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

大约24亿年前，在蓝藻通过光合作用(产氧光合作用)进化出产生氧气的能力后，大气中的氧气突然上升。这种变化永久性地改变了地球上生命的未来，但人们对导致这种变化的进化过程知之甚少。黑细菌于2013年首次被发现，它们与第一批能够进行氧合光合作用的生物有着密切的非光合作用亲缘关系。该项目将利用来自万达湖微生物垫的现有数据，万达湖是南极洲的一个冰盖湖泊，此前已在那里发现了许多Melainabacteria序列。根据这些遗传信息，该项目旨在评估这些黑细菌的新陈代谢能力，并确定它们潜在的生态作用。该项目还将评估蓝藻和黑藻以及与之密切相关的生物之间的进化关系，这将促进对导致地球上氧气光合作用的进化路径的理解。该项目将专注于从黑细菌和丝色细菌的基因组数据中提取进化信息，这两个群体最近被描述为与蓝藻密切相关但基础的群体。对南极洲万达湖样品中这些新成员的表征，将为我们深入了解氧气光合作用的进化路径和过程提供线索。这项研究将集中于评估黑藻的代谢能力，推导黑藻和蓝藻之间的进化关系，并重建导致氧合光合作用的潜在进化途径。该项目将集中在12个元基因组上，研究人员希望在这些基因组中至少获得数据集中最丰富的8个黑藻的基因组。将对黑线杆菌垃圾箱进行注释，并构建初步的代谢途径。该项目将利用来自细菌领域的全长标记基因序列，特别关注产氧或产氧光养生物的分类群，并使用标记基因来构建有根的“主干”树。来自元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，该项目旨在提高对氧气光合作用进化的理解，氧气光合作用导致了地球表面化学最重大的变化。具体地说，他们将记录下黑藻中比以前发现的更广泛的代谢多样性，获得对它们的代谢进化、它们与蓝藻的进化关系以及导致充氧光合作用起源的进化步骤的重要见解。这项研究将对限制氧气光合作用起源的关键进化过程产生整体影响。它将为未来的研究提供基础，因为它表明了氧合光合作用进化的基因组记录可能被保存在哪里。结果还将通过与教师合作制定科学的教案与中学生分享。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.