Postdoctoral Fellowship: OCE-PRF: Do diatoms use proton-pumping rhodopsins as an alternative energy source under high light

博士后奖学金：OCE-PRF：硅藻在高光下使用质子泵视紫红质作为替代能源

• 批准号: 2307229
• 负责人: Brittany Zepernick
• 金额: $ 29.82万
• 依托单位: University of North Carolina at Chapel Hill
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-12-01 至 2025-11-30
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2307229&HistoricalAwards=false
• 关键词: Postdoctoral; Fellowship; OCE; PRF; Do

We are well aware that algae living in the global oceans play a critical role in the cycling of carbon and climate. Notably, algae called diatoms are responsible for a large proportion of carbon uptake and sequestration in the world’s oceans. Due to this, diatoms are considered “first responders” to climate change. More specifically they offset increasing carbon dioxide in the Earth’s atmosphere by transferring it to the deep ocean. However, climate change is altering the oceans and the ability of diatoms to survive. Specifically, climate change is increasing the intensity of light in the oceans via a process called “shoaling” and decreasing the amount of iron. Both conditions negatively affect diatoms by hindering photosynthesis. Recently it was discovered some diatoms possess proton pumping rhodopsins, which may serve as an alternative means to generate energy when photosynthesis is not feasible (for example during low iron and high light conditions). Yet while previous work found diatoms increase the use of proton pumping rhodopsins when they are iron-limited, it did not investigate the other condition which hinders photosynthesis, namely high light. The purpose of this project is to investigate how diatom proton pumping rhodopsins function under low iron and high light stress. Broadly, this work will extend to other algae and bacteria which use proton pumping rhodopsins to harvest light and generate energy. In turn, this work will provide insight on how diatoms will respond to the future oceans and how carbon cycling may be altered. This project will broaden diversity and engagement within the field of oceans science through various classroom and community outreach activities in addition to mentoring opportunities. Cumulatively, this work will enhance the ability to model and predict future climate scenarios across the global oceans. Diatoms are phototrophic protists responsible for ~40% of global marine primary production and organic carbon export. Recently, it was discovered some diatoms possess proton-pumping rhodopsins (PPRs), light-driven proton pumps that may contribute as much to cellular energy generation as photosynthesis. Prior data suggests PPR contributions to energy generation increase under iron-limitation, implying diatoms elicit a “phototrophic trade-off” by increasing PPR phototrophy when conditions for photosynthesis are unfavorable. While photosynthesis may become light-saturated at low light levels (e.g., 60-80mol photons m-2 s-1 in polar diatoms), based on photocyclic turnover rates, PPRs become light saturated at ~2000 mol photons m-2 s-1, suggesting PPRs are favored under high light. Yet, diatom PPR phototrophy has not been studied under high irradiance. Further, photosynthesis in iron-limited cells tends to become inhibited at lower light compared to iron-replete cells. This is of pertinence as ocean stratification serves to increase irradiance, and ~30% of marine primary production occurs under iron limitation. This proposal will investigate how high light levels + iron limitation alter the two major phototrophic strategies (and competitive fitness) of a diverse group of marine diatoms via a combination of in vitro laboratory analyses and biochemical assays. Photosynthetic phototrophy will be assessed via 14C isotope tracing, FIRe fluorometry, and photopigment extractions (HPLC). PPR phototrophy will be assessed via intracellular pH and calculations using retinal quantifications (LC-MS/MS). Ecological insights on how the presence vs. absence of PPRs alters diatom competitive fitness under high light + iron limitation will be assessed, with competitive fitness determined via growth dynamics and transcriptomics. Cumulatively, this work will characterize the present role of PPRs in diatom phototrophy and provide insight on the role of PPRs in a more stratified (and variable light) future. Classroom and community STEM engagement will be facilitated with local schools and the Morehead Planetarium and Science Center of UNC Chapel Hill. Broadly, this project will offer novel insights regarding the influence of iron limitation + irradiance on PPR phototrophy and competitive fitness, a strategy common to many marine protists. In addition to the biogeochemical and ecological implications of this project, our study will provide transformative insights into diatom evolution under changing ocean conditions.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.

我们清楚地知道，生活在全球海洋中的藻类在碳和气候循环中发挥着至关重要的作用。值得注意的是，被称为硅藻的藻类负责世界海洋中很大一部分碳的吸收和封存。因此，硅藻被认为是气候变化的“第一反应者”。更具体地说，它们通过将地球大气中不断增加的二氧化碳转移到深海来抵消它。然而，气候变化正在改变海洋和硅藻的生存能力。具体来说，气候变化通过一种称为“浅滩”的过程增加了海洋中的光强度，并减少了铁的含量。这两种情况都会阻碍光合作用，从而对硅藻产生负面影响。最近发现一些硅藻具有质子泵视紫红质，当光合作用不可行时（例如在低铁和高光条件下），它可以作为产生能量的替代方法。然而，虽然之前的研究发现硅藻在铁受限时会增加质子泵视紫红质的使用，但它没有研究阻碍光合作用的其他条件，即强光。该项目的目的是研究硅藻质子泵视紫红质在低铁和高光胁迫下如何发挥作用。从广义上讲，这项工作将扩展到其他藻类和细菌，它们利用质子泵视紫红质来收集光并产生能量。反过来，这项工作将提供有关硅藻如何应对未来海洋以及碳循环如何改变的见解。除了指导机会之外，该项目还将通过各种课堂和社区外展活动扩大海洋科学领域的多样性和参与度。总的来说，这项工作将增强模拟和预测全球海洋未来气候情景的能力。硅藻是光养原生生物，约占全球海洋初级生产和有机碳出口的 40%。最近，人们发现一些硅藻具有质子泵视紫红质（PPR），即光驱动的质子泵，其对细胞能量产生的贡献可能与光合作用一样大。先前的数据表明，在铁限制下，PPR 对能量产生的贡献增加，这意味着当光合作用条件不利时，硅藻通过增加 PPR 光养来引发“光养权衡”。虽然光合作用在低光水平下可能会达到光饱和（例如，极性硅藻中的 60-80μmol 光子 m-2 s-1），但根据光循环周转率，PPR 在约 2000 μmol 光子 m-2 s-1 时会达到光饱和，这表明 PPR 在高光下更受青睐。然而，硅藻PPR光养作用尚未在高辐照度下进行研究。此外，与铁充足的细胞相比，铁有限的细胞中的光合作用在较低的光照下往往会受到抑制。这是相关的，因为海洋分层会增加辐照度，并且约 30% 的海洋初级生产力发生在铁限制下。该提案将通过体外实验室分析和生化测定相结合，研究高光水平+铁限制如何改变不同海洋硅藻类群的两种主要光养策略（和竞争适应性）。光合光养作用将通过 14C 同位素示踪、FIRe 荧光测定法和感光色素提取 (HPLC) 进行评估。 PPR 光养作用将通过细胞内 pH 值进行评估，并使用视网膜定量 (LC-MS/MS) 进行计算。将评估关于 PPR 的存在与不存在如何改变高光 + 铁限制下硅藻竞争适应性的生态见解，并通过生长动力学和转录组学确定竞争适应性。总之，这项工作将描述 PPR 在硅藻光养中的当前作用，并提供有关 PPR 在更加分层（和可变光）的未来中的作用的见解。当地学校、莫尔黑德天文馆和北卡罗来纳大学教堂山科学中心将促进课堂和社区 STEM 参与。总的来说，该项目将提供关于铁限制+辐照度对 PPR 光养和竞争适应性的影响的新颖见解，这是许多海洋原生生物常见的策略。除了该项目的生物地球化学和生态影响外，我们的研究还将为不断变化的海洋条件下的硅藻进化提供变革性的见解。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。