Mutualistic associations with symbiotic dinoflagellates (zooxanthellae) enable invertebrate hosts to thrive in tropical waters that are shallow and oligotrophic. Giant clams can harbor multiple species of symbiotic dinoflagellates (Family: Symbiodiniaceae) from mainly three genera, Symbiodinium , Cladocopium and Durusdinium , but whether they have distinct physiological functions at the genus level in the holobiont remains unclear. As symbiotic dinoflagellates use form II ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) to fix inorganic carbon, we attempted to estimate the phototrophic potentials and thus the relative abundances of Symbiodinium , Cladocopium and Durusdinium in five organs (outer mantle, inner mantle, foot muscle, ctenidium and hepatopancreas) of the fluted giant clam Tridacna squamosa through quantitative real-time PCR (qPCR) with primers that are specific to form II RuBisCO gene sequences ( rbcII ) of each genus. Based on the transcript levels of rbcII derived from Symbiodinium ( Symb-rbcII ), Cladocopium ( Clad-rbcII ) and Durusdinium ( Duru-rbcII ), we demonstrated that the symbiont population of T. squamosa from Vietnam was dominated by Durusdinium . Furthermore, the proportion of Symb-rbcII , Clad-rbcII and Duru-rbcII , and hence the phototrophic potentials of Symbiodinium , Cladocopium and Durusdinium , varied among five organs of T. squamosa , and along the length of the outer mantle. For dinoflagellates freshly isolated from the outer mantle of T. squamosa , Symb-rbcII , Clad-rbcII and Duru-rbcII exhibited different responses to light at the transcriptional level. Importantly, these results corroborate the proposition that the association with different genera and/or species of dinoflagellates might confer distinct physiological advantages to the host clam, which differs under various environmental conditions.

中文翻译：

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使用形式 II 核酮糖-1,5-二磷酸羧化酶/加氧酶来估计 Symbiodinium、Cladocopium 和 Durusdinium 在凹槽巨蛤、Tridacna squamosa 的各个器官中的光养潜力，并评估它们与宿主分离后对光的反应

与共生甲藻（虫黄藻）的相互关联使无脊椎动物宿主能够在浅层和贫营养的热带水域中茁壮成长。巨蛤可以拥有多种共生甲藻（科：Symbiodiniaceae），主要来自共生属、枝形藻属和硬壳属三个属，但它们在全息生物中是否在属水平上具有明显的生理功能尚不清楚。由于共生鞭毛藻使用 II 型核酮糖-1,5-二磷酸羧化酶/加氧酶 (RuBisCO) 来固定无机碳，因此我们试图估计光养电位，从而估计五个器官（外地幔、内层）中 Symbiodinium 、 Cladocopium 和 Durusdinium 的相对丰度地幔、足部肌肉、通过定量实时 PCR (qPCR) 使用特异于形成每个属的 II RuBisCO 基因序列 (rbcII) 的引物，对有凹槽的巨型蛤蜊 Tridacna squamosa 的 ctenidium 和 hepatopancreas) 进行了分析。基于来自共生菌 (Symbiodinium) (Symb-rbcII)、枝角藻 (Clad-rbcII) 和 Durusdinium (Duru-rbcII) 的 rbcII 的转录水平，我们证明了来自越南的 T.squamosa 的共生体种群以 Durusdinium 为主。此外，Symb-rbcII 、Clad-rbcII 和 Duru-rbcII 的比例以及共生菌、 Cladocopium 和 Durusdinium 的光养潜力在 T. squamosa 的五个器官之间以及沿外地幔的长度变化。对于刚从 T.squamosa 外地幔中分离出来的鞭毛藻，Symb-rbcII ，Clad-rbcII 和 Duru-rbcII 在转录水平上对光表现出不同的反应。重要的是，这些结果证实了与不同属和/或甲藻物种的关联可能赋予寄主蛤不同的生理优势的命题，这在不同的环境条件下是不同的。