Dissertation Enhancement: Investigating Chloroflexi mats at a Japanese Hot Spring as a Model for Anoxygenic Stromatolites

虽然我们通常认为地球上的生命是复杂的多细胞生物，如植物和动物，但这些生物只是在最近才进化出来的，在地球过去的6亿年里？45亿年的历史。早些时候，地球上的所有生命都是微生物，由细菌和藻类等有机体组成。虽然这些生物看起来很简单，但它们是生物学中一些最重要的发明的来源，包括产氧光合作用？吸收水、阳光和二氧化碳并产生糖和氧气的能力。虽然这一过程发生在今天的植物中，但它首先是由一组称为蓝细菌的生物体发明的。光合作用产生氧气的蓝藻如何彻底改变了地球？地球的表面通过产生臭氧层，为有氧呼吸提供氧气，并允许氧气在岩石的化学风化中发挥作用而起作用。这种变化发生在大约23亿年前。不是吗？然而，我们并不清楚蓝细菌是在这个时候进化并发明了产氧光合作用，还是在地球历史上更早的时候。由于单个细菌不会留下好的化石，因此寻找它们何时进化的最佳方法之一是观察古代岩石中保存的微生物垫。该奖项支持美国研究生刘易斯沃德的博士论文研究，以研究日本温泉中形成的微生物垫，其中类似的微生物垫今天正在由蓝细菌和Chloroflexi形成，这是一组进行光合作用但不释放氧气的细菌。通过研究这两种类型的垫，并了解它们的不同之处，可以确定哪些微生物垫的特征保存在岩石记录中，并可用于区分哪组生物产生它们。通过将这些特征与整个岩石记录中保存的微生物垫进行比较，我们可以更好地了解蓝藻、光合作用和氧气的历史，进而了解地球上生命的起源。这项研究将与日本东京都立大学的环境微生物群落专家Shawn McGlynn教授合作进行。叠层石是分层的、增生的沉积结构，通常由微生物与沉积物相互作用形成。他的犯罪记录可以追溯到3. 50亿年前，它们是地球上最早的生命证据之一。虽然类似的结构可能会在没有生物学的情况下形成，但对现代类似物的广泛研究为鉴定许多古老基质的生物原性提供了可靠的标准。已知的现代叠层石类似物是由产氧蓝细菌形成的，这导致将古叠层石解释为进行产氧光合作用的蓝细菌存在的指示物。然而，独立的地质代用指标表明，蓝藻和氧气出现相对较晚，更接近氧气的上升约。2. 35 Ga.由于蓝细菌是从无氧祖先进化而来的，因此可以想象早期的基质层是由无氧光养生物形成的，但我们对这种情况是否以及如何发生的了解很少。为了解决这个难题，我们建议开发和研究一个模式叠层石形成系统组成的Chloroflexi-一门的facultimate好氧丝状细菌能够缺氧光合异养。为了促进这项工作，该奖项支持与东京都立大学的研究人员合作，他们是世界上最重要的专家之一，在Chloroflexi的分离，培养和生理研究方面。该项目将通过在日本Nakabusa Onsen温泉获得天然Chloroflexi垫来加强。这一独特的机会将允许在纯培养物和使用天然温泉垫中使用Chloroflexi有效地开发#8232;无氧基质的模型系统。该系统将直接测试在没有光合作用的情况下是否可以形成基质层（通过将它们作为好氧异养生物生长），以及进行缺氧光养的生物是否可以形成基质层。

Although we usually think of life on Earth in terms of complex multicellular organisms like plants and animals, these have evolved only relatively recently, in the last 600 million years of Earth?s 4.5 billion year history. Earlier, all life on Earth was microbial, made up of organisms like bacteria and algae. Although these organisms look simple they are responsible for some of the most important inventions in biology, including oxygenic photosynthesis?the ability to take water, sunlight, and CO2 and to produce sugar and oxygen. While this process occurs in plants today it was first invented by a group of organisms called Cyanobacteria. The production of oxygen by photosynthetic Cyanobacteria completely changed how the Earth?s surface worked, by producing the ozone layer, providing oxygen for aerobic respiration, and allowing oxygen to play a role in chemical weathering of rocks. This change occurred about 2.3 billion years ago. It isn?t well understood, however, whether Cyanobacteria evolved and invented oxygenic photosynthesis right around this time or much earlier in Earth history. Because individual bacteria don't leave good fossils, one of the best ways of looking for when they evolved is by observing preserved microbial mats in ancient rocks. This award supports doctoral dissertation research by U.S. graduate student Lewis Ward to study microbial mats forming in hot springs in Japan, where similar microbial mats are being formed today by Cyanobacteria and Chloroflexi, a group of bacteria which performs photosynthesis but without releasing oxygen. By studying these two types of mats and seeing how they differ, it is possible to determine which features of microbial mats are preserved in the rock record and can be used to distinguish which group of organisms produced them. By comparing these features to preserved microbial mats throughout the rock record, we can better understand the history of Cyanobacteria, photosynthesis, and oxygen and, by extension, the origins of life on Earth. This research will be conducted in collaboration with Professor Shawn McGlynn, an expert on microbial communities in the environment, at Tokyo Metropolitan University in Japan.Stromatolites are layered, accretionary sedimentary structures often formed by the interaction
of microbes with sediments. With a record dating back 3. 5 billion years, they are among the
 earliest evidence for life on Earth. While similar structures may form in the absence of biology, extensive investigation of modern analogs provides robust criteria for identifying the biogenicity
 of many ancient stromatolites. Known modern stromatolite analogs are formed by oxygenic Cyanobacteria, which leads to interpretation of ancient stromatolites as indicators of the presence of Cyanobacteria performing oxygenic photosynthesis. However, independent geological proxies suggest that Cyanobacteria and oxygen appear relatively late, closer to the rise of oxygen ca. 2. 35 Ga. Because Cyanobacteria evolved from anoxygenic ancestors, it is conceivable that early stromatolites were formed by anoxygenic phototrophs, but we have a poor understanding of whether and how this would 
occur. In order to resolve this conundrum we propose to develop and study a model stromatolite-forming system composed of Chloroflexi--a phylum of facultatively aerobic filamentous bacteria capable of anoxygenic photoheterotrophy. To catalyze this work, this award supports a collaboration with researchers at Tokyo Metropolitan University who are among the foremost experts in the
world at the isolation, cultivation, and physiological study of Chloroflexi. This project will be enhanced by access to natural Chloroflexi mats at a hot spring at the Nakabusa Onsen in Japan. This unique opportunity will allow effective development of a model system for
anoxygenic stromatolites using Chloroflexi in both pure culture and using natural hot spring mats. This system will directly test whether or not stromatolites can form in the absence of photosynthesis (by growing them as aerobic heterotrophs), and if organisms performing anoxygenic phototrophy can form stromatolites.