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

大约24亿年前，蓝藻进化出通过光合作用产生氧气的能力后，大气中的氧气突然增加。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。黑藻杆菌于2013年首次被发现，与第一组能够进行含氧光合作用的生物的非光合亲戚关系密切。该项目将利用来自南极洲万达湖（Lake Vanda）微生物垫的现有宏基因组数据，万达湖是一个冰雪覆盖的湖泊，在那里已经发现了许多黑藻杆菌的序列。根据这些遗传信息，该项目旨在评估这些黑绿杆菌的代谢能力，并确定其潜在的生态作用。该项目还将评估蓝藻菌和黑藻菌以及密切相关的生物之间的进化关系，这将有助于了解导致地球上氧气光合作用的进化途径。该项目将侧重于从黑藻菌和丝光菌的基因组数据中提取进化信息，这是最近描述的与蓝藻菌密切相关但基础的群体。在南极洲万达湖的样本中对这些群体的新成员进行表征，将为氧气光合作用进化的路径和过程提供见解。研究将集中于评估黑藻菌的代谢能力，推导黑藻菌与蓝藻菌之间的进化关系，重建可能导致氧气光合作用的进化途径。该项目将重点关注12个宏基因组，研究人员希望在这些宏基因组中获得数据集中至少8种最丰富的黑藻菌的基因组。将对黑藻菌箱进行注释，并构建初步的代谢途径。该项目将利用来自整个细菌领域的标记基因的全长序列，特别关注有氧或无氧光养生物分类群，并使用标记基因，建立一个扎根的“骨干”树。元基因组中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，该项目旨在提高对氧光合作用演变的理解，氧光合作用导致了地球表面化学的最重大变化。具体来说，他们将记录下比以前发现的更广泛的黑藻菌代谢多样性，获得对其代谢进化、与蓝藻菌的进化关系以及导致含氧光合作用起源的进化步骤的重要见解。这项研究将对限制含氧光合作用起源的关键进化过程产生总体影响。它将为未来的研究提供基础，表明在哪里可以保存氧气光合作用进化的基因组记录。研究结果还将通过与教师合作制定科学的课程计划与中学生分享。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。

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.