Cytological studies on a new species of rickettsia found in association with a phage in the digestive gland of the marine bivalve mollusc, Tellina tenuis (da Costa)

Abstract

The secretory cells of the digestive glands of up to 75% of Tellina tenuis from sheltered sandy heaches on the Scottish coast contained intracytoplasmic inclusion bodies consisting of microcolonies of a rickettsia-like organism. The development and morphology of these parasitic bacteria and the cytopathic effect on the host cells are described. These features closely resemble those of the genus Coxiella of the family Rickettsiaceae. It was possible to culture the organism in embryonated hens' eggs. Scattered particles and paracrystalline arrays of a virus were seen in association with the bacteria. This is believed to be the first description of a phage from a rickettsia.

Characterization of intracytoplasmic prokaryote infections in Dreissena sp. (Bivalvia: Dreissenidae)

“…These reports also noted that prokaryote cells containing such virus-like particles, like our Type IV cells, were larger than uninfected cells and were likely a terminal phase in the prokaryote's life cycle, with host cells eventually lysing. Mean diameters of these virus-like particles in bivalves have ranged from 41 nm (Wen et al 1994) to 67 nm (Buchanan 1978), and thus the virus-like particles we observed (mean diameter, 45 mm) were relatively small and similar in size to those observed by Comps & Tigé (1999) in Mytilus galloprovincialis. Each particle had a hexagonal outline (Fig.…”

“…We did not observe these clear zones in our TEM observations, and thus they were probably an artifact of histological processing. Similar clear zones have also been present in paraffin sections of prokaryote infections in marine bivalves (Comps et al 1977, Buchanan 1978.…”

“…Considering that typically only 4 sections per mussel were examined, it is highly likely that even histological analysis underestimated true infection prevalence. A wide range of prevalences with intracytoplasmic prokaryotes occur in marine bivalves, including similar extensive infections, e.g., ca 100% by both Gulka & Chang (1984) and Le Gall et al (1991), > 85% by Johnson & Le Pennec (1995), and ≤ 75% by Buchanan (1978).…”

“…We observed intracytoplasmic prokaryotes in both digestive and secretory cells of the digestive gland epithelium. This is unusual since such infections in the digestive gland of marine bivalve populations have been almost always limited to either the digestive (Meyers 1979, Elston & Peacock 1984, Robledo et al 1994 or secretory cells (Buchanan 1978, Comps & Raimbault 1978). The only exception we are aware of is a population of the littoral bivalve Loripes lucinalis in Brest, France, in which both digestive gland cell types were observed infected (Herry et al 1994, Johnson & Le Pennec 1995.…”

“…Records of such hyperparasitism include both Rickettsiales-like (Buchanan 1978, Wen et al 1994, Comps & Tigé 1999 and Chlamydiales-like organisms , Meyers 1979, Johnson & Le Pennec 1995. These reports also noted that prokaryote cells containing such virus-like particles, like our Type IV cells, were larger than uninfected cells and were likely a terminal phase in the prokaryote's life cycle, with host cells eventually lysing.…”