Genetical ecology of microalgae causing Ciguatera in Taihiti

在许多热带珊瑚礁地区，已知“雪卡特纳”是一种由摄入有毒海洋鱼类引起的人类疾病。这些毒素似乎来自在法属波利尼西亚雪卡毒流行地区发现的一种附生底栖鞭毛藻Gambierdisucus toxicus。雪卡毒素的化学和毒理学研究主要集中在雪卡毒素上，但关于雪卡毒素生物相的研究很少。本研究力求：1。大溪地岛毒田鼠种群及分布概况，2。2 .毒蕈菌和细菌群落如何附着在巨藻Jania （Rhodophyta）上并相互作用；阐明毒虫的系统发育关系，区分毒虫种群。研究结果如下：(1) 1993-1994年12月至1月，塔希提岛两个珊瑚礁站发生了与贾尼亚有关的毒蝇小华。毒虫细胞分布在同一站点，细胞密度在10 ~ 10^3个/g之间。大多数毒g.s毒虫细胞通常在Jania群体中游动，并以鞭毛暂时附着在Jania分支上。一些与Jania相关的细菌刺激了g.s toxicus的生长，并可能影响g.s toxicus的发生。(2)附生鞭毛藻毒g.g .toxicus的游动受到来自Jania的胞外物质的刺激。在相似的珊瑚礁生境中生长的Galaxaura、Amphiroa、Corallina （rhoophyhya）和haalimeda（绿藻门）也发现了对毒蝇的刺激作用。(3)测定了塔希提岛不同站点分离的两株毒菌18SrRNA基因的核苷酸序列，阐明了它们在鞭毛类动物中的系统发育关系。结果表明，毒弧菌与引起麻痹性贝类中毒的有毒亚历山Alexandrium形成一个集群，具有特定的进化地位。通过rDNA内转录间隔区和5.8S区限制性内切片段长度多态性分析，表明毒田鼠至少存在3个不同的种群。少

In many tropical coral reef regions, "ciguatera" has been known a human disease caused by the ingestion of toxic marine finfish. These toxins appear to originate from an epiphytic, benthic dinoflagellate found in ciguatera endemic areas of French Polynesia, Gambierdisucus toxicus. Chemical and toxicological studies of ciguatera toxins have been focused on G.toxicus, but there is little information about biological phase of this dinoflagellate. The present study sought to : 1. general survey of G.toxicus populations and distribution in Tahiti Island, 2. how G.toxicus and bacterial community attach to macroalga Jania (Rhodophyta) and interact each other, 3. to clarify the phylogenetic relationship and distinguish the population of G.toxicus. The results are as follows ;(1) A small bloom of G.toxicus priorly associated with Jania occurred from December to January in 1993-1994 in two fringing reef stations of Tahiti Island. G.toxicus cells localized even in the same station and the cell de … More nsity varied from 10-10^3 cells/g of wet algae. Most of G.toxicus cells usually swim in the Jania colony and attach temporary to the Jania branch with flagella. Some bacteria associated with Jania stimulate the growth of G.toxicus and possibly influence on G.toxicus occurrence.(2) Swimming of epiphytic dinoflagellate G.toxicus is stimulated by the extracellular substances from Jania. The stimulation activity on swimming of G.toxicus was also found in Galaxaura, Amphiroa, Corallina (Rhodophyta) and Halimeda (Chlorophyta) grwon in similar coral reef habitats.(3) The nucleotide sequences of 18SrRNA gene were determined from two strain of G.toxicus isolated from different stations in Tahiti Island to clarify their phylogenetic relationship in dinoflagellates. The result indicate that G.toxicus make a cluster with toxic Alexandrium causing paralytic shellfish poisoning and has a specific evolutionary position. It is suggested that at least three different populations are present in G.toxicus by restriction fragment length polymorphism analysis of rDNA inernal transcribed spacer and 5.8S regions. Less