Hirose Euichi, Hirose Mamiko, Neilan Brett A
Department of Chemistry, Biology and Marine Science, Faculty of Science, University of the Ryukyus, Nishhihara, Japan.
Zoolog Sci. 2006 May;23(5):435-42. doi: 10.2108/zsj.23.435.
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.
迷你三肋海鞘是一种群体海鞘，体内共生着光合原核生物原绿藻属（Prochloron sp.）。这些细菌细胞位于宿主动物的被囊中。本研究通过超微结构分析揭示，原绿藻细胞仅分布于被囊中并在其中增殖。它们被证明嵌入在被囊基质中，与海鞘细胞无直接接触。然而，一些海鞘的被囊细胞确实吞噬并消化了共生体。在被囊中有时会发现圆形细胞团，似乎由解体的蓝细菌细胞组成。海鞘幼体的胸表皮常有指状突起，表皮细胞向被囊中延伸出微绒毛。由于海鞘幼体的消化道中没有原绿藻细胞，这些光合共生体不被视为宿主海鞘典型食物的一部分。薄层色谱分析表明，共生体同时含有叶绿素a和b，而16S rRNA基因系统发育分析支持将迷你三肋海鞘的光合共生体鉴定为原绿藻属。
