DNA identification of ciliates associated with disease outbreaks in a New Zealand marine fish hatchery

Characterization of the complete mitochondrial genome of Miamiensis avidus causing flatfish scuticociliatosis

Miamiensis avidus is a parasitic pathogen that causes the disease scuticociliatosis in teleost fish species. It is a ciliate and a free-living marine protozoan belonging to the order Philasterida, subclass Scuticociliatida, class Oligohymenophorea, and phylum Ciliophora. The complete mt-genome of M. avidus was linear and 38,695 bp in length with 47 genes, including 40 protein-coding genes, two ribosomal RNA (rRNA) genes, and five transfer RNA (tRNA) genes. Of these, 20 genes typically belong to the clusters of orthologous groups, playing roles in energy production and conversion, translation, ribosomal structure and biogenesis, and defense mechanisms. This is the first report of sequencing and characterization of the mt-genome of M. avidus, which was observed to be linear and possessing the typical ciliate mitochondrial genome organization and phylogenetic relationships. Remarkable differences were observed between M. avidus and other ciliates in the mitochondrially encoded rRNAs, extensive gene loss in ribosomal genes and tRNAs, terminal repeat sequences, and stop codon usage. A comparative and phylogenetic analysis of M. avidus and Uronema marinum of the order Hymenostomatida, which is most closely related to the order Philasterida, signified the promise of the mitogenome data of M. avidus as a valuable genetic marker in species detection and taxonomic research. The present study has potential applications in epidemiological studies and host-parasite interaction investigations facilitating disease control.

Antiparasitic potential of ethanolic extracts of Carpesii Fructus against Miamiensis avidus in hirame natural embryo cell line and their effects on immune response- and biotransformation-related genes

Scuticociliatosis, caused by Miamiensis avidus, is a severe parasitic disease affecting marine organisms, particularly Paralichthys olivaceus. The aim of this study was to assess the antiparasitic potential of ethanolic extracts of Carpesii Fructus (EECF), the dried fruit of Carpesium abrotanoides L., which is used in traditional Chinese medicine, in vitro. We found that 50%, 70%, and 100% EECF induced morphological changes in M. avidus, including reduced motility, cell shrinkage, and lysis. Nearly 100% cell lysis was observed in M. avidus after 2 h of treating with 100% EECF. After 24 h, the survival rates of M. avidus treated with 100%, 70%, and 50% EECF were 10%, 20%, and 30%, respectively. Additionally, the mRNA levels of immune response-related (IL-1β, IL-8, TNF-α, and CD8-α) and biotransformation-related (CYP1A, CYP1B, CYP3A4, and UGT2B19) genes increased with 70% and 100% EECF treatment and decreased with 50% EECF treatment following pretreatment with concanavalin A. The viability of hirame natural embryo (HINAE) cells was reduced by 50%, 70%, and 100% EECF (100 mg/L) and was between 67 and 80%. The IC₅₀ values of 50%, 70%, 90%, and 100% EECF in HINAE cells were 102.3, 42.93, 39.15, and 38.39 mg/L, respectively. These results indicated that 50% EECF was less toxic to HINAE cells than 70% or 100% EECF, while still exhibiting antiparasitic activity against M. avidus. Therefore, we demonstrated the role of EECF as a natural antiparasitic agent against M. avidus. Our findings suggest that Carpesii Fructus has potential use as an antiparasitic agent in the aquaculture industry.

Comparison of mitochondrial genome and development of specific PCR primers for identifying two scuticociliates, Pseudocohnilembus persalinus and Uronema marinum

Background

Pseudocohnilembus persalinus and Uronema marinum (Ciliophora, Scuticociliatia), as parasitic scuticociliatid ciliates, were isolated from Scophthalmus maximus and Takifugu rubripes, respectively, in our previous studies. These ciliates are morphologically very similar; hence, it is difficult to identify specific scuticociliate species using traditional classification methods for performing taxonomic research and disease control studies.

Methods

We annotated the mitochondrial genomes of these two scuticociliates on the basis of previous sequencing, including analyses of nucleotide composition, codon usage, Ka/Ks, and p-distance. We also compared the nucleotide and amino acid similarity of the mitochondrial genomes of P. persalinus, U. marinum, and other 12 related ciliates, and a phylogenetic tree was constructed using 16 common genes. We chose the nad4 and nad7 genes to design specific PCR primers for identification.

Results

P. persalinus and U. marinum were found to have a close evolutionary relationship. Although codon preferences were similar, differences were observed in the usage of codons such as CGA, CGC, and GTC. Both Ka/Ks and p-distance were less than 1. Except for yejR, ymf57, ymf67, and ymf75, the amino acid sequence similarity between P. persalinus and U. marinum was greater than 50%.

Conclusions

The mitochondrial genomes of P. persalinus and U. marinum were thoroughly compared to provide a reference for disease prevention and control. The specific PCR primers enabled us to identify P. persalinus and U. marinum rapidly and accurately at the molecular level, thus providing a basis for classification and identification.

Graphic abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-04821-3.

Scuticociliatosis caused by Uronema sp. in ten different ornamental aquarium reef fish in Brazil

Scuticociliatosis, caused by an opportunistic ciliate protozoan, is responsible for significant economic losses in marine ornamental fish. This study reports the occurrence of Uronema spp., parasitizing ten species of marine reef fish at an ornamental fish wholesaler: Blue green damselfish (Chromis viridis), Vanderbilt's Chromis (Chromis vanderbilti), Pennant coralfish (Heniochus acuminatus), Threespot angelfish (Apolemichthys trimaculatus), Goldspotted angelfish (Apolemichthys xanthopunctatus), Sea goldie (Pseudanthias squamipinnis), Orchid dottyback (Pseudochromis fridmani), Threadfin butterflyfish (Chaetodon auriga), Vagabond butterflyfish (Chaetodon vagabundus), and Bluecheek butterflyfish (Chaetodon semilarvatus). Diseased fish showed disorders such as hemorrhages and ulcerative lesions on the body surface. Histopathological analysis of the muscle, liver, gut, kidney, spleen, gills, and stomach revealed hemorrhages and degeneration of muscle fiber, vacuolar degeneration of hepatocyte, inflammatory process and granuloma in the liver, atrophy of intestinal villi, inflammatory process and granuloma in the kidney, melanomacrophage centers, as well as inflammatory process in the spleen, epithelial cells hyperplasia and granuloma formation in the gills, and vacuolar degeneration and eosinophils in the stomach. Due to the severity of the disease, it is necessary to implement biosecurity measures with rapid and accurate diagnosis to minimize the risk of economic losses caused by Uronema spp.

First report of scuticociliatosis caused by Uronema sp. in ornamental reef fish imported into Brazil

Abstract Scuticociliatosis, which is caused by an opportunistic ciliate protozoan, is responsible for significant economic losses in marine ornamental fish. This study reports the occurrence of Uronema sp., which was found to be parasitizing three species of marine reef fish imported into Brazil and maintained in quarantine: Vanderbilt’s Chromis (Chromis vanderbilti), blue-green damselfish (Chromis viridis), and sea goldie (Pseudanthias squamipinnis). During the quarantine period, some fish presented with behavioral disorders and hemorrhages and ulcerative lesions on the body surface. Histopathological analysis showed hemorrhages, inflammation comprising mononuclear and granular cells in the skeletal muscle, and necrosis of the skin and the secondary lamellae of the gills, and parasites were also observed in the renal capsule. The absence of transboundary measures available to prevent the occurrence of ornamental fish diseases is also discussed.

New data on flatfish scuticociliatosis reveal that Miamiensis avidus and Philasterides dicentrarchi are different species

Scuticociliatosis is a severe disease in farmed flatfish. However, the causative agent is not always accurately identified. In this study, we identified two isolates of scuticociliates from an outbreak in cultured fine flounder Paralichthys adspersus. Scuticociliate identification was based on morphological data, examination of life stages and the use of molecular approaches. The isolates were compared with a strain of Philasterides dicentrachi from turbot Scophthalmus maximus and with a strain deposited in the American Type Culture Collection as Miamiensis avidus ATCC® 50180™. The use of morphological, biological and molecular methods enabled us to identify the isolates from the fine flouder as P. dicentrarchi. Comparison of P. dicentrachi isolates and M. avidus revealed some differences in the buccal apparatus. Unlike P. dicentrarchi, M. avidus has a life cycle with three forms: macrostomes (capable of feeding on P. dicentrarchi), microstomes and tomites. Additionally, we found differences in the 18S rRNA and α- and β-tubulin gene sequences, indicating that P. dicentrarchi and M. avidus are different species. We therefore reject the synonymy/conspecificity of the two taxa previously suggested. Finally, we suggest that a combination of morphological, biological, molecular (by multigene analysis) and serological techniques could improve the identification of scuticociliates parasites in fish.

Systemic Scuticociliatosis (Philasterides dicentrarchi) in Sharks

Scuticociliatosis is an economically important, frequently fatal disease of marine fish in aquaculture, caused by histophagous ciliated protozoa in the subclass Scuticociliatida of the phylum Ciliophora. A rapidly lethal systemic scuticociliate infection is described that affected aquarium-captive zebra sharks ( Stegostoma fasciatum), Port Jackson sharks ( Heterodontus portusjacksoni), and a Japanese horn shark ( Heterodontus japonicus). Animals died unexpectedly or after a brief period of lethargy or behavioral abnormality. Gross findings included necrohemorrhagic hepatitis and increased volumes of celomic fluid. Histologically, 1 or more of a triad of necrotizing hepatitis, necrotizing meningoencephalitis, and thrombosing branchitis were seen in all cases, with necrotizing vasculitis or intravascular fibrinocellular thrombi. Lesions contained variably abundant invading ciliated protozoa. Molecular identification by polymerase chain reaction from formalin-fixed tissues identified these as the scuticociliate Philasterides dicentrarchi (syn. Miamiensis avidus), a novel and potentially emergent pathogen in sharks.

In vivo innate immune responses of groper (Polyprion oxygeneios) against Miamiensis avidus infection and lack of protection following dietary vitamin C administration

Scuticociliates are extracellular histophagous parasites that affect farmed fish worldwide. One of the most common pathogenic species is Miamiensis avidus, a pathogen of New Zealand groper (Polyprion oxygeneios). The aim of this study was to characterise both the host (groper)-parasite (M. avidus) immune interactions and the possible protective role of dietary sodium ascorbate. Head-kidney leucocytes (HKLs) from naturally infected adult groper showed decreased respiratory burst response and peroxidase (Px) levels than healthy individuals. Infected groper also had significantly higher serum Px levels compared to controls. Myeloperoxidase (MPO) was inhibited in the head-kidney (HK) whereas MPO(+) cells were observed in the skin and muscle lesions. The inhibition of the innate immune responses was further studied in experimental infections with M. avidus, which confirmed depletion of Px inside leucocytes and marked increases in serum Px in infected individuals. Groper juveniles were fed a diet supplemented with sodium ascorbate (Vitamin C) (2g Kg(-1)) for 21 days and then challenged by subcutaneous injection or immersion exposure with live M. avidus cells. No protection was observed in the sodium ascorbate fed groper compared to the control diet following challenge by either injection or immersion. In vitro assays showed that sodium ascorbate itself results in the inhibition of Px and respiratory burst of groper HKLs, supporting the results obtained in vivo. Our results show that histophagous protozoa such as M. avidus hamper innate immune defences of fish hosts and that dietary sodium ascorbate does not protect groper against experimental infection with this parasite.

Characterization of acid phosphatases from marine scuticociliate parasites and their activation by host's factors

Scuticociliates are histophagous marine parasites that cause mortality in fish. Acid phosphatases (AcPs) are considered virulence factors and they are used by different parasites to dephosphorylate host molecules. The aim of this work was to characterize the AcPs from 3 scuticociliate species, Uronema marinum, Miamiensis avidus and Parauronema virginianum, which parasitize marine finfish species. We identified AcP activity (pH 5.2) with differential cellular distribution in the 3 parasite species. Native gel electrophoresis of ciliate lysates revealed the presence of 1 high molecular weight AcP activity band in M. avidus (tartrate-sensitive), several low molecular weight AcPs in U. marinum and 1 low molecular weight band only in P. virginianum (tartrate-resistant). Scuticociliate AcP was inhibited by specific inhibitors of tyrosine protein phosphatases. AcP decreased upon starvation but rapid reactivation occurred following exposure to skin mucus. Groper (Polyprion oxygeneios) peripheral blood leucocytes (PBLs) and, to a lesser extent, red blood cells, also increased AcP activity. Protein tyrosine phosphatase PTP1b was primarily detected in the plasma membrane of M. avidus and ingestion of groper PBLs upregulated its expression. M. avidus recovered from experimentally infected groper had greater levels of PTP1b expression than the injected suspension. The present results highlight the importance of PTPs in histophagous parasites and their interaction with fish host's factors.

In vitro culture and cryopreservation of Uronema marinum isolated from farmed New Zealand groper (Polyprion oxygeneios)

An in vitro culture method was developed for the ciliated protozoa Uronema marinum isolated from New Zealand aquacultured groper (Polyprion oxygeneios). Both formulated media and sterile seawater supplemented with homogenised fish tissue as a food source supported growth of U. marinum achieving cell densities of up to 1 x 10(5)cells/mL in culture. A cryopreservation method based on a cryomix formula of 20% glycerol, 10% fetal bovine serum and 70% cultured U. marinum, incorporating a slow freeze method to -80 degrees C, then liquid nitrogen storage, allowed cryogenic storage of cells and successful re-culture up to 12 months in storage.