Collaborative Research: Evolutionary, biochemical and biogeochemical responses of marine cyanobacteria to warming and iron limitation interactions

海洋吸收了人类活动产生的大部分热量，海洋表面的这种变暖对重要的海洋生物群体产生了影响。海洋蓝细菌就是这样一个关键的生物群体，因为它们提供了支持几乎所有其他海洋食物网的基本碳和氮。目前，蓝细菌的生长主要受到微量营养元素铁的稀缺供应的限制，但它们对海水温度的持续升高也非常敏感。初步结果表明，气候变暖可以部分缓解铁限制对海洋蓝藻的负面影响。该项目深入研究了变暖和铁限制之间的相互作用将如何影响未来的海洋碳和氮循环，使用实验室培养实验显示蓝藻如何应对同时变化的温度和铁供应。短期反应研究和测试适应性的长期进化实验都使用了一套全面的分子生物学工具，将基因靶向蛋白质。最终目标是将这些实验的结果应用于改进定量模型，预测海洋的碳和氮循环、生物生产力和生物资源将如何应对未来气候变暖。两名研究生、一名博士后和3-4名代表性不足的本科研究人员得到了支持，研究人员还指导来自当地西班牙裔高中的暑期科学实习生。固氮蓝细菌和单细胞微蓝细菌的生理、生物化学和细菌学都受到温度的强烈影响，随着现代海洋不断变暖，它们受到强烈的选择压力。这些群体同样在长期缺铁的情况下被严格挑选出来，这种关键微量营养素的供应也随着气候的变化而变化。本项目研究了铁胁迫海洋蓝藻对温暖环境的短期适应和长期进化反应。初步数据显示，铁限制的束丝藻的铁利用效率（IUE，固定氮摩尔数.hr-1摩尔细胞Fe-1）随着5 ℃的温度升高而增加4至5倍，使得细胞能够更有效地利用稀缺的可用铁供应来生长和固定氮。这意味着变暖可以在很大程度上减轻铁限制对束毛藻的负面影响，导致在气候变暖的情况下，到2100年全球固氮量增加22%。该项目旨在揭示在此铁限制/热IUE效应中涉及的细胞生化机制，在一个为期四年的实验进化研究的固氮生物Trichodesmium和Crocosphaera和picocyanobacteria Synechococcus和Prochlorococcus，在多变量选择矩阵的温度和铁的可用性。本研究的目的是：（1）评估这四个主要蓝藻类群的适应性、IUE和生理学对铁限制和变暖相互作用的长期适应性反应：（2）利用基因组学、转录组学和定量蛋白质组学结合“金属蛋白质组学”测定关键蛋白质中铁含量，确定铁/变暖相互作用对IUE的惊人影响背后的分子和生化机制; 3）比较和对比关键蓝藻类群对铁限制和变暖的驯化和适应反应，以及4）使用已发表的生物地球化学建模方法整合结果，以评估海洋生产力和固氮的全球后果。 该项目为海洋中一些最重要的光合自养功能群体在快速变化的未来海洋环境中对铁和变暖共同压力的适应提供了一种机械和预测性的理解。该奖项反映了NSF的法定使命，并被认为值得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来支持。

The oceans absorb much of the heat generated by human activities, and this warming of the surface ocean has consequences for important groups of marine organisms. Marine cyanobacteria are one such key group of organisms, since they supply much of the essential carbon and nitrogen that supports nearly all the rest of the marine food web. Currently, the growth of cyanobacteria is mostly constrained by scarce supplies of the micronutrient element iron, but they are also very sensitive to the ongoing increases in seawater temperature. Preliminary results suggest that warming could partly mitigate the negative effects of iron limitation on marine cyanobacteria. This project examines in depth how these interactions between warming and iron limitation will affect the future ocean carbon and nitrogen cycles, using laboratory culture experiments showing how cyanobacteria respond to simultaneously changing temperature and iron supplies. Both short-term response studies and long-term evolutionary experiments testing for adaptation use a comprehensive set of molecular biology tools targeting genes to proteins. The final goal is to apply the results of these experiments to improve quantitative models predicting how the ocean's carbon and nitrogen cycles, biological productivity, and living resources will respond to a warming future climate. Two graduate students, a postdoc and 3-4 underrepresented undergraduate researchers are supported, and the investigators also mentor summer science interns from largely Hispanic local high schools. The physiology, biochemistry and biogeography of nitrogen-fixing cyanobacteria and unicellular picocyanobacteria are strongly influenced by temperature, subjecting them to intense selective pressure as the modern ocean steadily warms up. These groups have likewise been rigorously selected under chronic iron (Fe) scarcity, and the availability of this crucial micronutrient is also changing with a shifting climate. This project examines short-term acclimation and long-term evolutionary responses of Fe-stressed marine cyanobacteria to a warmer environment. Preliminary data show that Iron Use Efficiencies (IUE, mols N fixed.hr-1 mol cellular Fe-1) of Fe-limited Trichodesmium increase 4 to 5-fold with a 5oC temperature increase, allowing the cells to much more efficiently leverage scarce available Fe supplies to grow and fix nitrogen. This means that warming can to a large degree mitigate the negative effects of Fe limitation on Trichodesmium, resulting in a modelled 22% increase in global nitrogen fixation by 2100 in a warmer climate. This project aims to uncover the cellular biochemical mechanisms involved in this Fe-limitation/thermal IUE effect in a four-year experimental evolution study of the diazotrophs Trichodesmium and Crocosphaera and the picocyanobacteria Synechococcus and Prochlorococcus, under a multi-variate selection matrix of temperature and Fe availability. The objectives are to 1) Assess the long-term adaptive responses of fitness, IUE and physiology to Fe limitation and warming interactions in these four major cyanobacterial groups; 2) Determine the molecular and biochemical mechanisms behind the surprising Fe/warming interactive effect on IUE using genomics, transcriptomics and quantitative proteomics coupled with 'metalloproteomics' determinations of Fe content in critical proteins; 3) Compare and contrast acclimation and adaptation responses to Fe limitation and warming in key cyanobacteria taxa, and 4) Integrate results using a published biogeochemical modeling approach to assess global consequences for marine productivity and nitrogen fixation. This project offers a mechanistic and predictive understanding of adaptation to Fe and warming co-stressors in a rapidly changing future ocean environment for some of the most important photoautotrophic functional groups in the ocean.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.