Regulation of amino acid uptake in marine unicellular cyanobacteria: light sensing and circadian clocks.

蓝藻在世界海洋的热带和亚热带地区占主导地位，原绿球藻是开放海洋的主要光合生物，聚藻球菌在低纬度的海洋边界占主导地位。最近，人们观察到原绿球藻在吸收溶解的氨基酸方面比聚藻球菌表现出明显的昼夜周期性。这些野外观测具有重要的生态学意义。例如，在热带大西洋，原绿球藻种群在中午和黄昏后分别占浮游细菌总氨基酸摄取量的10%和40%左右，因此，在营养已经枯竭的海水中，原绿球藻种群消耗了大量有机氮，对其他浮游细菌种群施加了相当大的压力。然而，仅靠田间观察还不足以了解有机养分吸收的调节机制。为了解决这个问题，我们建议使用在受控实验室条件下生长的蓝藻培养物来研究这一过程，并测试原绿球藻对氨基酸和其他可能含有机氮化合物的摄取可能受到光和/或生物钟的调节的假设。为了做到这一点，我们将使用同位素示踪剂和流式细胞术技术的组合。将蓝藻菌株暴露在不同的光照条件下（质量、数量和周期都不同），装载同位素标记的前体分子，并对处于不同细胞周期阶段的细胞进行流动分类，以确定同位素示踪剂的细胞摄取率。该项目的研究团队将拥有独特的专业知识，结合微生物生物地球化学、流式细胞术、蓝藻分子生态学的海洋技能和植物光生物学的陆地背景技能。一切必要的基本设备都已准备就绪。

Cyanobacteria numerically dominate the tropical and subtropical regions of the world's oceans with Prochlorococcus being the dominant photosynthetic organism of the open ocean and Synechococcus dominating in oceanic boundaries at low latitudes. Recently it was observed that Prochlorococcus shows a pronounced diel (day-night) periodicity in uptake of dissolved amino acids compared to Synechococcus. These field observations have important ecological implications. For example in the tropical Atlantic Ocean the Prochlorococcus population contributes around 10% and 40% to the total bacterioplankton uptake of amino acids at midday and after dusk, respectively and therefore exerts a considerable pressure on other bacterioplankton populations by consuming a significant proportion of organic nitrogen in already nutrient-depleted oceanic waters. However, field observations alone are insufficient to understand the mechanism regulating organic nutrient uptake. To address this we propose to study this process using cyanobacterial cultures grown in controlled laboratory conditions and to test the hypothesis that the uptake of amino acids, and possibly other organic nitrogen containing compounds, by Prochlorococcus could be regulated either by light and/or a circadian clock. To do this we will use a combination of isotopic tracer and flow cytometric techniques. The cyanobacterial strains will be exposed to various light regimes (varying in quality, quantity, periodicity), loaded with isotopically-labelled precursor molecules, and the cells at various cell cycle stages will be flow sorted to determine cellular uptake rates of the isotopic tracers. The research team for this project will have a unique combination of expertise with marine skills in microbial biogeochemistry, flow cytometry, molecular ecology of cyanobacteria combined with terrestrial background skills in plant photobiology. All necessary capital equipment is available.