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Intracellular parasites of the genus Glugea Thélohan, 1891 (Microsporidia) comprise about 34 putative species capable of causing high morbidity and mortality in freshwater and marine teleost fishes. In this study, we report on the first mass mortality event associated with Glugea sp. infecting free-ranging round sardinella Sardinella aurita in the southern Tyrrhenian Sea (Italy). Here, we describe the ultrastructure of mature spores of this microsporidian and characterize it molecularly, as well as report its phylogenetic position. Most of the affected fish showed an irregular swelling of its abdomen. At necropsy, a variable number of xenomas, spherical to ellipsoidal in shape, were found in the peritoneal cavity strongly attached to the viscera of all fish. Histological analysis revealed varying severity of chronic inflammation along with occasional necrosis in visceral organs associated with multiple xenoma proliferation. These pathological findings were considered the main cause of this mass mortality event. Morphologically, the present material was closely related to G. sardinellesis and G. thunni. The phylogenetically closest taxa to the newly SSU rDNA sequence were G. thunni and an erroneusly identified  G. plecoglossi, which were very closely related to each other, also suggesting that all these sequences might belong to the same species., (© 2024 John Wiley & Sons Ltd.)

A new microsporidian infecting the connective tissue of the coelomic cavity of the blacktail comber Serranus atricauda, in the Madeira Archipelago (Portugal), is described on the basis of morphological, ultrastructural, and molecular features. The microsporidian formed large whitish xenomas adhering to the peritoneal visceral organs of the host. Each xenoma consisted of a single hypertrophic cell, in the cytoplasm of which mature spores proliferated within parasitophorous vacuoles surrounded by numerous collagen fibers. Mature spores were ellipsoidal and uninucleated, measuring an average of 6.5 ± 0.5 μm in length and 3.4 ± 0.6 μm in width. The anchoring disk of the polar filament was subterminal, laterally shifted from the anterior pole of the spore. The isofilar polar filament coiled in 18-19 turns, forming two rows that surrounded the posterior vacuole. The latter occupied about one third of the spore length. The polaroplast surrounding the apical and uncoiled portion of the polar filament displayed two distinct regions: a lamellar region and an electron-dense globule. Molecular analysis of the rRNA genes, including the internal transcribed spacer region, and phylogenetic analysis using maximum likelihood and neighbor joining demonstrated that this microsporidian parasite clustered with some Glugea species. Based on the differences found both at the morphological and molecular levels, to other members of the genus Glugea, the microsporidian infecting the blacktail comber is considered a new species, thus named Glugea serranus n. sp.

A new microsporidian species, Glugea arabica n. sp., is reported infecting the intestinal wall of the marine teleost Epinephelus polyphekadion (=microdon) collected from the Red Sea coast off Saudi Arabia, and described on the basis of microscopic and molecular procedures. Spherical blackish xenomas formed parasitophorous vacuoles completely packed with several parasitic developmental stages, including spores. The nuclei were monokaryotic in all developmental stages. Spores were ellipsoidal to pyriform and measured 6.3 ± 0.3 (5.9-6.6) μm in length and 3.3 ± 0.4 (2.9-3.7) μm in width. A lamellar polaroplast surrounded the uncoiled portion of the polar filament, which extended into the spore's posterior pole and formed 27-29 coils organized in three or four rows. The posterior vacuole, located at the spore's posterior pole, appeared surrounded by the polar filament coils and displayed an irregular matrix composed of light material, in which was located the posterosome. Molecular analysis of the rRNA genes, including the ITS region, was performed using maximum parsimony, neighbor-joining and maximum likelihood methodologies. The ultrastructural features observed, in combination with the molecular data analysed, suggests the parasite to be a new species of the genus Glugea., (Copyright © 2015 Elsevier GmbH. All rights reserved.)

During a survey of the microsporean fauna of the two-spot red snapper Lutjanus bohar Forsskål, 1775, from the Red Sea off Jizan (Saudi Arabia), a species of Glugea Thélohan, 1891 was found that did not conform to any known species. The species is characterized by the presence of spherical xenomas (ca. 2-5 mm in diameter) in the host body cavity. Examination of the lifecycle stages and mature spores using light and transmission electron microscopy also revealed morphological characteristics typical of species of the genus Glugea. Spores were elongated-ovoid with a posterior vacuole surrounded by the polar filament coils. Mature spores were 4.5 (4.0-4.8) µm long and 2.5 (2.0-2.5) µm wide. The polar filament was isofilar with 28 to 30 coils, although in most cases 29 coils, organized in 3 rows. Phylogenetic study based on the partial sequence of the small subunit (SSU) rRNA gene clustered the new microsporidia within the clade grouping species of the genus Glugea. The comprehensive analysis of the parasite's ultrastructural characteristics, together with molecular data for the SSU rDNA gene, suggests that this parasite is a new species of the genus Glugea, for which the name Glugea jazanensis sp. nov. is proposed.

The microsporidium Glugea gasterostei from the three-spined stickleback Gasterosteus aculeatus was described as an independent species basing upon morphological and ecological traits of the parasite (Voronin, 1974), further supported by ultrastructural characters of its spores (Voronin, 1983). During the revision of microsporidia of the genus Glugea (Canning, Lom, 1986; Lom, 2002), the validity of this species was doubted and it was synonymized with G. anomala. Nevertheless, the molecular phylogenetic analysis performed in the present study showed the unique molecular haplotype of small subunit rRNA gene of G. gasterostei (Genbank accession number KM977990) and its close relatedness to G. anomala, G. atherinae and G. hertwigi (sequence similarity of 99.7 %). One of typical characters of G. gasterostei, as opposed to G. anomala, is the formation of xenomas on inner tissues and not on the surface of infected fishes. This feature is retained even after the infection of different host species. Taken together, these data confirm the validity of G. gasterostei as a separate species among closely related taxa that had diverged comparatively recently.

A new microsporidian species is described from farmed red sea bream Pagrus major (Temminck & Schlegel) (Teleostei: Sparidae). Large numbers of spherical whitish xenomas were observed throughout the visceral organs of the host. Histological examination showed that the microsporidia caused several xenomas that were embedded in the intestinal muscularis externa or submucosa. Light and transmission electron microscopy examination of the spores also revealed morphological features typical of species of Glugea Thélohan, 1891. This microsporidian parasite has two different types of mature spores: microspores and macrospores. The spores are elongate-ovoid, with a large posterior vacuole. The polaroplast is bi-partite, with anterior and posterior parts comprising densely packed lamellae and loose membranes, respectively, and occupies approximately the anterior half of the spore. The polar filament is anisofilar, with 12-13 coils in a single layer almost touching the posterior spore wall. Comparison of the small subunit rDNA sequences revealed 92.7-98.1% identity with the sequences available from other Glugea spp. from piscine hosts. Phylogenetic analysis demonstrated that the microsporidian species studied clustered within the Glugea clade with strong support. Based on the differences in the morphological characteristics and molecular data, the microsporidian infecting P. major is considered to represent a species new to science, Glugea pagri n. sp.

Infection of rainbow smelt Osmerus mordax with the microsporidian Glugea hertwigi was diagnosed for the first time in Prince Edward Island, Canada. The prevalence of infection was 24%, 45 infected out of 187 examined fish captured in February and March 2009. Both large and small xenomas of G. hertwigi observed within the submucosa of the gastrointestinal tract and along the mesentery of the host contained only mature spores. Advanced and degraded xenomas associated with host reaction were described using light and transmission electron microscopy. The first rDNA sequence of G. hertwigi prepared in the present study completed the set of sequences of Glugea spp. available for comparison. The high level of rDNA sequence identity between Glugea spp. suggests that these may be variants of a single species.