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1 May 2006 Localization of Symbiotic Cyanobacteria in the Colonial Ascidian Trididemnum miniatum (Didemnidae, Ascidiacea)
Euichi Hirose, Mamiko Hirose, Brett A. Neilan
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Trididemnum miniatum is a colonial ascidian harboring the photosymbiotic prokaryote Prochloron sp. These bacterial cells are located in the tunic of the host animal. The present study revealed, by ultrastructural analysis, that the Prochloron cells were exclusively distributed and proliferated in the tunic. They were shown to be embedded in the tunic matrix and to have no direct contact with ascidian cells. Some tunic cells of the ascidians, however, did phagocytize and digest the symbiont. Round cell masses were sometimes found in the tunic and appeared to consist of disintegrating cyanobacterial cells. The thoracic epidermis of ascidian zooids was often digitated, and the epidermal cells extended microvilli into the tunic. Since there were no Prochloron cells in the alimentary tract of the ascidian zooids, the photosymbionts would not be considered part of the typical diet of the host ascidians. Thin layer chromatography showed that the symbionts possessed both chlorophyll a and b, while a 16S rRNA gene phylogeny supported the identification of the photosymbiont of T. miniatum as Prochloron sp.

Euichi Hirose, Mamiko Hirose, and Brett A. Neilan "Localization of Symbiotic Cyanobacteria in the Colonial Ascidian Trididemnum miniatum (Didemnidae, Ascidiacea)," Zoological Science 23(5), 435-442, (1 May 2006).
Received: 2 February 2006; Accepted: 1 March 2006; Published: 1 May 2006
Coral reef
didemnid ascidian
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