Amoebocytes facilitate efficient carbon and nitrogen assimilation in the Cassiopea Symbiodiniaceae symbiosis

The upside-down jellyfish Cassiopea engages in symbiosis with photosynthetic microalgae that facilitate uptake and recycling of inorganic nutrients. In contrast to most other symbiotic cnidarians, algal endosymbionts in Cassiopea are not restricted to the gastroderm but are found in amoebocyte cells within the mesoglea. While symbiont-bearing amoebocytes are highly abundant, their role in nutrient uptake and cycling in Cassiopea remains unknown. By combining isotopic labelling experiments with correlated SEM and NanoSIMS imaging, we quantified the anabolic assimilation of inorganic carbon and nitrogen at the subcellular level in juvenile Cassiopea medusae bell tissue. Amoebocytes were clustered near the sub-umbrella epidermis and facilitated efficient assimilation of inorganic nutrients. Photosynthetically-fixed carbon was efficiently translocated between endosymbionts, amoebocytes and host epidermis at rates similar to or exceeding those observed in corals. The Cassiopea holobionts eff...

倒立仙女水母（Cassiopea）可与光合微藻形成共生关系，后者能够促进宿主对无机营养物的摄取与循环利用。与绝大多数其他共生刺胞动物不同，该物种体内的藻类内共生体并不局限于胃层，而是分布于中胶层内的变形细胞中。尽管携带内共生体的变形细胞丰度极高，但其在仙女水母营养摄取与循环过程中的具体作用仍不明确。本研究将同位素标记实验与关联式扫描电子显微镜（SEM）、纳米二次离子质谱成像（NanoSIMS）相结合，在亚细胞水平定量分析了幼年仙女水母伞部组织中无机碳与氮的同化代谢过程。研究结果显示，变形细胞聚集于伞下表皮附近，可高效促进无机营养物的同化；光合固定碳可在内共生体、变形细胞与宿主表皮之间高效转运，其转运速率与珊瑚中观测到的水平相当甚至更高。仙女水母共生体……