Higuchi Tomihiko, Tanaka Kentaro, Shirai Kotaro, Yuyama Ikuko, Mezaki Takuma, Takahata Naoto, Sano Yuji
Atmosphere and Ocean Research Institute, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba, 277-8564, Japan.
Faculty of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki, 305-8577, Japan.
Environ Microbiol Rep. 2021 Apr;13(2):98-103. doi: 10.1111/1758-2229.12908. Epub 2020 Nov 30.
Although sulfate ions are the main form of sulfur in the ocean, there is limited knowledge on their use by living organisms. Stable isotope labelling and NanoSIMS analysis were used in this study to clarify how sulfate, in seawater, is assimilated by corals and zooxanthellae at the cellular level. Aposymbiotic and symbiotic coral juveniles from the genus Acropora were incubated for 2 days in filtered seawater with S-labelled sulfate. Further, the labelled corals were incubated for additional 2 days in natural seawater. Mapping of sulfur isotopes ( S/ S) showed that the 'hotspots' were enriched in S on a sub-micro level and were heterogeneously distributed in the coral soft tissues. Specifically, S hotspots were found in both the symbiotic zooxanthellae and coral host tissues. In aposymbiotic corals, S was detected in the tissues, indicating that the host corals directly assimilated the sulfate ions without any aid from the zooxanthellae. Even after 2 days in normal seawater, the S label was clearly seen in both symbiotic and aposymbiotic corals, indicating that the assimilated sulfur was retained for at least 2 days.
尽管硫酸根离子是海洋中硫的主要存在形式，但关于生物体对其利用的了解有限。本研究采用稳定同位素标记和纳米二次离子质谱分析，以阐明海水中的硫酸根如何在细胞水平上被珊瑚和虫黄藻同化。将来自鹿角珊瑚属的无共生关系和有共生关系的珊瑚幼体在含有硫标记硫酸根的过滤海水中孵育2天。此外，将标记后的珊瑚在天然海水中再孵育2天。硫同位素（³⁴S/³²S）图谱显示，“热点”在亚微观水平上富集了³⁴S，并且在珊瑚软组织中呈不均匀分布。具体而言，在共生虫黄藻和珊瑚宿主组织中均发现了³⁴S热点。在无共生关系的珊瑚中，在组织中检测到了³⁴S，这表明宿主珊瑚在没有虫黄藻任何帮助的情况下直接同化了硫酸根离子。即使在正常海水中孵育2天后，在有共生关系和无共生关系的珊瑚中都能清楚地看到³⁴S标记，这表明同化的硫至少保留了2天。
