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Title: Small subunit ribosomal RNA sequence links the myxospore stage of Henneguya mississippiensis n. sp. from channel catfish Ictalurus punctatus to an actinospore released by the benthic oligochaete Dero digitata

Author
item ROSSER, THOMAS - Mississippi State University
item GRIFFIN, MATT - Mississippi State University
item Quiniou, Sylvie
item KHOO, LESTER - Mississippi State University
item GREENWAY, TERRENCE - Mississippi State University
item WISE, DAVID - Mississippi State University

Submitted to: Parasitology Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/22/2015
Publication Date: 4/1/2015
Citation: Rosser, T.G., Griffin, M.J., Quiniou, S., Khoo, L.H., Greenway, T.E., Wise, D.J. 2015. Small subunit ribosomal RNA sequence links the myxospore stage of Henneguya mississippiensis n. sp. from channel catfish Ictalurus punctatus to an actinospore released by the benthic oligochaete Dero digitata. Parasitology Research. 114:1595-1602.

Interpretive Summary: A novel species of Henneguya infecting the gills of channel catfish is described. Molecular and morphological methods were used to characterize the myxospore stage from naturally infected farm-raised channel catfish. Sequencing of the isolate and a subsequent search of the National Centers for Biotechnology Information nucleotide database linked this myxospore stage to an actinospore stage released by the benthic oligochaete Dero digitata, molecularly confirming the complex parasitic life cycle. Phylogenetic analysis indicated this species grouped with the other known Henneguya that parasitize ictalurid fish in North America, specifically H. adiposa and H. ictaluri. The unique myxospore morphology, pseudocyst location, and genetic sequence led us to propose this as a novel species, H. mississippiensis n. sp.

Technical Abstract: There are more than 200 species of Henneguya described from fish. Of these, only three life cycles have been determined, identifying the actinospore and myxospore stages from their respective hosts. Two of these life cycles involve the channel catfish (Ictalurus punctatus) and the freshwater oligochaete Dero digitata. Herein we molecularly confirm the life cycle of a previously undescribed Henneguya sp. by matching 18S rRNA gene sequence of the myxospore stage from channel catfish with the previously described actinospore stage (Aurantiactinomyxon mississippiensis) from D. digitata. Gill tissue from naturally infected channel catfish contained pseudocysts restricted to the apical end of the primary lamellae. Myxospores were morphologically consistent with Henneguya spp. from ictalurid fishes in North America. The spores measured 48.8 ± 4.8 µm (range = 40.7-61.6 µm) in total spore length. The lanceolate spore body was 17.1 ± 1.0 µm (14.4-19.3 µm) in length and 5.0 ± 0.3 µm (4.5-5.5 µm) in width. The two polar capsules were 6.2 ± 0.4 µm (5.8-7.0 µm) long and 5.0 ± 0.3 µm (4.5-5.5 µm) wide. Polar capsules contained 8-9 coils in the polar filament. The two caudal processes were of equal length, measuring 31.0 ± 4.1 µm (22.9-40.6 µm). The 1980 bp 18S rRNA gene sequence obtained from two excised cysts shared 99.4% similarity (100% coverage) to the published sequence of A. mississippiensis, an actinospore previously described from D. digitata. The sequence similarity between the myxospore from channel catfish and actinospore from D. digitata suggests they are conspecific, representing alternate life stages of H. mississippiensis n. sp.