Ohishi Kazue, Yamamoto Masahiro, Tame Akihiro, Kusaka Chiho, Nagai Yukiko, Sugimura Makoto, Inoue Koji, Uematsu Katsuyuki, Yoshida Takao, Ikuta Tetsuro, Toyofuku Takashi, Maruyama Tadashi
Marine Biodiversity Research Program, and.
Department of Subsurface Geobiological Analysis and Research, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2-15 Natsushima-cho, Yokosuka, Kanagawa 237-0061, Japan;
Biol Bull. 2016 Jun;230(3):257-67. doi: 10.1086/BBLv230n3p257.
Survival of deep-sea Calyptogena clams depends on organic carbon produced by symbiotic, sulfur-oxidizing, autotrophic bacteria present in the epithelial cells of the gill. To understand the mechanism underlying this symbiosis, the development of a long-term cultivation system is essential. We cultivated specimens of Calyptogena okutanii in an artificial chemosynthetic aquarium with a hydrogen sulfide (H2S) supply system provided by the sulfate reduction of dog food buried in the sediment. We studied morphological and histochemical changes in the clams' gills by immunohistochemical and energy-dispersive X-ray analyses. The freshly collected clams contained a high amount of elemental sulfur in the gill epithelial cells, as well as densely packed symbiotic bacteria. Neither elemental sulfur nor symbiotic bacteria was detected in any other organs except the ovaries, where symbiotic bacteria, but not sulfur, was detected. The longest survival of an individual clam in this aquarium was 151 days. In the 3 clams dissected on Days 57 and 91 of the experiment, no elemental sulfur was detected in the gills. The symbiotic bacteria content had significantly decreased by Day 57, and was absent by Day 91. For comparison, we also studied the deep-sea mussel Bathymodiolus septemdierum, which harbors a phylogenetically close, sulfur-oxidizing, symbiotic bacterium with similar sulfur oxidation pathways. Sulfur particles were not detected, even in the gills of the freshly collected mussels. We discuss the importance of the proportion of available H2S and oxygen to the bivalves for elemental sulfur accumulation. Storage of nontoxic elemental sulfur, an energy source, seems to be an adaptive strategy of C. okutanii.
深海潜泥蛤的生存依赖于鳃上皮细胞内共生的、硫氧化自养细菌产生的有机碳。为了解这种共生关系的潜在机制，建立长期培养系统至关重要。我们在一个人工化学合成水族箱中培养了大潭潜泥蛤标本，该水族箱通过埋藏在沉积物中的狗粮进行硫酸盐还原提供硫化氢（H₂S）供应系统。我们通过免疫组织化学和能量色散X射线分析研究了蛤鳃的形态和组织化学变化。刚采集的蛤在鳃上皮细胞中含有大量元素硫以及密集排列的共生细菌。除卵巢外，在其他任何器官中均未检测到元素硫和共生细菌，卵巢中检测到了共生细菌，但未检测到硫。在这个水族箱中，单个蛤的最长存活时间为151天。在实验第57天和第91天解剖的3只蛤中，鳃中未检测到元素硫。到第57天，共生细菌含量显著下降，到第91天已不存在。作为对照，我们还研究了深海贻贝Septemdierum Bathymodiolus，它含有一种系统发育关系密切、硫氧化共生细菌，其硫氧化途径相似。即使在刚采集的贻贝的鳃中也未检测到硫颗粒。我们讨论了可用H₂S和氧气的比例对双壳贝类积累元素硫的重要性。储存无毒的元素硫作为一种能量来源，似乎是大潭潜泥蛤的一种适应性策略。
