parasitizing the Australian flat oyster Ostrea angasi

Considering the epizootics which affect the French stock of flat oysters, Ostrea edulis (Grizel, 1985), trials to introduce an Australian oyster, Ostrea angasi, have been undertaken. The spat produced in a hatchery from breeders imported from Australia were reared in the south ofBrittany and in Normandy (Bougrier et al., 1986). Following mass mortalities (65% of individuals) a haplosporidian was observed in this species. Sporogenesis of the parasite was studied using Iight and electron microscopy.