Anoxygenic Photosynthesis in Cyanobacteria

理解光合作用的进化，即利用光能将二氧化碳(CO2)转化为生物质的过程，仍然是一个悬而未决的问题。许多因素扰乱了我们追踪光合作用进化的能力：相关的观察到的化学限制在遗传信息中没有明确定义，水平基因转移(微生物之间遗传信息的转移)阻碍了系统发育方法。在缺乏特征的深度分枝微生物、强大的系统基因组框架和岩石记录中无可争议的生物特征的情况下，现存蓝藻的兼性缺氧光合作用为更好地理解和限制光合作用的进化提供了机会。在这个项目中，研究人员将对一种新出现的蓝藻模式Leptolyngbya sp.的光合作用进行表征。Hensonii菌株，从缺氧的富含硫化物的天坑中分离出来。本研究将对Leptolynbya sp.的遗传反应进行评估。Hensonii菌株对硫化物的存在(这与氧合光合作用的抑制有关)和蓝藻根据环境条件表达单一光系统的潜力有关。总而言之，这些数据将提供对蓝藻在氧气光合作用进化之前的生理学和潜在成功的洞察。这项研究将考察生命在地球地球化学循环和光合作用演化中的作用，光合作用是地球生物学中的一个突出问题。该项目将培养一名研究生和一名本科生。此外，研究小组将为市场科学开发一个演示，以在明尼苏达州双子城地区及其周围的农贸市场广泛传播研究成果。通过光营养获得光并为细胞过程提供燃料的能力可以说是地球历史上最重要的生物创新之一。然而，理解光合作用的演化仍然是地球生物学中的一个悬而未决的问题。产氧光合作用经常被认为是最重要的微生物创新，它将地球的规模从早期的减少转变为有氧的世界，最终导致复杂的生命。然而，富氧光养生物使用两个反应中心：光系统II和光系统I来进行光驱动的水的氧化，以促进初级生产力。在现有的日照环境中，低氧浓度和硫化物持续存在，一些蓝藻可以利用硫化物作为光系统I的电子供体，进行缺氧光合作用。在缺乏特征的深度分枝分离株、强大的系统发育框架和岩石记录中无可辩驳的生物特征的情况下，现存蓝藻的兼性缺氧光合作用代表了一个易于处理的系统，用于研究光合作用的进化，包括早期进化的单光系统蓝藻的可能性。拟议的研究计划将结合一系列生理学研究以及系统生物学方法--转录组和蛋白质组学--来描述一种从硫酸盐缺氧环境中分离出来的新兴蓝藻模型。以下目标将指导这项工作：1)确定缺氧光合作用所需的分子机制；2)表征硫化物在缺氧光合作用过程中对光系统II的影响；3)测定硫化物在缺氧光合作用过程中的氧化动力学；4)研究硫化物存在时碳固定的增强。这项拟议的研究将考察生命在地球地球化学循环和光合作用演化中的作用。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。

Understanding the evolution of photosynthesis, the process of using light energy to convert carbon dioxide (CO2) into biomass, remains an outstanding question. A number of factors confound our ability to trace the evolution of photosynthesis: associated observed chemical limitations are not clearly defined in genetic information and horizontal gene transfer (the transfer of genetic information between microorganisms) hinders phylogenetic approaches. In the absence of characterized deeply-branching microorganisms, a robust phylogenomic framework, and undisputed biosignatures in the rock record, facultative anoxygenic photosynthesis in extant cyanobacteria represents an opportunity to better understand and constrain the evolution of photosynthesis. In this project, the investigator will characterize photosynthesis in an emerging model cyanobacterium, Leptolyngbya sp. strain hensonii, isolated from an anoxic, sulfide-rich sinkhole. This research will evaluate the genetic response of Leptolyngbya sp. strain hensonii to the presence of sulfide (which has been linked to inhibition of oxygenic photosynthesis) and the potential for a cyanobacterium to express a single photosystem based on environmental conditions. Collectively, the data will provide insight into the physiology and potential success of cyanobacteria prior to the evolution of oxygenic photosynthesis. The study will examine the role of life in the transformation and evolution of Earth's geochemical cycles and the evolution of photosynthesis, which is an outstanding question in geobiology. The project will train a graduate student and an undergraduate student. In addition, the research team will develop a demonstration for Market Science to broadly disseminate findings at Farmers' Markets in and around the Twin Cities area of Minnesota.The ability to harvest light and fuel cellular processes through phototrophy is arguably one the most important biological innovations in Earth history. Yet, understanding the evolution of photosynthesis remains an outstanding question in geobiology. Oxygenic photosynthesis is often cited as the most important microbial innovation having tipped the scale from a reducing early Earth to an oxygenated world that eventually lead to complex life. However, oxygenic phototrophs use two reaction centers: Photosystem II and Photosystem I for light-driven oxidation of water to fuel primary productivity. In extant sunlit environments where low oxygen concentrations and sulfide persist, some cyanobacteria can use sulfide as the electron donor to photosystem I, performing anoxygenic photosynthesis. In the absence of characterized deeply-branching isolates, a robust phylogenomic framework, and irrefutable biosignatures in the rock record, facultative anoxygenic photosynthesis in extant cyanobacteria represents a tractable system for examining the evolution of photosynthesis including the potential for an early evolving one-photosystem cyanobacterium. The proposed research plan will integrate a set of physiological studies coupled with systems biology approaches—transcriptomics and proteomics—to characterize an emerging model cyanobacterium isolated from a sulfidic, anoxic environment. The following objectives will guide this work: 1) define the molecular machinery necessary for anoxygenic photosynthesis; 2) characterize the effects of sulfide on photosystem II during anoxygenic photosynthesis; 3) determine oxidation kinetics of sulfide during anoxygenic photosynthesis; 4) examine the enhancement of carbon fixation in the presence of sulfide. The proposed research will examine the role of life in the transformation and evolution of Earth's geochemical cycles and the evolution of photosynthesis.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.