In the belly of the whale: endobionts inhabit the world's largest bacteria

线粒体和叶绿体——为真核细胞提供能量的细胞器——被认为是在20多亿年前从生活在微生物体内的共生细菌进化而来的。尽管它们有可能有助于理解真核生物的进化，但细菌宿主其他细菌的例子非常罕见。首席研究人员最近发现了一种巨大的细菌种群，它们的细胞内有密集的细菌种群。研究人员将研究与巨型细菌相关的细菌群落，确定某些细菌如何进入宿主细胞，并探索细胞内细菌与巨型宿主细胞之间的相互作用。这个系统提供了一个独特的机会来了解这种宿主细菌-细菌的共生关系。除了探索真核生物进化和微生物相互作用的基本方面外，研究人员还将为美国退伍军人学生、美国高中生和来自纳米比亚的学生提供实地和实验室经验，将学生聚集在一个新颖的交流项目中。这一国际伙伴关系不仅将帮助培训STEM领域的美国资深学生和来自代表性不足群体的高中生，而且还将通过培训学生学习基本细胞过程的尖端方法，帮助扩大撒哈拉以南非洲的研究能力。涉及原核宿主细胞和其他原核生物的内共生关系是极其罕见的，而且还没有得到很好的理解。研究人员最近发现了一群代谢活跃的巨型硫细菌细胞，Thiomargarita spp.，其中含有密集的细胞内细菌群。其中一些细菌与已知的动物内共生菌有关，但这些细胞内细菌群落的结构和生态学仍然不完整。为了更好地了解宿主细菌与细菌的共生关系，研究者们正在进行以下研究：(1)研究与Thiomargarita spp.不同种型相关的微生物群落结构；(2)确定细胞进入Thiomargarita spp.的潜在机制；(3)研究Thiomargarita spp.内生物细菌与Thiomargarita spp.细胞之间的生态生理相互作用。除了对群落组成进行表征外，还采用了一系列不同的技术，如宏基因组学、元转录组学和荧光原位杂交。此外，正在进行感染挑战实验，以阐明内生物在宿主细胞内内化的潜在机制。这项研究有可能为真核生物的进化和宿主原核生物-内共生原核生物共生基础上的相互作用提供见解。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Mitochondria and chloroplasts, the organelles that provide energy to the eukaryotic cell, are thought to have evolved more than two billion years ago from symbiotic bacteria that lived within a microbe. Despite their potential to help in the understanding of eukaryote evolution, examples of bacteria that host other bacteria are very rare. The principal investigators recently discovered a population of giant bacteria that host dense populations of bacteria within their cells. The investigators will study the community of bacteria associated with the giant bacteria, determine how certain bacteria enter the host cells, and explore the interactions among the intracellular bacteria and the giant host cell. This system provides a unique opportunity to gain an understanding of this host bacterium-bacteria symbioses. In addition to exploring basic aspects of eukaryotic evolution and microbial interactions, the investigators will provide field and laboratory experiences for U.S. military veteran students, U.S. high school students, and students from Namibia, bringing the students together in a novel exchange program. This international partnership will not only help train U.S. student veterans in STEM fields, and high school students from underrepresented groups, but also help to expand the research capabilities of sub-Saharan Africa by training students in cutting-edge approaches to studying fundamental cell processes.Endosymbiotic relationships involving prokaryotic host cells and other prokaryotes are extremely rare and not well understood. The investigators recently discovered a population of metabolically active giant sulfur bacteria cells, Thiomargarita spp., that contain dense populations of intracellular bacteria. Some of these bacteria are related to known animal endosymbionts but the structure and ecology of these intracellular bacterial communities is still incomplete. To better understand the host bacterium-bacteria symbioses, the investigators are (1) investigating the microbial community structure associated with different phylotypes of Thiomargarita spp., 2) identifying the potential mechanism(s) by which cells enter Thiomargarita spp., and 3) studying ecological and physiological interactions between the endobiont bacteria and Thiomargarita spp. In order to investigate potential interactions between host Thiomargarita spp. cells and their endobionts, as well as to characterize the community compositions, a set of diverse techniques, such as metagenomics, metatranscriptomics, and fluorescence in situ hybridization, are being employed. In addition, infection challenge experiments are being performed to elucidate the potential mechanisms by which the endobiont(s) becomes internalized within the host cell. This research has the potential to provide insights into eukaryotic evolution and the interactions that underlie the host prokaryote-endosymbiotic prokaryotes symbioses.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.