Ultrastructure of Mikrocytos mackini, the cause of Denman Island disease in oysters Crassostrea spp. and Ostrea spp. in British Columbia, Canada

Type Article
Date 2001-08
Language English
Author(s) Hine P, Bower S, Meyer G, Cochennec NathalieORCID, Berthe Franck
Affiliation(s) IFREMER, Lab Genet & Pathol, F-17390 La Tremblade, France.
Fisheries & Oceans Canada, Biol Sci Branch, Pacific Biol Stn, Nanaimo, BC V9R 5K6, Canada.
Source Diseases of aquatic organisms (0177-5103) (Inter-Research), 2001-08 , Vol. 45 , N. 3 , P. 215-227
WOS© Times Cited 26
Keyword(s) Denman Island disease, Amitochondriate protozoan, Ultrastructure, Crassostrea gigas, Mikrocytos mackini
Abstract An ultrastructural study was carried out on Mikrocytos mackini, the cause of Denman Island disease in Pacific oysters Crassostrea gigas in western Canada. Three forms were identified, quiescent cells (QC), vesicular cells (VC) and endosomal cells (EC), QC occurred in the vesicular connective tissue (VCT), haemocytes (hyalinocytes), adductor and heart myocytes, and extracellularly, They had a central round to ovoid nucleus, <7 cisternae of inactive nuclear membrane-bound Golgi, few vesicles and lysosome-like bodies. VC were rarely extracellular and usually occurred in adductor and heart myocytes, in close association with host cell mitochondria. The contents of the host cell mitochondria appeared to pass through a tubular extension into the cytoplasm of the parasite. Cytoplasmic vesicles resembled the tubular structure in appearance and size. EC occurred in the VCT, in haemocytes and extracellularly. They had a dilated nuclear membrane, sometimes containing a looped membranous structure that appeared to derive from the nucleus, and pass into the cytoplasm. A well-developed anastomosing endoplasmic reticulum connected the nuclear and plasma membranes, and endosomes were present in the cytoplasm. QC and EC cells were frequently observed tightly against, or between, the nuclear membranes of the host cell.-Few organelles occurred in all forms of M mackini, especially QC. The lack of organelles found in most eukaryotic cells, including mitochondria or their equivalents, may be due to obligate parasitism and the utilization of host cell organelles reducing the need for parasite organelles. Alternatively, perhaps M, mackini is a primitive eukaryote. Although phylogenetic affinities could not be determined, it is not a haplosporidian. A developmental cycle is proposed from these findings.
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Hine P, Bower S, Meyer G, Cochennec Nathalie, Berthe Franck (2001). Ultrastructure of Mikrocytos mackini, the cause of Denman Island disease in oysters Crassostrea spp. and Ostrea spp. in British Columbia, Canada. Diseases of aquatic organisms, 45(3), 215-227. Open Access version : https://archimer.ifremer.fr/doc/00000/815/