Ultrastructural Observations on the Development of the Microsporidian Protozoon Plistophora hyphessobryconis Schaperclaus*

Abstract

SYSOPSIS.A sequence of developmental stages of Plistophora hyphessobryconis Schaperclaus, a microsporidian protozoan parasite of the muscular tissue of several species of freshwater fishes, was studied with the electron microscope. The youngest stages observed, ca. 4 X 2 p , have a single nucleus and their plasm contains only ergastoplasmic lamellae and ribosomes. They are surrounded by a halo of lysed host tissue. They increase in volume to become large sporonts with a great number of nuclei and a thick, 2-layered membrane. Thru schizogony, a corresponding number of sporoblasts is produced within this pansporoblast membrane. Sporoblasts start to develop a thick spore membrane, and a number of smoothmembraned vesicles appear in the plasm. These vesicles fuse to make the outer membrane of the filament. Later, its inner structures originate-the axial eleotron-dense substance, filling the hollow lumen ENEWED interest in the cytology of protozoan species R assignable to the class Microsporidea is reflected in the recent series of papers dealing with the fine structure of their spores ( 1,7,9,12,13,(15)(16)(17). Thanks to these studies on several types of microsporidian spores, their essential components are known: a shell composed of several layers; a. coiled polar filament whose basal part is joined with the apolar cap at the anterior pole of the spore; an anteriorly located swelling organelle, the polaroplast ; a fluid-filled vacuole at the posterior end of the spore; and, finally, the sporoplasm itself. An explanation of the role these organelles )lay during filament extrusion, discharging the sporoplasm, has also been offered(13), based on experiments with 2xtrusion: after the spore has been activated, the polaro->last quickly imbibes water from the environment. This :awes a considerable intrasporal pressure, forcing the holow filament to evaginate-the fluid of the posterior vacu-3le plays an important role-thru the anterior end of the ,hell, while the sporoplasm is being pushed thru the whole length of the filament out of the spore. Some of the stages If this process need further clarification, and additional -esearch on the structure of the ripe spore, especially on :he filament's fine structure, seems necessary.With respect to electron-microscopic studies of the de-:elopmen t cycles of microsporidians which might reveal .he origin of the highly specialized structures of the spore, LS well as make possible a comparison with development n groups such as those comprising the myxosporidians or iaplosporidians, only few studies have appeared to date. The observations of de Puytorac( 16) on Mrazekia lumbri-7uli and of VBvra(22) on the genera Thelohank and 141 of the filament, and a middle, electron-transparent layer. The structure of the filament is discussed in relation to its function and with regard to the findings of other authors.The polmoplast is a laminated structure, originating possibly by transformation of endoplasmic reticulum; the polar cap forms its apical part. The cap is also lamellar; its substance r...

Ameson metacarcini sp. nov. (Microsporidia) infecting the muscles of Dungeness crabs Metacarcinus magister from British Columbia, Canada

“…This analysis was performed using the Tamura-Nei model of evolution within MEGA 6. Numbers at nodes represent bootstrap support values for each clade (1981) suggested that they may aid dispersal of the released spore stage in aquatic environments and Lom & Corliss (1967) conjectured that they may be involved in transporting metabolites from the host to the parasite. Phylogenetic data confirmed our ultrastructural observations of an affiliation of A. metacarcini within the genus Ameson as it placed with 100% support within a clade containing A. michaelis, A. pulvis, and N. canceri.…”

The microsporidian polar tube: A highly specialised invasion organelle

“…However, staining of the polar filament core, its outer sheath and its originating vacuoles was also seen with nucleoside disphosphatase (NDPase), which is a marker for endoplasmic reticulum as well as cis-Golgi membrane (Takvorian and Cali, 1996). The polaroplast has also been reported to be derived from the Golgi Jensen and Wellings, 1972) and the endoplasmic reticulum (Lom and Corliss, 1967;Weidner, 1970).…”

“…Moreover, a different pattern of layers has been observed before, during and after extrusion (Lom, 1972;Vavra, 1976;Chioralia et al, 1998;Cali et al, 2002). An electron dense particulate material fills the centre of the filament (Kudo and Daniels, 1963;Lom and Vavra, 1963;Vavra, 1976) and it undergoes changes during the eversion process (Lom and Corliss, 1967;Cali et al, 2002). Weidner proposed that this material is unpolymerised polar tube protein (Weidner, 1972(Weidner, , 1976.…”

Occurrence of microsporidians Glugea hertwigi and Pleistophora ladogensis, in smelt Osmerus eperlanus from two German rivers, North Sea coast

“…In our study, only microspores were observed in the fresh mounts and in several ultrathin sections. Some other Pleistophora species do not produce 2 types of spores, for example P. hyphessobryconis, P. hippoglossoideos, and P. senegalensis (Lom & Corliss 1967, Morrison et al 1984, Faye et al 1990, suggesting that this feature may not be relevant for the diagnosis of the genus Pleistophora (Faye et al 1990). As in our study, Voronin (1981) found that prevalence of P. ladogensis in smelt from 11 to 22 cm long was 5 to 8%, in contrast to 32 to 50% in burbot L. lota, suggesting that smelt is a secondary host of P. ladogensis, and its typical host is burbot.…”