Most tropical reef corals live at temperatures near 27°C and pH values near 8. Conditions outside of these can stress corals and lead to bleaching, disease, and death. However, some corals can survive in marginal or extreme habitats outside of these ranges. To date there is a paucity of knowledge about the role that associated microbes may play in the acclimation of corals to such extreme habitats. Here, we explore differences in the compositional and functional profile of the microbiomes of the scleractinian coral Porites panamensis living both on and off potentially stressful shallow-water hydrothermal vents. The environment near the vents is extreme, with temperatures exceeding 80°C and pH values below 6. Coral microbiomes under stress often exhibit increased diversity, increased abundance of pathogenic bacteria, and functional profiles that shift toward pathways associated with pathogenic taxa. Samples from along a transect that crossed an arc of hydrothermal vents were sequenced for the 16S rRNA gene (V4 region). On-vent coral microbiomes were distinct from those of off-vent corals, but did not have increased alpha or beta diversity. On-vent samples had a higher relative abundance of the beneficial endosymbiont, Endozoicomonas. On- and off-vent microbiomes did not differ in overall abundance of the endolithic green alga Ostreobium, however, a single ASV, close to O. quekettii was more abundant in on-vent corals. Ostreobium can provide many of the same benefits to corals as zooxanthellae and their symbiosis is better maintained under thermal stress. Surprisingly, on-vent coral microbiomes had fewer microbial taxa that are known to be pathogenic or associated with stress than did off-vent corals. The predicted functional profiles of on-vent microbiomes revealed enrichment of pathways related to aerobic respiration, fermentation and amino acid biosynthesis, but not of virulence-related pathways. Our results suggest that P. panamensis microbiomes have acclimated to the extreme environment of the hydrothermal vent habitat rather than showing signs of stress. These results exemplify the need to focus efforts on examining the mechanisms of resilience, including symbioses with microbiota, in corals living in extreme environments in an effort to design better management strategies for reef-building corals under thermal and pH stress.

大多数热带珊瑚礁生活在温度接近 27°C 且 pH 值接近 8 的环境中。除此之外的条件会对珊瑚造成压力并导致珊瑚白化、疾病和死亡。然而，一些珊瑚可以在这些范围之外的边缘或极端栖息地中生存。迄今为止，人们对相关微生物在珊瑚适应这种极端栖息地方面可能发挥的作用知之甚少。在这里，我们探索了石珊瑚的微生物组的组成和功能特征的差异槟榔生活在潜在压力大的浅水热液喷口附近。喷口附近的环境极端恶劣，温度超过 80°C，pH 值低于 6。处于压力下的珊瑚微生物群落通常表现出多样性增加、致病细菌丰度增加以及功能特征转向与致病分类群相关的途径。沿着横过一条热液喷口弧的横断面的样本对 16S rRNA 基因（V4 区域）进行了测序。通风口珊瑚微生物群落与通风口珊瑚的微生物群落不同，但没有增加 alpha 或 beta 多样性。通风口样品中有益内共生体的相对丰度较高，内生小单胞菌. 通风口内和通风口外的微生物组在石内绿藻的总体丰度方面没有差异骨杆菌，然而，一个单一的 ASV，接近 O. quekettii 在通风口珊瑚中更为丰富。 骨杆菌可以为珊瑚提供许多与虫黄藻相同的好处，并且它们的共生在热应激下得到更好的维持。令人惊讶的是，与通风口珊瑚相比，通风口珊瑚微生物群落中已知具有致病性或与压力相关的微生物分类群更少。通风口微生物组的预测功能谱揭示了与有氧呼吸、发酵和氨基酸生物合成相关的途径的富集，但与毒力相关的途径无关。我们的结果表明巴拿马松微生物组已经适应了热液喷口栖息地的极端环境，而不是表现出压力的迹象。这些结果表明，需要集中精力研究生活在极端环境中的珊瑚的弹性机制，包括与微生物群的共生关系，以便为在热和 pH 压力下的造礁珊瑚设计更好的管理策略。