Fine structure of the cyst and some sporulation stages of Ichthyosporidium (Microsporida)

Ichthyosporidium weissii n. sp. (Microsporidia) infecting the arrow goby (Clevelandia ios)

Gonadal infections by a novel microsporidium were discovered in 34% (13/38) of arrow gobies, Clevelandia ios, sampled over a 3-yr period from Morro Bay Marina in Morro Bay, California. Gonadal tumors had been reported in arrow gobies from this geographic area. The infected gonads, found primarily in females, typically appeared grossly as large, white-gray firm and lobulated masses. Histological examination revealed large, multilobate xenomas within the ovaries and no evidence of neoplasia. Typical of the genus Ichthyosporidium, the large xenomas were filled with developmental stages and pleomorphic spores. Wet mount preparations showed two general spore types: microspores with mean length of 6.2 (7.0-4.9, SD = 0.6, N = 20) μm and mean width of 4.3 (5.3-2.9, SD = 0.8) μm; and less numerous macrospores with mean length of 8.5 (10.1-7.1, SD = 1.0, N = 10) μm and mean width of 5.5 (6.2-4.8, SD = 0.5) μm. Transmission electron microscopy demonstrated stages consistent with the genus and 35-50 turns of the polar filament. Small subunit rDNA gene sequence analysis revealed that the parasite from arrow gobies was most closely related to, but distinct from Ichthyosporidium sp. based on sequences available in GenBank. We conclude that this microsporidium represents a new species of Ichthyosporidium, the first species of this genus described from a member of the family Gobiidae and from the Pacific Ocean.

A new microsporidian parasite, Potaspora morhaphis n. gen., n. sp. (Microsporidia) infecting the Teleostean fish, Potamorhaphis guianensis from the River Amazon. Morphological, ultrastructural and molecular characterization

A fish-infecting Microsporidia Potaspora morhaphis n. gen., n. sp. found adherent to the wall of the coelomic cavity of the freshwater fish, Potamorhaphis guianensis, from lower Amazon River is described, based on light microscope and ultrastructural characteristics. This microsporidian forms whitish xenomas distinguished by the numerous filiform and anastomosed microvilli. The xenoma was completely filled by several developmental stages. In all of these stages, the nuclei are monokaryotic and develop in direct contact with host cell cytoplasm. The merogonial plasmodium divides by binary fission and the disporoblastic pyriform spores of sporont origin measure 2·8±0·3×1·5±0·2 μm. In mature spores the polar filament was arranged into 9–10 coils in 2 layers. The polaroplast had 2 distinct regions around the manubrium and an electron-dense globule was observed. The small subunit, intergenic space and partial large subunit rRNA gene were sequenced and maximum parsimony analysis placed the microsporidian described here in the clade that includes the genera Kabatana, Microgemma, Spraguea and Tetramicra. The ultrastructural morphology of the xenoma, and the developmental stages including the spores of this microsporidian parasite, as well as the phylogenetic analysis, suggest the erection of a new genus and species.

Amazonspora hassar n. gen. and n. sp. (phylum Microsporidia, fam. Glugeidae), a parasite of the Amazonian teleost Hassar orestis (fam. Doradidae)

We describe the microsporidian Amazonspora hassar n. gen., n. sp. from the gill xenomas of the teleost Hassar orestis (Doradidae) collected in the estuarine region of the Amazon River. The parasite appeared as a small whitish xenoma located in the gill filaments near the blood vessels. Each xenoma consisted of a single hypertrophic host cell (HHC) in the cytoplasm of which the microsporidian developed and proliferated. The xenoma wall was composed of up to approximately 22 juxtaposed crossed layers of collagen fibers. The plasmalemma of the HHC presented numerous anastomosed, microvilli-like structures projecting outward through the 1-3 first internal layers of the collagen fibrils. The parasite was in direct contact with host cell cytoplasm in all stages of the cycle (merogony and sporogony). Sporogony appears to divide by plasmotomy, giving rise to 4 uninucleate sporoblasts, which develop into uninucleate spores. The ellipsoidal spores measured 2.69 +/- 0.45 x 1.78 +/- 0.18 microm, and the wall measured approximately 75 nm. The anchoring disk of the polar filament was subterminal, being shifted laterally from the anterior pole. The polar filament was arranged into 7-8 coils in a single layer in the posterior half of the spore, surrounding the posterior vacuole. The polaroplast surrounded the uncoiled portion of the polar filament, and it was exclusively lamellar. The spores and different life-cycle stages were intermingled within the cytoplasm of the HHC, surrounding the central hypertrophic deeply branched nucleus. The ultrastructural morphology of this microsporidian parasite suggests the erection of a new genus and species.

Fish microsporidia: fine structural diversity and phylogeny

Structural diversity of fish microsporidian life cycle stages and of the host-parasite interface is reviewed. In the infected cell of the fish host, microsporidia may either cause serious degradation of the cytoplasm and demise of the cell, or they may elicit host cell hypertrophy, producing a parasite-hypertrophic host cell complex, the xenoma. The structure of the xenoma and of its cell wall may differ according to the genus of the parasite, and seems to express properties of the parasite rather than those of the host. In merogony, the parasite cell surface interacts with the host cell in diverse ways, the most conspicuous being the production of thick envelopes of different types. Sporogony stages reveal different types of walls or membranes encasing the sporoblasts and later the spores and these envelopes may be of host or parasite origin. Nucleospora differs from all other fish microsporidia by its unique process of sporogony. Except for the formation of conspicuous xenomas, there are no essentially different structures in fish-infecting microsporidia compared with microsporidia from other hosts. Although the structures associated with the development of fish microsporidia cannot be attributed importance in tracing the phylogeny, they are relevant for practical determination and assessing the relation to the host. The possibility of the existence of an intermediate host is discussed. Higher-level classification of Microsporidia is briefly discussed and structure and evolutionary rates in microsporidian rDNA are reviewed. Discussion of rDNA molecular phylogeny of fish-infecting microsporidia is followed by classification of these parasites. Most form a rather cohesive clade. Outside this clade is the genus Nucleospora, separated at least at the level of Order. Within the main clade, however, there are six species infecting hosts other than fish. Based on data available for analysis, a tentative classification of fish-infecting microsporidia into five groups is proposed. Morphologically defined groups represent families, others are referred to as clades. Group 1, represented by family Pleistophoridae, includes Pleistophora, Ovipleistophora and Heterosporis; Vavraia and Trachipleistophora infect non-fish hosts. Group 2, represented by family Glugeidae, is restricted to genus Glugea and Tuzetia weidneri from crustaceans. Group 3 comprises three clades: Loma and a hyperparasitic microsporidian from a myxosporean; Ichthyosporidium and Pseudoloma clade and the Loma acerinae clade. For the latter species a new genus has to be established. Group 4 contains two families, Spragueidae with the genus Spraguea and Tetramicridae with genera Microgemma and Tetramicra, and the Kabatana and Microsporidium seriolae clade. Group 5 is represented by the family Enterocytozoonidae with the genus Nucleospora and mammal-infecting genus Enterocytozoon.

Ultrastructural qualitative and quantitative data on the sporogenesis of the protozoan Abelspora portucalensis (Microspora, Abelsporidae): a different approach to the study of microsporidia

The sporogenesis of the microsporidium Abelspora portucalensis was studied with electron microscopy. In qualitative terms, new aspects of the cytoplasmic ultrastructure of the schizont, sporont, and sporoblast are described: the presence of microtubules, of aggregates of small opaque vesicles, and of dispersed larger vesicles with clear matrix. The hypothesis that the opaque vesicles may represent the Golgi apparatus and the clear vesicles may correspond to the smooth endoplasmic reticulum is discussed. The use of standard stereological and statistical techniques gives us a new perspective on the development of this microsporidium. The most relevant quantitative data display that the amount of rough endoplasmic reticulum (either in relative or absolute terms) presents significant differences among the three stages, with the sporont showing the highest values; that the absolute (but not the relative) volume of the large vesicles significantly changes during sporogenesis with the highest values presented by the sporont; that the surface-to-volume ratio of the schizont and sporont cells is similar and significantly greater than that of the sporoblast cell; that the surface density of the nucleus in relation to soma remains constant in the three stages (on the contrary, the surface-to-volume ratio of the nucleus increases and its volumetric density diminishes); and finally, that the nucleolus decreases its relative and absolute volumes. The functional significance of these results is analyzed and the application of similar methodology in quantifying the effects of drugs upon microsporidia is suggested.

Observations on Ichthyosporidium giganteum (Microsporida) with particular reference to the host-parasite relations during merogony

Connective tissue cells, particularly fibroblasts, of the fish Leiostomus xanthurus Lacépède respond to the invading microsporidian parasite Ichthyosporidium sp. [assumed to be identical with Ichthyosporidium giganteum (Thélohan)] by proliferating themselves, coalescing into a syncytium, synthesizing copious amounts of cytoplasm around the parasites, and walling off the parasitized islands of cytoplasm with fibrous capsules. The resulting cysts are xenoparasitic complexes of the syncytial xenoma type, clearly different from the cell hypertrophy tumor (xenoma sensu Weissenberg) exemplified by the Glugea cyst. These findings involve a new concept of the structure and host-parasite relations of Ichthyosporidium. Formerly, the parasitized masses of cytoplasm were interpreted as extracellular plasmodial stages of the parasite (stages uncharacteristic of the microsporidia), while the parasites themselves were interpreted as nuclei of the "plasmodia." Actually, the parasite undergoes merogony in parasitophorous vacuoles which coalesce before sporogony begins. The nuclei of the mermonts are very small chromatin granules, becoming transformed into large basophilic diplokarya of the sporonts. Sporulation is diplokaryotic throughout, the diplokarya becoming reduced in size through 2 steps during sporogony.

[Ormiersia carcini gen. n., sp. n., microsporidian of the Mediterranean crab, Carcinus mediterraneus Czerniavsky, 1844: developmental cycle and ultrastructural study]

A microsporidan parasite, Ormieresia carcini gen. n., sp. n., was found in the crab, Carcinus mediterraneus Czerniavsky. Its development and fine structure are the subject are the subject of the present study. The life cycle begins with a schizont surrounded by a unit membrane and containing a diplokaryon. The entire process of sporogony takes place in the host musculature. The sporogonic stages are enclosed in the pansporoblastic membrane. In each pansporoblast, sporogony gives rise to 8 sporoblasts; the octonucleate sporogonial plasmodium is lacking. In the course of schizogonic and sporogonic divisions, each kinetic center consists of 2 plaques, one located within and the other outside the nuclear envelope. The dividing sporonts and sporoblasts sevrets "metabolic" substances (granules, tubules) which are depostied in the pansporoblast. The uninucleate spore is long and cylindrical, measuring 19.1 X 2.4 micronm. A rectilinear manubrium traverses the spore. Its posterior end attenuates abruptly into a polar filament with 4 or 5 coils; its anterior end is attached to the polar cap, which is compressed by a double polar ring. The anterior part of the manubrium is surrounded by a polaroplast consisting of a "spongy" (vesicular) and a lamellar zone.

Some ultrastructural and functional aspects of the golgi àpparatus of Thelohania sp. (Microsporida) in the shrimp Pandalus jordani Rathbun

Electron microscope observations on Thelohania sp. in the shrimp Pandalus jordani support the view that the Golgi complex in Microsporida is a "classical" one, composed of vesicular, vacuolar, and cisternal components. During development of the sporoblast, a portion of the Golgi complex is seen as an electron-dense reticulum enmeshing the core of the polar filament. Associated with the reticulum are electron-dense bodies. The reticulum and "dense bodies," reported in several previous publications, have not been well understood and have been given a variety of names. The evidence favors the view that these structures have secretory activity in which the reticulum concentrates or synthesized material, some of which takes the form of membrane-bounded granules. It is suggested that the most appropriate name for the reticulum is "reticulum golgien," and the the correct name for the "dense bodies" is the standard cytologic term, "secretion granules." The secretion granules apparently remain in the posterior part of the spore, and may be stored there for some as yet undetermined use.