A new species of myxosporean (Sphaeromyxidae), a parasite of lined seahorses, Hippocampus erectus, from the Gulf of Mexico

Characterization and expression patterns of lysozymes reveal potential immune functions during male pregnancy of seahorse

Seahorses are one of the most amazing ovoviviparous fishes in the ocean because males, and not females, have evolved a brood pouch for incubating embryos. During male pregnancy, paternal seahorses need to develop effective immune protection for embryos in the brood pouch from potential infection by pathogens. Lysozymes (Lyz) are a group of antibacterial enzymes of the innate immune system that play an important role in resisting pathogen invasion. However, the immune function of lysozymes in the brood pouch of the pregnancy-lined seahorse (Hippocampus erectus) remains unknown. In this study, we found three different lysozymes in the lined seahorse: HeLyzC, HeLyzG1, and HeLyzG2. Synteny analysis revealed that HeLyzG1 and HeLyzG2 were generated by species-specific expansion rather than tandem duplication. Tissue expression patterns showed that the highest mRNA expression levels of the three lysozymes occurred in the brood pouches. Immunostimulation-induced expression analysis showed that all three HeLyzs in the brood pouches up-regulated their mRNA expression levels after Vibrio parahaemolyticus infection, but only the HeLyzG2 was upregulated after Poly(I:C) injection. Similarly, except for HeLyzC, upregulated expressions of HeLyzG1 and HeLyzG2 were found quickly in brood pouches injected with LPS. The upregulated levels of HeLyzC and HeLyzG2 in brood pouches during pregnancy were significantly higher than those in non-pregnancy, implying that seahorse lysozymes might function in the immune defense in brood pouches during pregnancy. In addition, the expression levels of HeLyzs were low in embryos in the brood pouch but significantly increased in neonates. This implies that embryos in the brood pouch might not necessarily express more lysozymes by themselves due to paternal immune protection. In conclusion, our study demonstrated that HeLyzs play an important role in immune protection during male seahorse gestation, and the synergistic effect of multiple HeLyzs may contribute to improved neonatal survival.

Sphaeromyxa azevedoi n. sp. (Myxozoa: Sphaeromyxidae) infecting the gall bladder of Gobioides grahamae (Perciformes: Gobiidae) in the Amazon region

Sphaeromyxa azevedoi n. sp. is described from the gall bladder of the goby Gobioides grahamae (Gobiidae) captured on the Paracauari River in Salvaterra, on Marajó Island, northern Brazil. A total of 50 G. grahamae specimens were analysed, and 15 (30%) were parasitised by the plasmodia and myxospore of Sphaeromyxa azevedoi n. sp. Large plasmodia were observed floating in the bile. These plasmodia were flat, rounded, oval or elongated, and of varying sizes. The mature myxospores, found singly or in pairs, were 27.1 ± 2.7 (20.5-30.1) μm Length and 3.8 ± 0.2 (3.5-4.4) μm Width in the valvular view. The myxospore has two polar capsules of equal size, 8.1 ± 0.6 (7.4-9.4) μm in length and 2.9 ± 0.2 (2.3-3.3) μm in width. A polar tubule was observed in each capsule, arranged perpendicularly to the principal axis, with three or four coils. The histological analysis showed that the plasmodia and myxospore are located in the lumen of the gall bladder, arranged in pairs, and the epithelium of the gall bladder presented multifocal necrosis. The SSU rDNA of Sphaeromyxa azevedoi n. sp. clusters in the 'balbianii' group of the Sphaeromyxa clade. The morphological characteristics and molecular phylogeny of Sphaeromyxa azevedoi n. sp. support its classification as a new species of the genus Sphaeromyxa, which represents an important advancement in the understanding of the diversity of the myxozoan parasite fauna of Brazilian fishes, especially considering that the new species may be detrimental to the host, a commercially important Brazilian fish species.

The first report of two Sphaeromyxa species (Myxozoa: Bivalvulida) from the South China Sea: Sphaeromyxa scorpaena n. sp. from long-fingered scorpionfish (Scorpaenodes albaiensis) and Sphaeromyxa theraponi from tiger perch (Terapon jarbua)

Two myxosporean species of the genus Sphaeromyxa were isolated from the gallbladders of marine fish in the South China Sea. Sphaeromyxa scorpaena n. sp. was collected from Scorpaenodes albaiensis Evermann and Seale, 1907. The mature myxospores were arcuate-shaped with tapered to pointed ends, and a length of 14.1 ± 0.7 (13.8-15.1) μm and a width of 5.2 ± 0.3 (4.9-5.8) μm. The polar capsules (PCs) were pyriform with a length of 3.2 ± 0.2 (3.1-3.5) μm and a width of 1.6 ± 0.1 (1.4-1.8) μm, and containing ribbon-like polar filaments irregularly folded 1.5-2.5 turns. Molecular characteristics and phylogenetic analysis based on 18S rDNA as well as morphological comparison confirmed that S. scorpaena n. sp. was a previously undescribed species. Sphaeromyxa theraponi, isolated from Terapon jarbua Forsskål, 1775, was reported for the first time from the South China Sea. The mature myxospores were slightly arched, tapering to bluntly rounded ends, with a length of 17.3 ± 0.9 (15.5-19.4) μm and a width of 4.8 ± 0.3 (4.1-5.3) μm. A sporoplasm was situated in the space between PCs in the myxospore. The PCs were pyriform, which contained ribbon-like polar filaments irregularly folded by 2-3 turns, with a length of 7.0 ± 0.5 (5.8-8.1) μm and a width of 2.6 ± 0.2 (2.2-3.0) μm. Our morphological and phylogenetic analyses suggest that the pointed ends of S. scorpaena n. sp. might be a secondarily acquired characteristic rather than an ancestral trait.

Taxonomy on three novel species of Sphaeromyxa Thélohan 1892 (Myxozoa, Bivalvulida, Sphaeromyxidae) with insight into the evolution of the genus

Three new myxosporeans of the genus Sphaeromyxa Thélohan 1892 were discovered from the coastal waters off Xiamen in the East China Sea and characterized based on morphological and SSU rDNA data. Sphaeromyxa photopectoralis sp. n. was described from Photopectoralis bindus, and Sphaeromyxa sebastisca sp. n. was described infecting both Sebastiscus marmoratus (type-host) and Scorpaenopsis cirrosa. These two species are morphologically consistent with the "balbianii" group, possessing straight myxospores and truncated ends, but are distinct from one another genetically and by myxospore dimensions. A third myxosporean infecting Siganus fuscescens was described as Sphaeromyxa xiamenensis sp. n., and this species is morphologically consistent with the "incurvata" group, bearing arcuate myxospores with rounded ends. The molecular phylogeny and estimated rRNA secondary structure suggest that marine sphaeromyxids are probably derived from freshwater myxidiids, and "incurvata" and "balbianii" groups might each represent independent evolutionary lineages. The present study also shows that S. limocapitis phylogenetically nested in "incurvata" group.

Sphaeromyxa artedielli sp. n. (Myxozoa: Sphaeromyxidae), a parasite of sculpins (Cottidae) in northern Norway

Sphaeromyxa artedielli sp. n. is described from the gall bladder of the Atlantic hookear sculpin Artediellus atlanticus Jordan et Evermann (Cottidae; type host) from northern Norway. The parasite was also found to infect Triglops murrayi Günther (Cottidae). Spores are produced in disporic pansporoblasts in large flat plasmodia. Spores are straight and fusiform with truncated ends, and measure 16.5-18.7 microm x 4.9-6.2 microm. Valves are thick, striated and suture line is straight. Two equal ovoid polar capsules measure 4.2-6.8 microm x 2.9-4.4 microm and contain irregularly folded polar filaments. Distinctive features include spore shape and size, spore length/width relationship, striated valves, equal polar capsules and a short intercapsular distance. Sphaeromyxa bonaerensis Timi et Sardella, 1998, Sphaeromyxa cannolii Sears, Anderson et Greiner, 2011, and Sphaeromyxa sevastopoli Naidenova, 1970 produce straight spores with truncated ends that are of similar length as those of the new species. Sphaeromyxa cannolii differs in showing smooth spores with unequal polar capsules. The new species differs from S. bonaerensis and S. sevastopoli in significantly wider spores and polar capsules. Sphaeromyxa balbianii Thélohan, 1892, a species originally described with significantly smaller spores than S. artedielli sp. n., has previously been recorded from T. murrayi. We show that S. artedielli sp. n. differs from S. balbianii from the type host Gaidropsarus vulgaris (Cloquet) by its SSU rDNA sequence, and suggest that Atlantic records of Sphaeromyxa spp. from T. murrayi represent S. artedielli sp. n. The closest relative to S. artedielli sp. n. according to the SSU rDNA sequences, S. longa Dunkerly, 1921, differs clearly by spore size and shape. In the SSU rDNA-based phylogenetic analyses, S. artedielli sp. n. groups with other Sphaeromyxa spp. with straight spores and truncated ends in a clade that represents a sister-group to Sphaeromyxa spp. with arcuate spores and rounded ends. Our results indicate that an SSU rDNA pseudogene is present in S. balbianii.

Sphaeromyxids form part of a diverse group of myxosporeans infecting the hepatic biliary systems of a wide range of host organisms

Background

Approximately 40 species of Sphaeromyxa have been described, all of which are coelozoic parasites from gall bladders of marine fish. They are unique amongst the myxosporeans as they have polar filaments that are flat and folded instead of being tubular and spirally wound. This unusual feature was used as a subordinal character to erect the suborder Sphaeromyxina, which contains one family, the Sphaeromyxidae, and a single genus Sphaeromyxa.

Methods

In the present study, we examine eelpout from the genus Lycodes from Iceland for the presence of myxosporean parasites in the gall bladder and perform morphological and DNA studies.

Results

A novel myxosporean, Sphaeromyxa lycodi n. sp., was identified in the gall bladders of five of the six species of Lycodes examined, with a prevalence ranging from 29 - 100%. The coelozoic plasmodia are large, polysporous and contain disporic pansporoblasts and mature spores which are arcuate. The pyriform polar capsules encase long and irregularly folded ribbon-like polar filaments. Each spore valve has two distinct ends and an almost 180° twist along the relatively indistinct suture line. The single sporoplasm is granular with two nuclei. Sphaeromyxa lycodi is phylogenetically related to other arcuate sphaeromyxids and is reproducibly placed with all known sphaeromyxids and forms part of a robustly supported clade of numerous myxosporean genera which infect the hepatic biliary systems of a wide range of hosts.

Conclusions

Sphaeromyxa lycodi is a common gall bladder myxosporean in eelpout of the genus Lycodes from Northern Iceland. It has characteristics typical of the genus and develops arcuate spores. Molecular phylogenetic analyses confirm that sphaeromyxids form a monophyletic group, subdivided into straight and arcuate spore forms, within the hepatic biliary clade that infect a wide range of freshwater associated animals. The ancestral spore form for the hepatic biliary clade was probably a Chloromyxum morphotype; however, sphaeromyxids have more recently evolved from an ancestor with a spindle-shaped Myxidium spore form. We recommend that the suborder Sphaeromyxina is suppressed; however, we retain the family Sphaeromyxidae and place it in the suborder Variisporina.