Data_Sheet_3_Is It First the Egg or the Shrimp? – Diversity and Variation in Microbial Communities Colonizing Broods of the Vent Shrimp Rimicaris exoculata During Embryonic Development.PDF

Rimicaris exoculata is one of the most well-known and emblematic species of endemic vent fauna. Like many other species from these ecosystems, Rimicaris shrimps host important communities of chemosynthetic bacteria living in symbiosis with their host inside the cephalothorax and gut. For many of these symbiotic partners, the mode of transmission remains to be elucidated and the starting point of the symbiotic relationship is not yet defined, but could begin with the egg. In this study, we explored the proliferation of microbial communities on R. exoculata broods through embryonic development using a combination of NGS sequencing and microscopy approaches. Variations in abundance and diversity of egg microbial communities were analyzed in broods at different developmental stages and collected from mothers at two distinct vent fields on the Mid-Atlantic Ridge (TAG and Snake Pit). We also assessed the specificity of the egg microbiome by comparing communities developing on egg surfaces with those developing on the cuticle of pleopods, which are thought to be exposed to similar environmental conditions because the brood is held under the female’s abdomen. In terms of abundance, bacterial colonization clearly increases with both egg developmental stage and the position of the egg within the brood: those closest to the exterior having a higher bacterial coverage. Bacterial biomass increase also accompanies an increase of mineral precipitations and thus clearly relates to the degree of exposure to vent fluids. In terms of diversity, most bacterial lineages were found in all samples and were also those found in the cephalothorax of adults. However, significant variation occurs in the relative abundance of these lineages, most of this variation being explained by body surface (egg vs. pleopod), vent field, and developmental stage. The occurrence of symbiont-related lineages of Epsilonbacteraeota, Gammaproteobacteria, Zetaproteobacteria, and Mollicutes provide a basis for discussion on both the acquisition of symbionts and the potential roles of these bacterial communities during egg development.

外饰亮盲虾（Rimicaris exoculata）是热液口特有动物类群中知名度最高、最具代表性的物种之一。与该生态系统中的多数物种类似，这类盲虾的头胸部与肠道内定植着与宿主形成共生关系的化能合成细菌群落。对于多数这类共生伙伴而言，其传播途径仍有待阐明，共生关系的起始节点也尚未明确，但推测可能始于卵阶段。本研究结合下一代测序（Next Generation Sequencing, NGS）与显微成像技术，探究了外饰亮盲虾卵群在胚胎发育过程中的微生物群落增殖情况。我们分析了采自大西洋中脊（Mid-Atlantic Ridge）两处不同热液场（TAG与Snake Pit）的母体所携带的、处于不同发育阶段的卵群，解析了其卵微生物群落的丰度与多样性变化。此外，通过对比卵表面与腹肢外骨骼表面的微生物群落——由于卵群被抱持于雌虾腹部下方，二者所处环境条件相似——我们评估了卵微生物组的特异性。在丰度维度上，细菌定殖量随卵发育阶段以及卵在卵群中的位置显著升高：越靠近卵群外部的卵，其细菌覆盖度越高。细菌生物量的增加同时伴随矿物沉淀的增多，因此显然与热液流体的暴露程度呈正相关。在多样性维度上，多数细菌类群在所有样本中均有检出，且这些类群同样存在于成体的头胸部中。不过，这些类群的相对丰度存在显著差异，其中大部分差异可由体表类型（卵与腹肢）、热液场以及发育阶段来解释。ε变形菌门（Epsilonbacteraeota）、γ-变形菌纲（Gammaproteobacteria）、ζ-变形菌纲（Zetaproteobacteria）以及柔膜菌纲（Mollicutes）的共生相关类群的存在，为共生体的获取途径以及这些细菌群落在卵发育过程中的潜在功能提供了讨论基础。