Data from: Worldwide exploration of the microbiome harbored by the cnidarian model, Exaiptasia pallida (Agassiz in Verrill, 1864) indicates a lack of bacterial association specificity at a lower taxonomic rank

Examination of host-microbe interactions in early diverging metazoans, such as cnidarians, is of great interest from an evolutionary perspective to understand how host-microbial consortia have evolved. To address this problem, we analyzed whether the bacterial community associated with the cosmopolitan and model sea anemone Exaiptasia pallida shows specific patterns across worldwide populations ranging from the Caribbean Sea, and the Atlantic and Pacific oceans. By comparing sequences of the V1–V3 hypervariable regions of the bacterial 16S rRNA gene, we revealed that anemones host a complex and diverse microbial community. When examined at the phylum level, bacterial diversity and abundance associated with E. pallida are broadly conserved across geographic space with samples, containing largely Proteobacteria and Bacteroides. However, the species-level makeup within these phyla differs drastically across space suggesting a high-level core microbiome with local adaptation of the constituents. Indeed, no bacterial OTU was ubiquitously found in all anemones samples. We also revealed changes in the microbial community structure after rearing anemone specimens in captivity within a period of four months. Furthermore, the variation in bacterial community assemblages across geographical locations did not correlate with the composition of microalgal Symbiodinium symbionts. Our findings contrast with the postulation that cnidarian hosts might actively select and maintain species-specific microbial communities that could have resulted from an intimate co-evolution process. The fact that E. pallida is likely an introduced species in most sampled localities suggests that this microbial turnover is a relatively rapid process. Our findings suggest that environmental settings, not host specificity, seem to dictate bacterial community structure associated with this sea anemone. More than maintaining a specific composition of bacterial species some cnidarians associate with a wide range of bacterial species as long as they provide the same physiological benefits towards the maintenance of a healthy host. The examination of the previously uncharacterized bacterial community associated with the cnidarian sea anemone model E. pallida is the first global-scale study of its kind.

从演化生物学视角解析早期分化后生动物（early diverging metazoans，如刺胞动物（cnidarians））的宿主-微生物互作，对于理解宿主-微生物群落的演化历程具有重要研究价值。为解答该科学问题，本研究针对广布性模式海葵*Exaiptasia pallida*的共生细菌群落，在加勒比海、大西洋及太平洋等全球多个采样种群中是否存在特定分布模式进行了分析。通过比对细菌16S核糖体RNA基因V1-V3高变区的测序序列，我们发现海葵体内定植着复杂多样的微生物群落。在门分类水平上，*Exaiptasia pallida*的共生细菌多样性与丰度在不同地理采样区域中整体保守，群落主要由变形菌门（Proteobacteria）和拟杆菌（Bacteroides）构成。然而，这些门类下的物种组成在不同区域间差异显著，这表明该共生菌群存在高水平的核心微生物组，但其组成成分存在局部适应性演化。事实上，所有海葵样本中并未发现普遍存在的细菌操作分类单元（Operational Taxonomic Unit，OTU）。我们还发现，海葵标本在人工繁育环境中饲养四个月后，其微生物群落结构发生了改变。此外，不同地理区域间细菌群落组成的差异，与共生微藻虫黄藻（Symbiodinium）的群落组成并无相关性。本研究结果与此前的假说相悖：此前认为刺胞动物宿主可能会主动选择并维持物种特异性的微生物群落，这一过程可能源于紧密的共演化历程。*Exaiptasia pallida*在多数采样区域中可能属于外来引入物种，这一事实表明该微生物群落的更替过程相对迅速。本研究结果表明，决定该海葵共生细菌群落结构的关键因素是环境条件，而非宿主特异性。部分刺胞动物并非维持特定的细菌物种组成，而是可与多种细菌类群共生，只要这些细菌能够为宿主健康维持提供相同的生理益处。本研究是首次针对模式海葵*Exaiptasia pallida*的未表征共生细菌群落开展的全球尺度相关研究。