Bone-eating worms of the genus Osedax (Annelida, Siboglinidae) form unique holobionts (functional entity comprising host and associated microbiota), highly adapted to inhabit bone tissue of marine vertebrates. These gutless worms have developed nutritional symbioses housing intracellular, horizontally acquired, heterotrophic bacteria hypothesised to harness nutrients from organic compounds, sequestered within the bone. Despite previous efforts, critical mechanisms mediating activity and acquisition of diverse bacterial assemblages remain unclear. Using 16S rRNA amplicon sequencing, we performed detailed taxonomic and predicted functional analyses shedding light on the microbial communities of two shallow-water Osedax species (Osedax deceptionensis and Osedax ‘mediterranea’) from contrasting habitats (Antarctic and Mediterranean Sea), in two tissue types (roots and palps). Comparative assessments between host species revealed distinct microbial assemblages whilst, within host species and body tissue, relative symbiont frequencies retained high variability. We reported relatively high abundances of microbes previously classified as primary endosymbionts, Ribotype 1 (order Oceanospirillales), and diverse likely secondary epibionts warranting further exploration as recurrent Osedax associates. Surprisingly, O. ‘mediterranea’ exhibited relatively low abundance of Oceanospirillales, but increased abundance of other potentially hydrocarbon degrading bacteria from the family Alteromonadaceae. We hypothesise the presence of functionally similar, non-Oceanospirillales primary endosymbionts within O. ‘mediterranea’. Functional metagenomic profiling (using 16S rRNA sequences) predicted broad metabolic capabilities, encompassing relatively large abundances of genes associated with amino acid metabolism. Comparative analyses between host body tissue communities highlighted several genes potentially providing critical functions to the Osedax host or that confer adaptations for intracellular life, housed within bone embedded host root tissues.

中文翻译：

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来自南极和地中海浅水食骨蠕虫的微生物见解

Osedax 属的食骨蠕虫（Annelida，Siboglinidae）形成独特的全息生物（包括宿主和相关微生物群的功能实体），非常适合栖息在海洋脊椎动物的骨组织中。这些无肠蠕虫已经发展出营养共生体，容纳细胞内的、水平获得的、异养细菌，假设可以利用有机化合物中的营养物质，隔离在骨骼内。尽管之前做出了努力，但介导各种细菌组合的活动和获取的关键机制仍不清楚。使用 16S rRNA 扩增子测序，我们进行了详细的分类和预测功能分析，揭示了来自对比栖息地（南极和地中海）的两种浅水 Osedax 物种（Osedax deceptionensis 和 Osedax 'mediterranea'）的微生物群落，在两种组织类型（根和触须）中。宿主物种之间的比较评估揭示了不同的微生物组合，而在宿主物种和身体组织内，相对共生体频率保持高度可变性。我们报告了相对高丰度的微生物，以前被归类为初级内共生体、核糖体 1（海洋螺旋目）和多种可能的次级外生体，值得进一步探索作为复发性 Osedax 关联。令人惊讶的是，O. 'mediterranea' 显示出相对较低的海洋螺旋藻丰度，但增加了来自交替单胞菌科的其他潜在碳氢化合物降解细菌的丰度。我们假设在 O. 'mediterranea' 中存在功能相似的非海洋螺旋体主要内共生体。功能宏基因组分析（使用 16S rRNA 序列）预测了广泛的代谢能力，包括与氨基酸代谢相关的大量基因。宿主身体组织群落之间的比较分析突出了几个基因，这些基因可能为 Osedax 宿主提供关键功能或赋予细胞内生命适应性，这些基因位于嵌入骨骼的宿主根组织中。