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Diseases of Aquatic Organisms

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DAO 54:209-217 (2003)  -  doi:10.3354/dao054209

Mikrocytos roughleyi taxonomic affiliation leads to the genus Bonamia (Haplosporidia)

N. Cochennec-Laureau1,4,*, K. S. Reece2, F. C. J. Berthe1, P. M. Hine3

1Institut Français de Recherche pour l¹Exploitation de la Mer (IFREMER), Laboratoire de Génétique et Pathologie, PO Box 1346, 17390 La Tremblade, France
2Virginia Institute of Marine Science (VIMS), Aquaculture Genetics and Breeding Technology Center, Gloucester Point, Virginia 23062, USA
3Aquatic Animal Diseases, National Centre for Disease Investigation, Ministry of Agriculture and Fisheries (MAF) Operations, PO Box 40-742, Upper Hutt, 6007 Wellington, New Zealand
4Present address: IFREMER, Laboratoire d¹Aquaculture Tropicale, BP 7004, 98719 Taravao, French Polynesia

ABSTRACT: Microcell-type parasites of oysters are associated with a complex of diseases in different oyster species around the world. The etiological agents are protists of very small size that are very difficult to characterize taxonomically. Associated lesions may vary according to the host species, and their occurrence may be related to variations in tissue structure. Lesion morphology cannot be used to distinguish the different agents involved. Ultrastructural observations on Mikrocytos roughleyi revealed similarities with Bonamia spp., particularly in regard to the presence of electron-dense haplosporosomes and mitochondria, whose absence from M. mackini also indicate that M. roughleyi and M. mackini are not congeneric. A partial small subunit (ssu) rRNA gene sequence of M. roughleyi was determined. This partial sequence, 951 nucleotides in length, has 95.2 and 98.4% sequence similarities with B. ostreae and B. exitiosus ssu rDNA sequences, respectively. Polymorphisms among the ssu rDNA sequences of B. ostreae, B. exitiosus and M. roughleyi allowed identification of restriction enzyme digestion patterns diagnostic for each species. Phylogenetic analysis based on the ssu rDNA data suggested that M. roughleyi belongs in the phylum Haplosporidia and that it is closely related to Bonamia spp. On the basis of ultrastructural and molecular considerations, M. roughleyi should be considered a putative member of the genus Bonamia.

KEY WORDS: Mikrocytos roughleyi · Saccostrea glomerata · Bonamiosis · Microcell · Taxonomy · Small subunit rDNA

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