Ultrastructure and molecular phylogeny of Pleistophora hyphessobryconis (Microsporidia) infecting hybrid jundiara (Leiarius marmoratus × Pseudoplatystoma reticulatum) in a Brazilian aquaculture facility.

A microsporidian infecting the skeletal muscle of hybrid jundiara (Leiarius marmoratus × Pseudoplatystoma reticulatum) in a commercial aquaculture facility in Brazil is described. Affected fish exhibited massive infections in the skeletal muscle that were characterized by large opaque foci throughout the affected fillets. Histologically, skeletal muscle was replaced by inflammatory cells and masses of microsporidial developmental stages. Generally pyriform spores had a wrinkled bi-layer spore wall and measured 4·0 × 6·0 µm. Multinucleate meronts surrounded by a simple plasma membrane were observed. The polar filament had an external membrane and a central electron dense mass. The development of sporoblasts within a sporophorous vesicle appeared synchronized. Ultrastructural observations and molecular analysis of 16S rDNA sequences revealed that the microsporidian was Pleistophora hyphessobryconis. This study is the first report of a P. hyphessobryconis infection in a non-ornamental fish.

Ultrastructure and molecular phylogenetics of a new isolate of Pleistophora pagri sp. nov. (Microsporidia, Pleistophoridae) from Pagrus pagrus in Egypt.

The spore morphology and molecular systematic of a new microsporidian which was isolated from the common sea bream Pagrus pagrus (F: Sparidae Linnaeus, 1758) from the Red Sea, Egypt have been studied. Fifty-six out of 300 (18.7%) of this fish were infected with microsporidian parasites. The infection was appeared as whitish, ellipsoid, round, or elongated nodules embedded in the epithelial lining of the peritoneum and also in the intestinal epithelium. Light microscopic study revealed that nodules were encapsulated by a fibrous layer encircling numerous mature spores measuring 1.7 ± 0.6 (1.5-2.7 µm) × 1.5 ± 0.3 µm (1.2-1.8 µm) in size. Ultrastructure of spores was characteristic for the genus Pleistophora: dimorphic, uninucleate spores (each spore possesses three to five polar filament coils) and a posterior vacuole. Also, the early recognizable stages of the parasite within nodules include uninucleated, binucleated, and multinucleated meronts followed by detachment of the plasmalemma of the sporont producing sporoblasts which mature to spores that consist of a spore coat and spore contents. Also, we analyzed the small subunit ribosomal gene (SSUrDNA) using PCR and sequencing specimens from the marine populations of P. pagrus fish from the Red Sea. From blast searches, sequence analysis, and phylogenetic analysis, we did not find corresponding GenBank entries to our species. Comparison of the nucleotide sequences showed that the sequence of our microsporidium was most similar to five Pleistophora species with degrees of identity (>91.5%). It was most similar (97.8% identity) to that of Pleistophora hyphessobryconis (account no. GU126672) differing in 19 nucleotide positions and with lower divergence value, Pleistophora ovariae (96.2% identity, account no. AJ252955), Pleistophora hippoglossoideos (91.9% identity, account no. AJ252953), Pleistophora mulleri (91.9% identity, account no. EF119339), and Pleistophora typicalis (91.9% identity, account no. AJ252956). So, they likely represent new species named Pleistophora pagri sp. n. with accession number JF797622 and a GC content of 53%.

Morphological and molecular biological characterization of Pleistophora aegyptiaca sp. nov. infecting the Red Sea fish Saurida tumbil.

One hundred three out of 225 (45.8%) of the Red Sea fish Saurida tumbil were infected with microsporidian parasites. The infection was recorded as tumor-like masses (whitish macroscopic cysts) or xenomas often up to 2 cm in diameter and embedded in the peritoneal cavity. Generally, the infection was increased during winter 63.8% (86 out of 135) and fall to 18.9% (17 out of 90) in summer. Light microscopic study revealed that xenomas were encapsulated by a fibrous layer encircling numerous sporophorous vesicles filled with mature spores measuring 1.7 ± 0.6 (1.5-2.7 µm) × 1.5 ± 0.3 µm (1.2-1.8 µm) in size. Ultrastructural microscopic study showed the presence of smooth membranes of the sarcoplasmic reticulum forming a thick, amorphous coat surrounding various developmental stages of the parasite. The various recognizable stages of the parasite were uninuclear, binucleated, and multinucleated meronts followed by detachment of the plasmalemma of the sporont from the sporophorous vesicle producing sporoblasts. Mature spores consist of a spore coat and spore contents. The spore contents consist of the uninucleated sporoplasm and a posterior vacuole located at the posterior end. The polar tube consists of a straight shaft and a coiled region (26-32 coils) arranged in many rows along the inside periphery of the spore. The polaroplast consisted of an anterior region of closely and loosely packed membranes. Molecular analysis based on the small subunit rDNA gene was performed to determine the phylogenetic position of the present species. The percentage identity between this species and a range of other microsporidia predominantly from aquatic hosts demonstrated a high degree of similarity (>92%) with eight Pleistophora species. Comparison of the nucleotide sequences and divergence showed that the sequence of the present microsporidium was most similar to that of Pleistophora anguillarum (99.8% identity) differing in 13 nucleotide positions. So, the present species was recorded and phylogenetically positioned as a new species of Pleistophora.

Distribution and host range of the microsporidian Pleistophora mulleri.

Microsporidia of the genus Pleistophora are important parasites of fish and crustacea. Pleistophora mulleri has been described previously as a parasite of the gammarid amphipod crustacean Gammarus duebeni celticus in Irish freshwater habitats. Through a survey of European G. duebeni populations, P. mulleri was found to be widely distributed in the western British Isles (Wales, Scotland, and the Isle of Man), and populations of the subspecies Gammarus duebeni duebeni as well as G. d. celticus were infected. Pleistophora infections were also detected in G. d. duebeni sampled from the Bay of Gdansk on Poland's Baltic coast, indicating a wide distribution of Pleistophora in European G. duebeni. Sequencing and phylogenetic analysis of the 16S rRNA, 18S rRNA, and Rpb1 genes of P. mulleri suggest that this species may be synonymous with P. typicalis, a parasite of fish. These findings suggest that amphipod crustaceans may act as intermediate or reservoir hosts for microsporidian parasites of fish.

Resolution of a taxonomic conundrum: an ultrastructural and molecular description of the life cycle of Pleistophora mulleri (Pfeiffer 1895; Georgevitch 1929).

The classification of a microsporidian parasite observed in the abdominal muscles of amphipod hosts has been repeatedly revised but still remains inconclusive. This parasite has variable spore numbers within a sporophorous vesicle and has been assigned to the genera Glugea, Pleistophora, Stempellia, and Thelohania. We used electron microscopy and molecular evidence to resolve the previous taxonomic confusion and confirm its identification as Pleistophora mulleri. The life cycle of P. mulleri is described from the freshwater amphipod host Gammarus duebeni celticus. Infection appeared as white tubular masses within the abdominal muscle of the host. Light and transmission electron microscope examination revealed the presence of an active microsporidian infection that was diffuse within the muscle block with no evidence of xenoma formation. Paucinucleate merogonial plasmodia were surrounded by an amorphous coat immediately external to the plasmalemma. The amorphous coat developed into a merontogenetic sporophorous vesicle that was present throughout sporulation. Sporogony was polysporous resulting in uninucleate spores, with a bipartite polaroplast, an anisofilar polar filament and a large posterior vacuole. SSU rDNA analysis supported the ultrastructural evidence clearly placing this parasite within the genus Pleistophora. This paper indicates that Pleistophora species are not restricted to vertebrate hosts.