Bacterial Population Structure: Evaluating Gene Flow in the Symbionts of Deep-Sea Mussels \(Genus Bathymodiolus\)

最近的证据表明，微生物种群在空间和化学碎片化的栖息地分布并不普遍，而是表现出地理结构。异质性环境限制了种群间的基因流动，从而促进了遗传分化、局部适应和物种形成。由于地形特征、深海洋流和喷口流体化学性质的变化，热液喷口呈片状分布。虽然化学合成细菌与其无脊椎宿主之间的联系为深海热液喷口的大型底栖动物生产提供了依据，但对共生体遗传变异的分布以及细菌种群结构如何影响喷口的生态相互作用和共生体的演变几乎一无所知。 本研究项目将通过检查遗传结构沿着东太平洋海隆（EPR），大西洋中脊（MAR）和劳弧后盆地（Lau）内的贻贝栖息快速，缓慢和不连续的扩散中心的硫自养和甲烷营养内共生体的种群的基因流模型进行测试。Bathymodiolus贻贝几乎在所有热液喷口都有发现，并且很可能在每一代都从环境中获得共生体，使其成为评估细菌内共生体地理结构的模型系统。将研究来自3个脊、每个脊5个喷口场的共生体和每个喷口场2-4个地点的贻贝。对于这两种类型的共生体，4个DNA标记（16 s rRNA，ITS，ftsZ，以及pmoA或soxY的甲烷营养菌和硫自养菌，分别）将测序从20-30贻贝个体每个站点。在数据分析中，将采用群体遗传学、联合学和地理学方法。影响细菌内共生体种群结构的机制对深海热液喷口的微生物群落学、多样性以及生命的起源、进化和生态具有重要意义。 这项研究将产生第一个高分辨率的基因流之间的环境传播的内共生种群的检查。 对热液喷口区进行比较将提供关于细菌物种历史地理和扩散障碍的宝贵资料。 这些发现将允许更广泛的推论，关于深海洋流如何影响扩散和化能自养群落的进化。 此外，由于热液喷口是早期地球和地外环境的类似物，这项研究的结果将对真核细胞器的起源以及极端生物群落中微生物的生态和进化产生影响。注释的基因序列将保存在GenBank中，并通过网站（www.endosymbiont.org）公开访问，研究人员使用该网站向科学界和公众提供有关内共生的信息。 研究人员还为公众提供科学主题的研讨会，包括微生物共生和多样性，化学合成和地球上的生命等。 本科生，研究生和博士后研究员将有充分的机会参与这些基因序列的分析，无论是通过他们的研究，并通过纳入大学课程。

Recent evidence suggests that microbial populations in spatially and chemically fragmented habitats are not distributed ubiquitously, but rather exhibit geographic structure. Heterogeneous environments restrict gene flow among populations, which promotes genetic differentiation, local adaptation, and speciation. Hydrothermal vents are distributed in a patchy array due to topographic features, deep ocean currents, and variations in vent fluid chemistry. Though associations between chemosynthetic bacteria and their invertebrate hosts provide the basis for macrofaunal production at deep-sea hydrothermal vents, almost nothing is known about the distribution of genetic variation in the symbionts and how population structure of bacteria affects ecological interactions and the evolution of symbioses at vents. This research project will test models of gene flow for populations of thioautotrophic and methanotrophic endosymbionts of mussels inhabiting fast-, slow-, and discontinuous spreading centers by examining genetic structure along the East Pacific Rise (EPR), Mid-Atlantic Ridge (MAR) and within the Lau Back-arc Basin (Lau), respectively. Bathymodiolus mussels are found at nearly all hydrothermal vent sites and most likely acquire their symbionts from the environment in each generation, making them model systems for evaluating geographic structure of bacterial endosymbionts. Symbionts from 3 ridges, 5 vent fields per ridge, and mussels from 2-4 sites per vent field will be studied. For both types of symbiont, 4 DNA markers (16s rRNA, ITS, ftsZ, and either pmoA or soxY for the methanotroph and thioautotroph, respectively) will be sequenced from 20-30 mussel individuals per site. Population genetic, coalescent, and phylogeographic approaches will be employed in the data analyses. Mechanisms that affect the population structure of bacterial endosymbionts have important implications for microbial biogeography, diversity, and the origin, evolution, and ecology of life at deep-sea hydrothermal vents. This research will yield the first high-resolution examination of gene flow among environmentally transmitted endosymbiont populations. Comparisons between hydrothermal vent fields will provide valuable information on the historical biogeography and barriers to dispersal for bacterial species. These findings will allow broader inferences regarding how deep ocean currents influence dispersal and the evolution of chemoautotrophic communities. Further, because hydrothermal vents serve as analogs to early Earth as well as extraterrestrial environments, results from this research will have implications for the origin of eukaryotic cell organelles and the ecology and evolution of microbes in extreme biomes. Annotated gene sequences will be deposited in GenBank and made publicly accessible through a website (www.endosymbiont.org) that the investigators use to present information on endosymbiosis to the scientific and public community. The investigators also give seminars designed for the general public on scientific topics, including microbial symbiosis and diversity, chemosynthesis and life on this planet and others. Undergraduates, graduate students, and postdoctoral fellows will have ample opportunity to participate in analyses of these gene sequences, both through their research and through inclusion in university courses.