Collaborative Research: Iron and phosphorus balanced limitation of nitrogen fixation in the oligotrophic ocean

合作研究：贫营养海洋固氮的铁磷平衡限制

• 批准号: 1657757
• 负责人: David Hutchins
• 金额: $ 99.83万
• 依托单位: University of Southern California
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-03-01 至 2020-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1657757&HistoricalAwards=false
• 关键词: Collaborative; Research; Iron; phosphorus; balanced; Collaborative; Research; Iron; phosphorus; balanced

Marine cyanobacteria are able to use or "fix" atmospheric nitrogen gas, and so supply much of the essential nutrient nitrogen that supports open ocean food chains. Oceanographers have usually thought that the growth of these nitrogen-fixing cyanobacteria is limited at any particular time and place by the supply of either iron, or of phosphorus. Preliminary experiments have shown, though, that these nitrogen fixers instead grow best when both iron and phosphorus are scarce at the same time. In this project, the researchers will use cellular indicators that are specific for iron and phosphorus limitation to determine how important this type of "balanced limitation" of nitrogen-fixing cyanobacteria is in controlling the productivity of ocean food chains in the tropical Atlantic Ocean. Two graduate students will be trained at the University of Southern California (USC) and Woods Hole Oceanographic Institution, as well as a postdoctoral researcher at USC. Educational outreach efforts will take place at a Los Angeles inner city high school with a student body that is over 98% Hispanic and African-American, and with underrepresented undergraduates in the USC Global Environmental Microbiology course. In addition, two Research Experiences for Undergraduates students will be supervised for summer research projects to help them learn about science career options. The researchers will investigate the biological and biogeochemical consequences of this unique balanced iron/phosphorus-limited phenotype, using both laboratory and fieldwork approaches. During the first year of this project, the nitrogen-fixing cyanobacteria will be cultured under iron and/or phosphorus limitation, followed by application of proteomics and transcriptomics to identify genes that are potential diagnostic biomarkers for iron/phosphorus balanced limitation. Preliminary work has already identified one promising candidate biomarker in one cyanobacterium, an EzrA protein domain that appears to be associated with the cell size decreases seen specifically under balanced limitation, and the researchers have identified numerous other potential candidates for similar biomarkers. During the second year, these new co-limitation biomarkers and others previously validated for iron limitation (IsiB) and phosphorus limitation (SphX) will be used to investigate balanced limitation during a research cruise transecting from relatively high-iron, low-phosphorus North Atlantic waters, to the relatively high-phosphorus, low-iron South Atlantic. This fieldwork component will survey nitrogen fixing cyanobacteria populations across this natural iron/phosphorus gradient for genetic, proteomic, and physiological indicators of balanced limitation, as well as testing their responses to iron and phosphorus manipulations in shipboard incubation experiments. The third year will be devoted to sample analysis, and publications exploring the responses of oceanic nitrogen fixers to simultaneous limitation by both iron and phosphorus.

海洋蓝细菌能够使用或“固定”大气氮气，因此提供支持开放海洋食品链的许多必需营养氮。海洋学家通常认为，这些固氮蓝细菌的生长在任何特定的时间和位置都受到铁或磷的供应受到限制。但是，初步实验表明，当铁和磷同时稀少时，这些氮固定剂相反。在该项目中，研究人员将使用针对铁和磷限制的细胞指标来确定这种类型的氮固定蓝细菌的“平衡限制”在控制热带大西洋海洋食品链的生产力方面的重要性。两名研究生将在南加州大学（USC）和Woods Hole Oceanographic Institution以及USC的博士后研究员进行培训。教育外展工作将在洛杉矶内城高中进行，其学生团体超过98％的西班牙裔和非裔美国人，并且在USC全球环境微生物学课程中代表人数不足。此外，将为夏季研究项目监督学生的两种研究经验，以帮助他们了解科学职业的选择。研究人员将使用实验室和现场工作方法研究这种独特的平衡铁/磷限制的表型的生物学和生物地球化学后果。在该项目的第一年中，将固氮蓝细菌将在铁和/或磷的限制下进行培养，然后应用蛋白质组学和转录组学来识别潜在的诊断生物标志物来对铁/磷平衡的限制。初步工作已经确定了一种有前途的候选生物标志物在一个蓝细菌中，这是一个与细胞大小有关的EZRA蛋白质结构域在平衡限制下特别降低的，研究人员已经确定了许多其他类似生物标志物的潜在候选者。在第二年，这些新的共限定生物标志物以及先前已通过铁限制（ISIB）和磷限制（SPHX）的其他共同限制生物标志物（SPHX）将用于研究从相对高的铁，低磷北大西洋水的研究期间的平衡限制，以相对高磷，低磷，低磷，低磷，低磷。该野外工作成分将调查氮固定蓝细菌种群，用于遗传，蛋白质组学和生理指标的天然铁/磷梯度的平衡限制指标，并测试其对船舶孵化实验中铁和磷操作的反应。第三年将致力于样本分析，并且出版物探讨了铁和磷的海洋氮固定器对同时限制的响应。