Evolution of Oxygenic Photosynthesis as Preserved in Melainabacterial Genomes from Lake Vanda, Antarctica

大约24亿年前，在蓝细菌进化出通过光合作用（产氧光合作用）产生氧气的能力后，大气中的氧气突然上升。这一变化永久地改变了地球上生命的未来，但人们对导致这一变化的进化过程知之甚少。Melainabacteria于2013年首次被发现，是第一组能够进行产氧光合作用的生物的近亲。 该项目将利用来自南极洲冰封湖泊万达湖微生物垫的宏基因组的现有数据，此前已确定了许多Melainabacteria的序列。 根据这些遗传信息，该项目旨在评估这些Melainabacteria的代谢能力，并确定其潜在的生态作用。 该项目还将评估蓝细菌和Melainabacteria以及密切相关的生物体之间的进化关系，这将有助于进一步了解导致地球上氧光合作用的进化路径。 该项目将侧重于从Melainabacteria和Sericytochromatia的基因组数据中提取进化信息，这些基因组最近被描述为与蓝细菌密切相关但基础的群体。这些群体中的新成员的表征，从南极洲万达湖的样本，将提供深入了解的路径和过程中所涉及的含氧光合作用的演变。该研究将侧重于评估Melainabacteri的代谢能力，推导Melainabacteria和Cyanobacteria之间的进化关系，并重建导致产氧光合作用的潜在进化途径。 该项目将重点关注12个宏基因组，研究人员希望获得数据集中至少8种最丰富的Melainabacteria的基因组。将注释黑细菌箱并构建初步代谢途径。该项目将利用整个细菌域的标记基因的全长序列，特别关注产氧或缺氧光养生物的分类群，并使用标记基因，以建立一个有根的“主干”树。来自宏基因组的不完整或短序列将使用进化放置算法添加到树中。研究人员还将使用贝叶斯框架构建相应的系统发育树，并比较它们的拓扑结构。 通过这样做，该项目旨在提高对光合作用演变的理解，光合作用导致地球表面化学发生了最重大的变化。具体来说，他们将记录一个显着更广泛的代谢多样性内的Melainabacteria比以前已经确定，获得显着的见解，他们的代谢进化，他们与蓝藻的进化关系，以及进化步骤导致的起源产氧光合作用。这项研究将对限制产氧光合作用起源中的关键进化过程产生总体影响。这将为未来的研究提供基础，指出在基因组记录的进化的产氧光合作用可能会被保存。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

Atmospheric oxygen rose suddenly approximately 2.4 billion years ago after Cyanobacteria evolved the ability to produce oxygen through photosynthesis (oxygenic photosynthesis). This change permanently altered the future of life on Earth, yet little is known about the evolutionary processes leading to it. The Melainabacteria were first discovered in 2013 and are closely related non-photosynthetic relatives of the first group of organisms capable of oxygenic photosynthesis. This project will utilize existing data on metagenomes from microbial mats in Lake Vanda, an ice-covered lake in Antarctica where many sequences of Melainabacteria have been previously identified. From this genetic information, the project aims to assess the metabolic capabilities of these Melainabacteria and identify their potential ecological roles. The project will additionally evaluate the evolutionary relationships among the Cyanobacteria and Melainabacteria and closely related organisms that will allow an advancement in understanding of the evolutionary path that lead to oxygenic photosynthesis on Earth. The project will focus on extracting evolutionary information from the genomic data of Melainabacteria and Sericytochromatia, recently-described groups closely related to but basal to the Cyanobacteria. The characterization of novel members of these groups in samples from Lake Vanda, Antarctica, will provide insights into the path and processes involved in the evolution of oxygenic photosynthesis. The research will focus on assessing the metabolic capabilities of Melainabacteri, deriving the evolutionary relationships among Melainabacteria and Cyanobacteria and reconstructing potential evolutionary pathways leading to oxygenic photosynthesis. The project will focus on 12 metagenomes where the researchers expect to obtain genomes for at least the eight most abundant Melainabacteria in the dataset. Melainabacteria bins will be annotated and preliminary metabolic pathways will be constructed. The project will utilize full-length sequences of marker genes from across the bacterial domain with a particular focus on taxa that are oxygenic or anoxygenic phototrophs and use the marker genes, to build a rooted "backbone" tree. Incomplete or short sequences from the metagenomes will be added to the tree using the Evolutionary Placement Algorithm. The researchers will also build a corresponding phylogenetic tree using a Bayesian framework and compare their topologies. By doing so, the project aims to improve the understanding of the evolution of oxygenic photosynthesis, which caused the most significant change in Earth's surface chemistry. Specifically, they will document a significantly broader metabolic diversity within the Melainabacteria than has been previously identified, gain significant insights into their metabolic evolution, their evolutionary relationships with the Cyanobacteria, and the evolutionary steps leading to the origin of oxygenic photosynthesis. This research will have the overall effect of constraining key evolutionary processes in the origin of oxygenic photosynthesis. It will provide the foundation for future studies by indicating where a genomic record of the evolution of oxygenic photosynthesis may be preserved. Results will also be shared with middle school children through the development of scientific lesson plans in collaboration with teachers.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.