NSF-BSF: The role of rhodopsin phototrophy in ocean's solar energy capture and its regulation in contrasting nutrient regimes

这是一个由国家科学基金会地球科学理事会(NSF-GEO)和以色列双国科学基金会(BSF)联合资助的项目，符合NSF和BSF谅解备忘录中的语言。该协议允许由美国和以色列调查人员参与的单一合作提案提交，并由NSF进行同行审查。在NSF功绩审查和认可NSF方案推荐奖项的成功结果之后，每个机构将为与其本国相关的预算和调查人员的比例提供资金。视紫红质光营养是自然界中最简单的光依赖代谢。自从二十多年前在海洋系统中发现视紫红质基因以来，在海洋表面的大多数微生物中都发现了视紫红质基因。这意味着，一些到达海洋的太阳能可能是通过传统的基于叶绿素的光合作用以外的新陈代谢来输送的。尽管视紫红质光营养在海洋能量通量和全球碳循环中具有潜在的重要性，但它的生态作用仍然难以捉摸。为了研究它的相关性，这个团队开发了一种分析方法来确定视紫红质中光敏色素的浓度，视紫红质是视网膜的生色团。最初的估计表明，在无机盐含量非常低的海洋区域，如地中海，视紫红质比叶绿素能够捕获更多的阳光能量。然而，在北太平洋沿岸，这些模式似乎是相反的，那里的高视紫红质合成也发生在营养丰富的上升流季节。因此，目前还不清楚哪些环境变量在推动海洋中视紫红质的合成。该项目的总体目标是了解营养物质的可获得性对代表世界海洋广大区域的系统中海洋视紫红质生产和光利用的影响。这些数据是进一步推断视紫红质在全球范围内的作用并预测其在不同气候变化情景下对海洋动力学影响的关键。该项目的更广泛的影响包括支持两名研究生的论文工作，以及本科生和未被充分代表的少数族裔高中生积极参与野外工作和实验室实验。该项目研究了营养物质的可获得性对两个海洋区域微生物视紫红质光营养的影响，这两个海洋区域代表着世界海洋的大片区域：缺磷的东地中海和上升流的北太平洋。每月的视紫红质原位定量结合后基因组学和后转录组学被用来确定不同微生物分类群和环境中基于视紫红质的光营养的季节模式。这些现场数据与海水营养丰富培养实验相辅相成，该实验将营养物质的有效性与受控环境中视紫质介导的光捕获联系起来。最后，研究从北太平洋海岸和东地中海分离的含有视紫红质的细菌的特殊生理学，可以确定来自不同海洋区域和生活方式的细菌所使用的合成调节策略。总体而言，观察性和操纵性方法的结合将提供对营养供应对视紫红质分布、合成调节和能量获得的影响的更全面和更全面的了解。该项目的科学和社会影响包括了解视紫红质营养物质可能扩大的后果，以应对气候变化压力。该奖项反映了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。

This is a project jointly funded by the National Science Foundation's Directorate of Geosciences (NSF-GEO) and the Israel Binational Science Foundation (BSF) in accord with the language in the Memorandum of Understanding between the NSF and the BSF. This Agreement allows a single collaborative proposal, involving US and Israeli investigators, to be submitted and peer-reviewed by NSF. Upon successful results of the NSF merit review and recommendation by the cognizant NSF Program of an award, each Agency funds the proportion of the budget and the investigators associated with its own country. Rhodopsin phototrophy is the simplest light-dependent metabolism in nature. Since its discovery in marine systems over two decades ago, rhodopsin genes have been found in most microorganisms of the surface ocean. This implies that some of the solar energy that reaches the ocean could be channeled by metabolisms other than conventional chlorophyll-based photosynthesis. Despite the potential importance of rhodopsin phototrophy in marine energy fluxes and the global carbon cycle, its ecological role remains elusive. To study its relevance, this team has developed an analytical method to determine the concentrations of the light-sensitive pigment in rhodopsins, the chromophore retinal. First estimates suggest that rhodopsins are able to capture more sunlight energy than chlorophylls in marine regions where inorganic nutrients are very low, such as the Mediterranean Sea. Yet, these patterns seem to be opposite in the coastal north Pacific Ocean where high rhodopsin synthesis also occurs during the high-nutrient upwelling season. Therefore, it is still unclear which environmental variables are driving rhodopsin synthesis in the ocean. The overall goal of this project is to understand the effects of nutrient availability on marine rhodopsin production and light utilization in systems representative of vast areas of the world ocean. These data are key to further extrapolate the role of rhodopsins at a global scale and to predict their impact on ocean dynamics under different climate change scenarios. Broader impacts of this project include supporting the dissertation work of two graduate students and the active participation of undergraduate and underrepresented minority high school students in fieldwork and laboratory experiments.This project studies the effects of nutrient availability on microbial rhodopsin phototrophy in two marine regions which are representative of large areas of the world ocean: the oligotrophic P-limited Eastern Mediterranean Sea and the upwelling N-limited North Pacific. Monthly In situ rhodopsin quantifications coupled with metagenomics and metatranscriptomics are being used to identify the seasonal patterns of rhodopsin- based phototrophy in different microbial taxonomic groups and environments. These field data are complemented with seawater nutrient enrichment incubation experiments, which links nutrient availability to rhodopsin-mediated light capture in a controlled setting. Finally, studying the particular physiology of rhodopsin-containing bacteria isolated from the North Pacific coast and the Eastern Mediterranean allows the synthesis regulation strategies used by bacteria from different marine regions and lifestyles to be determined. Overall, this combination of observational and manipulative approaches will provide a more complete and comprehensive understanding of the effect of nutrient supply on rhodopsin distribution, synthesis regulation and energetic gain. The scientific and societal impacts of this project include understanding the consequences of a potential expansion of rhodopsin phototrophy in response to climate change forcing.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.