Symbiotic adaptation to hadal environment -Metabolic functions of intracellular symbions from the hadal thyasirid clam Marithyas hadalis-

大花毛蛤（Maorithyashadalis）是日本海沟7，200 ~ 7，400米深渗漏环境中的一个重要物种。在鳃组织中发现了两种不同类型的内共生菌，并观察到两种内共生菌之间的空间分配。探讨了海蛤对深海还原环境的适应机制。2005年，从M.海葵鳃根据泡绵蛤Calyptogena okutanii共生体16 S核糖体RNA基因序列与泡绵蛤M. kutanii共生体16 S核糖体RNA基因序列的相似性，设计了一对特异性引物，用于泡绵蛤Calyptogena okutanii共生体SoxB基因的PCR扩增。hadalis和C.奥谷共生体2007年，从M. hadalis鳃使用特定的引物。因此，其中一种共生菌的硫氧化能力不仅与其繁殖有关，而且与其代谢有关。为了了解SoxB基因在宿主组织中的微分布，于2006年进行了荧光原位杂交实验。为了确定实验条件，应用了鲸落贻贝Adipicola pacifica，因为贻贝的肉个体很容易从我们的水族馆获得。确定了最佳的固定时间和固定剂。FISH实验需要肉标本，但没有机会收集新的样本，因为只有一只到达M. hadalis栖息地，已经失去了。新型深潜器的研制可以解决这一问题。海洋共生体了解无脊椎动物与细菌之间广泛分布的化能共生体对于了解它们的地理分布和进化具有重要意义。

The thyasrid clam Maorithyas hadalis is a conspicuous species in seep environments at depths of 7, 200-7,400 meters in the Japan Trench. Two distinct phylotypes of endosymbiotic bacteria were shown and spatial partitioning between the phylotypes was observed within the gill tissues.The purpose of this study was to clarify the metabolic functions of the symbionts of M. hadalis and to understand the adaptation mechanism of the thyasirid clam to its hadal reducing environment. In 2005, detection of genes regarding sulfur oxidation was conducted from M. hadalis gills. The specific primers for PCR amplification of SoxB gene of symbionts from the vesicomyid clam Calyptogena okutanii were designed because of the similarity of 16S ribosomal RNA gene sequences of between the M. hadalis and C. okutanii symbionts. In 2007, SoxB gene was successfully amplified from the total extracted DNA of M. hadalis gills using the specific primers. Therefore, the sulfur oxidizing capability of one of the symbionts was supported by not only phylogeny but also metabolism.For understanding the microdistribution of the SoxB gene in the host tissue, fluorescence in situ hybridization experiments were conducted in 2006. To determine the experimental conditions, the whale-fall mussel Adipicola pacifica was applied because flesh individuals of the mussel were easily available from our aquaria. The optimum conditions were set for fixation time and fixative. Flesh specimens were required for FISH experiments but there was no chance to collect new samples because the ROV Kaiko, which was the only ROV to reach the M. hadalis habitat, had been lost. Developments of new deep-diving ROV can be dissolve this problem.This study showed the metabolic function regarding sulfur oxidation in the M. hadalis symbionts. It is important to recognize the wide distribution range of chemosynthetic symbioses between invertebrates and bacteria for understanding of their biogeography and evolution.