Genetical ecology of microalgae causing Ciguatera in Taihiti

在许多热带珊瑚礁地区，“雪卡特拉”已被认为是一种由摄入有毒海洋鳍鱼引起的人类疾病。这些毒素似乎来自一种附生的底栖甲藻，发现于法属波利尼西亚的雪卡特拉流行区，即冈比亚毒素。对雪卡特拉毒素的化学和毒理学研究主要集中在毒藻，但关于这种甲藻生物学相的信息很少。本研究旨在：1.大溪地岛毒藻种群及分布概况；2.毒藻与细菌群落的附着和相互作用；3.阐明毒藻的系统发育关系，区分毒藻种群。结果表明：(1)1993-1994年12~1月，大溪地岛两个礁边缘站发生了一次小水华。毒素G细胞定位于同一站点和De…细胞更多的细胞密度变化在10-10^3个/g湿藻。大多数毒藻细胞通常游动于Jania菌落，并暂时附着于有鞭毛的Jania枝上。一些与水母相关的细菌刺激毒藻的生长，并可能对毒藻的发生产生影响。(2)水母胞外物质刺激附生甲藻毒藻的游泳。在相似的珊瑚礁生境中，毒藻对游泳的刺激作用也存在于Galaxaura、Amphiroa、Corallina和Halimeda(绿藻门)中。(3)对大溪地岛不同站点分离的两株毒藻的18SrRNA基因序列进行了测定，以阐明它们在甲藻中的系统发育关系。结果表明，有毒革兰氏菌与致麻性贝毒的亚历山大藻聚在一起，具有特定的进化地位。RDNA内转录间隔区和5.8S区的限制性片段长度多态性分析表明，毒蛾体内至少存在3个不同的种群。较少

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