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

Abstract

This study characterizes intracytoplasmic infections with prokaryote microorganisms in Dreissena sp. (near Dreissena polymorpha) from northeastern Greece and represents the first report of such infections in freshwater bivalves. Light microscope observations of stained tissues revealed basophilic, cytoplasmic inclusion bodies in 87.5% (28/32) of the mussels sectioned. Inclusions in epithelial cells and connective tissues were noted, respectively, in 34.4 and 71.9% of the sample, with 5 mussels (15.6%) having both tissue types infected. Epithelial cell infections were observed in histological sections only in digestive gland tubules and ducts; within tubules, inclusions were present more often in secretory than digestive cells. Connective tissue infections, however, were systemic; among the 32 mussels sectioned, inclusions were found in the gills (65.6%), foot (12.5%), mantle (9.4%), labial palps (6.3%), digestive gland (6.3%), stomach (6.3%), and gonads (3.1%). Cytoplasmic inclusions (maximum dimension, 138 µm) were prominent enough in the gills to be visible in 17.0% of the 247 mussels dissected. Ultrastructurally, prokaryote cells in gill connective tissues were clearly characteristic of Chlamydiales-like organisms, with each intracytoplasmic inclusion containing a loosely packed mixture of elementary, reticulate, intermediate bodies, and blebs. Prokaryote colonies in digestive gland epithelial cells exclusively contained 1 of 4 morphological cell types and were considered Rickettsiales-like. Hexagonal, virus-like particles were present in the cytoplasm of the largest of these Rickettsiales-like prokaryotes. Although host stress was evident from localized cell necrosis and dense hemocyte infiltration, overall infection was fairly benign, with no major, adverse impact on body condition evident among sectioned or dissected mussels. A possible negative effect was partial constriction of gill water tubes, but at the infection intensity observed (typical range 1 to 7 inclusion bodies per section), significant interference with respiration and other metabolic functions of the gills was highly unlikely.

Prevalence of parasites in amphipods Diporeia spp. from Lakes Michigan and Huron, USA

“…data). Zebra mussels have been reported with rickettisia-like and chlamydia-like infections from Greece (Molloy et al 2001), and a putatively lethal infection of a haplosporidian protozoan was reported in zebra mussels from The Netherlands (Bowmer & Van der Meer 1991, Molloy et al 1997. The relationship, if any, between parasite infections in the zebra mussel and amphipods is unknown.…”

The effects of the trematode Bucephalus polymorphus on the reproductive cycle of the zebra mussel Dreissena polymorpha in the Drava River

“…However, investigations of diversity, distribution and significance of endoparasites of D. polymorpha have become important only during the past decade. These studies include Dreissena's mantle-cavity ciliates (Laruelle et al 1999, intracytoplasmic prokaryotes (Molloy et al 2001) and endosymbiont assemblages detected in Dreissena populations in Russia (Kuperman et al 1994, Molloy et al 1996 and Belarus .…”

Seasonal dynamics of zebra mussel parasite populations

“…A semiquantitative parasite inventory was made by observing 30 to 40 tissue sections per mussel, and parasites were identified following Molloy et al (1997Molloy et al ( , 2001Molloy et al ( , 2005. The level of infection was assessed using standard epidemiological parameters (Bush et al 1997): prevalence (percentage of mussels infected) and mean intensity (mean number of parasites per infected mussel) only for parasites that could be enumerated, i.e.…”

“…and Spheno phrya dreissenae), (2) intracellular bacteria (Rickettsiales-like organisms [RLOs]), and (3) 3 tre ma tode species, Phyllodistomum folium, Bu cepha lus polymor phus and Echinopary phium sp. (Molloy et al 1997(Molloy et al , 2001(Molloy et al , 2005.In the framework of environmental parasitology, a better understanding of interactions between parasite species and host is necessary. However, these interactions are poorly documented in the freshwater zebra mussel, in contrast with other invertebrate species presenting an economic interest.…”