Ultrastructure and molecular diagnosis of Spironucleus salmonis (Diplomonadida) from rainbow trout Oncorhynchus mykiss in Germany

• Published in: Diseases of aquatic organisms Vol. 75; no. 1; pp. 37 - 50
• Main Authors: REZA SAGHARI FARD, M, JØRGENSEN, Anders, STERUD, Erik, BLEISS, Wilfrid, POYNTON, Sarah L
• Format: Journal Article
• Language: English
• Published: Oldendorf Inter-Research 29-03-2007
• Subjects: Animal aquaculture; Animal productions; Animals; Base Sequence; Biological and medical sciences; Diplomonadida; Diplomonadida - genetics; Diplomonadida - isolation & purification; Diplomonadida - pathogenicity; Diplomonadida - ultrastructure; DNA Primers - chemistry; Fish Diseases - epidemiology; Fish Diseases - parasitology; Fish Diseases - pathology; Fundamental and applied biological sciences. Psychology; Genes, rRNA - genetics; Germany - epidemiology; Hexamita salmonis; Intestines - parasitology; Molecular Sequence Data; Oncorhynchus mykiss; Oncorhynchus mykiss - parasitology; Phylogeny; Pisciculture; Protozoan Infections - diagnosis; Protozoan Infections - epidemiology; Protozoan Infections - pathology; Protozoan Infections, Animal; Sequence Alignment; Spironucleus; Vertebrate aquaculture; Europe; Germany; Asia; North America; Protozoa; Scanning electron microscopy; Edible fish; ssu rDNA; Ribosomal DNA; Diagnosis (taxonomy); Parasite; Diplomonadida; Zoopathogen; Sequence; Oncorhynchus mykiss; Vertebrata; Transmission electron microscopy; Ultrastructure; Pathogenic; Pisces; Morphology; Diplomonad; Rainbow trout; Specific identification; Molecular systematics; Diagnosis; Flagellate; Spironucleus salmonis
• ISSN: 0177-5103; 1616-1580
• DOI: 10.3354/dao075037

Diplomonad flagellates infect a wide range of fish hosts in aquaculture and in the wild in North America, Asia and Europe. Intestinal diplomonad infection in juvenile farmed trout can be associated with morbidity and mortality, and in Germany, diplomonads in trout are commonly reported, and yet are poorly characterised. We therefore undertook a comprehensive study of diplomonads from German rainbow trout Oncorhynchus mykiss, using scanning and transmission electron microscopy, and sequencing of the small subunit (ssu) rRNA gene. The diplomonad was identified as Spironucleus salmonis, formerly reported from Germany as Hexamita salmonis. Our new surface morphology studies showed that the cell surface was unadorned and a caudal projection was present. Transmission electron microscopy facilitated new observations of functional morphology, including vacuoles discharging from the body surface, and multi-lobed apices of the nuclei. We suggest the lobes form, via hydrostatic pressure on the nucleoplasm, in response to the beat of the anterior-medial flagella. The lobes serve to intertwine the nuclei, providing stability in the region of the cell exposed to internal mechanical stress. The ssu rRNA gene sequence clearly distinguished S. salmonis from S. barkhanus, S. salmonicida, and S. vortens from fish, and can be used for identification purposes. A 1405 bp sequence of the ssu rRNA gene from S. salmonis was obtained and included in a phylogenetic analysis of a selection of closely related diplomonads, showing that S. salmonis was recovered as sister taxon to S. vortens.