Department of Integrative Biology, Oregon State University, Corvallis, OR, United States of America.
Department of Biology, Lewis and Clark College, Portland, OR, United States of America.
PeerJ. 2022 Jul 29;10:e13796. doi: 10.7717/peerj.13796. eCollection 2022.
Many cnidarians rely on their dinoflagellate partners from the family Symbiodiniaceae for their ecological success. Symbiotic species of Symbiodiniaceae have two distinct life stages: inside the host, , and outside the host, . Several aspects of cnidarian-algal symbiosis can be understood by comparing these two life stages. Most commonly, algae in culture are used in comparative studies to represent the life stage, however, nutrition becomes a confounding variable for this comparison because algal culture media is nutrient rich, while algae are sampled from hosts maintained in oligotrophic seawater. In contrast to cultured algae, expelled algae may be a more robust representation of the state, as the host and expelled algae are in the same seawater environment, removing differences in culture media as a confounding variable. Here, we studied the physiology of algae released from the sea anemone (commonly called Aiptasia), a model system for the study of coral-algal symbiosis. In Aiptasia, algae are released in distinct pellets, referred to as egesta, and we explored its potential as an experimental system to represent Symbiodiniaceae in the state. Observation under confocal and differential interference contrast microscopy revealed that egesta contained discharged nematocysts, host tissue, and were populated by a diversity of microbes, including protists and cyanobacteria. Further experiments revealed that egesta were released at night. In addition, algae in egesta had a higher mitotic index than algae , were photosynthetically viable for at least 48 hrs after expulsion, and could competently establish symbiosis with aposymbiotic Aiptasia. We then studied the gene expression of nutrient-related genes and studied their expression using qPCR. From the genes tested, we found that algae from egesta closely mirrored gene expression profiles of algae and were dissimilar to those of cultured algae, suggesting that algae from egesta are in a nutritional environment that is similar to their counterparts. Altogether, evidence is provided that algae from Aiptasia egesta are a robust representation of Symbiodiniaceae in the state and their use in experiments can improve our understanding of cnidarian-algal symbiosis.
许多刺胞动物依靠共生的甲藻家族 Symbiodiniaceae 来获得生态成功。共生的 Symbiodiniaceae 物种有两个明显的生活阶段：在宿主内部和在宿主外部。通过比较这两个生活阶段，可以理解刺胞动物-藻类共生的几个方面。最常见的是，在比较研究中使用培养的藻类来代表 生活阶段，然而，由于藻类培养物富含营养，而从贫营养海水中维持的宿主中采样的藻类 ，营养成为了这个比较的混杂变量。与培养的藻类相比，排出的藻类可能更能代表 状态，因为宿主和排出的藻类处于相同的海水环境中，消除了培养基作为混杂变量的差异。在这里，我们研究了从海葵（通常称为海葵）中释放的藻类的生理学，海葵是珊瑚-藻类共生研究的模式系统。在海葵中，藻类以明显的颗粒形式释放，称为排出物，我们探索了它作为代表共生甲藻 状态的实验系统的潜力。共聚焦和微分干涉对比显微镜观察显示，排出物包含排出的刺丝囊、宿主组织，并且由多种微生物组成，包括原生动物和蓝细菌。进一步的实验表明，排出物是在夜间释放的。此外，排出物中的藻类比藻类 具有更高的有丝分裂指数，在排出后至少 48 小时内仍具有光合作用能力，并且能够与无共生的海葵建立共生关系。然后，我们研究了与营养相关的基因的表达，并使用 qPCR 研究了它们的表达。在所测试的基因中，我们发现排出物中的藻类与藻类 的基因表达谱非常相似，而与培养的藻类不同，这表明排出物中的藻类处于与它们的 对应物相似的营养环境中。总之，有证据表明，来自海葵排出物的藻类是共生甲藻 状态的有力代表，它们在实验中的使用可以提高我们对刺胞动物-藻类共生关系的理解。
