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First report of Hexamita nelsoni in blue mussel (Mytilus edulis): morphology, phylogeny, and host-parasite interaction
(Burki lab)ORCID iD: 0000-0003-1733-4085
(English)Manuscript (preprint) (Other academic)
Abstract [en]

 Bivalve diseases caused by protozoan parasitic infection are monitored by coordinated surveillance programs across European member countries. These routine monitorings of bivalve health, however, only survey a few relatively well known parasites, which may leave undetected a range of lesser known opportunistic protozoan agents. Under increased stress, for example due to shifting environmental conditions affecting water quality and nutrient access, these opportunistic parasites may develop pathogenicity impacting reproduction or growth and therefore decreasing the success and future development of aquaculture or wild population sustainability. During routine histopathological surveillance of blue mussels in Sweden, we noticed cryptic lesions in the adductor muscle in high prevalence over a period ranging from 2017 to 2022. These lesions suggested cell infiltration and degenerative changes in the muscle tissues. In this study, we report on the isolation, identification, and culture of the protistan cells likely responsible for at least some of these lesions. Using histology and cytology, molecular phylogeny, and catalyzed reporter deposition fluorescence in situ hybridization (CARD-FISH), we show that the cells correspond to the H. nelsoni sequence initially isolated from oysters. We also reveal the presence of H. nelsoni in the digestive glands and mantel, and that this parasite might be horizontally transmitted from adult to larvae via infections within gonads, ovaries. This study represents the first report of H. nelsoni in blue mussel.

Keywords [en]
Mytilus edulis, parasite, protists, Diplomonada, Hexamita nelsoni, adductor muscle, ovarie, digestive gland, mantel, histology, CARD-FISH, phylogeny
National Category
Natural Sciences
Research subject
Biology with specialization in Systematics
Identifiers
URN: urn:nbn:se:uu:diva-538803OAI: oai:DiVA.org:uu-538803DiVA, id: diva2:1899729
Funder
Swedish Research Council Formas, 2017-01197Available from: 2024-09-20 Created: 2024-09-20 Last updated: 2024-09-20
In thesis
1. Morphological and molecular studies of bivalves to assess the hidden diversity of protistan parasites: Investigations of cryptic diseases in shellfish
Open this publication in new window or tab >>Morphological and molecular studies of bivalves to assess the hidden diversity of protistan parasites: Investigations of cryptic diseases in shellfish
2024 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis investigates the host - parasitic relationships in mussel, started by investigating unexplained massmortalities in freshwater mussels, Margaritifera margaritifera. By compiling geodata with symptoms and histopathology (Paper 1). In Paper 2, I continued on these investigations, describing a parasitic gregarines in host. Using in situ hybridization (ISH) and ultrastructural analysis, we linked this gregarine to host detected lesions. To investigate fixed sampled, we used CARD-FISH demonstrating new patterns of parasitic infiltration of gonads. (Paper 3). In marine environments, protist parasites have been throughly documented, though several lesions remain unexplained. Using cell culture, we isolated Hexamita nelsoni linking this protist with blue mussels lesions in muscle & gonads, using CARD-FISH (Paper 4). The largest threat towards marine mussel aquaculture are Ascetosporean parasites, not culturable, requiring alternative methods for genomic studies. We used, density gradient filtration to concentrate Marteilia pararefringens and Bonamia ostreae from infected tissues, enabling these studies, Paper 5.

Abstract [sv]

Mitt doktorandsarbete undersöker relationen mellan musslan och dessa parasiter. Arbetet startade med studier av oförklarade massdödligheter bland sötvattens musslor, Margaritifera margaritifera, genom sammanställning av geologiska data och observerade sjukdomssymtom (Paper 1). In nästa studie (Paper 2), fortsätter vi detta genom att beskriva en ny gregarin (Apicomplexa) associerade med organförändringar. Med In situ hybridisering (ISH) och elektronmikroskopi, kunde vi koppla dessa till observerade vävnadsskador. Vidare påvisade vi olika arter av gregariner genom CARD-FISH metodik i histologiska prover och demonstrera därigenom nya mönster av parasitär infiltration (Paper 3). Mussel parasiter i marin miljö är  väldokumenterade, även om vissa organskador förblivit oförklarade. Genom cellkultur från blåmussla isolerades Hexamita nelsoni, och kopplades till observerade organskador, i muskel och gonadvävnad, med CARD-FISH (Paper 4). Det största hoten mot vattenbruk av Bivalver är Ascetosporea parasiter, som ej går at odla. För genomisk undersökning krävs andra alternativ. Med gradient filtrering  möjliggjordes koncentration av dessa celler och genomiska studier av Marteilia och Bonamia.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2024. p. 69
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 2450
Keywords
Margaritifera margaritifera, Freshwater Pearl Mussel, Mass mortality events, Gregarine, Pathology, CARD-FISH, ISH, Mytilus edulis, blåmussla, Hexamita nelsoni, phylogeny, histology
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-538623 (URN)978-91-513-2233-9 (ISBN)
Public defence
2024-11-01, Lindahlsalen, 05.01058, Evolutionsbiologiskt centrum (EBC), Norbyvägen 14, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2024-10-11 Created: 2024-09-18 Last updated: 2024-10-31

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CiteExportLink to record
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Citation style
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