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

这是一个由美国国家科学基金会地球科学理事会（NSF- geo）和以色列两国科学基金会（BSF）根据国家科学基金会和BSF之间的谅解备忘录共同资助的项目。该协议允许美国和以色列研究人员提交一份单一的合作提案，并由NSF进行同行评审。在国家科学基金会的评审结果和认可的国家科学基金会项目的推荐下，每个机构资助预算的比例和与自己国家有关的调查人员。视紫红质是自然界最简单的光依赖性代谢。自从二十多年前在海洋系统中被发现以来，在海洋表面的大多数微生物中都发现了视紫红质基因。这意味着到达海洋的一些太阳能可以通过代谢而不是传统的基于叶绿素的光合作用来引导。尽管视紫红质在海洋能量通量和全球碳循环中具有潜在的重要性，但其生态作用仍然难以捉摸。为了研究其相关性，该团队开发了一种分析方法来确定视紫红质（即发色团视网膜）中光敏色素的浓度。最初的估计表明，在地中海等无机营养物质非常少的海洋地区，视紫红质比叶绿素能够捕获更多的阳光能量。然而，这些模式似乎在北太平洋沿岸相反，在高营养上升流季节也发生高视紫红质合成。因此，目前尚不清楚哪些环境变量驱动了海洋中的视紫红质合成。该项目的总体目标是了解在具有代表性的世界海洋广大地区的系统中，营养物可得性对海洋视紫红质生产和光利用的影响。这些数据对于进一步推断紫红质在全球范围内的作用以及预测其在不同气候变化情景下对海洋动力学的影响至关重要。这个项目更广泛的影响包括支持两名研究生的论文工作，以及本科生和少数民族高中学生积极参与实地考察和实验室实验。本项目研究了两个具有代表性的海洋区域的营养物有效性对微生物紫红质光养性的影响，这两个海洋区域是贫营养化的限制磷的东地中海和上升流限制氮的北太平洋。每月原位紫红质定量结合宏基因组学和元转录组学被用于确定不同微生物分类群和环境中基于紫红质的光养的季节性模式。这些实地数据与海水营养物富集培养实验相辅相成，该实验将营养物可用性与受控环境中视紫红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紫红质细菌的特定生理，可以确定来自不同海洋区域和生活方式的细菌使用的合成调节策略。总之，这种观察和操作相结合的方法将提供更完整和全面的了解营养供应对视紫红质分布、合成调节和能量增益的影响。该项目的科学和社会影响包括了解视紫红质在应对气候变化强迫下可能扩大的后果。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。

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.