BACKGROUND Giant clams and scleractinian (reef-building) corals are keystone species of coral reef ecosystems. The basis of their ecological success is a complex and fine-tuned symbiotic relationship with microbes. While the effect of environmental change on the composition of the coral microbiome has been heavily studied, we know very little about the composition and sensitivity of the microbiome associated with clams. Here, we explore the influence of increasing temperature on the microbial community (bacteria and dinoflagellates from the family Symbiodiniaceae) harbored by giant clams, maintained either in isolation or exposed to other reef species. We created artificial benthic assemblages using two coral species (Pocillopora damicornis and Acropora cytherea) and one giant clam species (Tridacna maxima) and studied the microbial community in the latter using metagenomics. RESULTS Our results led to three major conclusions. First, the health status of giant clams depended on the composition of the benthic species assemblages. Second, we discovered distinct microbiotypes in the studied T. maxima population, one of which was disproportionately dominated by Vibrionaceae and directly linked to clam mortality. Third, neither the increase in water temperature nor the composition of the benthic assemblage had a significant effect on the composition of the Symbiodiniaceae and bacterial communities of T. maxima. CONCLUSIONS Altogether, our results suggest that at least three microbiotypes naturally exist in the studied clam populations, regardless of water temperature. These microbiotypes plausibly provide similar functions to the clam host via alternate molecular pathways as well as microbiotype-specific functions. This redundancy in functions among microbiotypes together with their specificities provides hope that giant clam populations can tolerate some levels of environmental variation such as increased temperature. Importantly, the composition of the benthic assemblage could make clams susceptible to infections by Vibrionaceae, especially when water temperature increases. Video abstract.

中文翻译：

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元条形码揭示了砗磲中不同的微生物类型。

背景巨蛤和造礁珊瑚是珊瑚礁生态系统的关键物种。它们的生态成功的基础是与微生物之间复杂且微调的共生关系。虽然环境变化对珊瑚微生物组组成的影响已得到深入研究，但我们对与蛤相关的微生物组的组成和敏感性知之甚少。在这里，我们探讨了温度升高对巨蛤所栖息的微生物群落（来自共生科的细菌和甲藻）的影响，这些巨蛤要么与世隔绝，要么暴露在其他珊瑚礁物种中。我们使用两种珊瑚物种（Pocillopora damicornis 和 Acropora cytherea）和一种巨蛤物种（Tridacna maxima）创建了人工底栖组合，并使用宏基因组学研究了后者的微生物群落。结果我们的结果得出了三个主要结论。首先，砗磲的健康状况取决于底栖物种组合的组成。其次，我们在所研究的巨型砗磲种群中发现了不同的微生物类型，其中一种以弧菌科为主，并且与蛤死亡率直接相关。第三，水温的升高和底栖生物群落的组成对共生藻科和大砗磲细菌群落的组成均没有显着影响。结论 总而言之，我们的结果表明，无论水温如何，所研究的蛤种群中至少自然存在三种微生物类型。这些微生物型似乎通过替代分子途径以及微生物型特异性功能为蛤宿主提供了类似的功能。微生物类型之间的功能冗余及其特异性为巨蛤种群能够耐受一定程度的环境变化（例如温度升高）带来了希望。重要的是，底栖组合的成分可能使蛤容易受到弧菌科的感染，尤其是当水温升高时。视频摘要。