How important is prokaryotic photoheterotrophy in ecosystems of the Atlantic Ocean from 40oS to 40oN?

该提案的目的是找出光异质营养在开阔的海洋中有多重要--这是地球上最大的生态系统，对全球生物地球化学和气候具有深远的重要性。光异养原核生物利用光作为能源，但不能将二氧化碳作为唯一的碳源，因此使用环境中的有机分子来满足它们的碳需求。尽管在理解几种光异养机制方面取得了相当大的进展，但太阳辐射在海洋浮游细菌新陈代谢中的作用很难评估，尽管已经很明显，原核细胞固定二氧化碳可能只是画面的一部分。该项目建议对SAR11α蛋白细菌和原氯球藻蓝细菌因其光异质营养而在数量上主导公海的假设进行实验测试和数学建模。利用实验室和海洋巡航实验相结合的方法，将解决以下目标：(I)确定主要浮游原核生物群SAR11和原氯球藻对磷酸盐和氨基酸的吸收速率随光照强度和光谱的变化，并将这些速率与蓝藻固定二氧化碳的速率联系起来；(Ii)量化真光带内特定类群对磷和氨基酸的光增强吸收速率在中尺度上的空间和深度相关变化，将光异质营养的这些变化与北大西洋亚热带涡旋中优势种群的种群规模和组成联系起来；(3)利用光增强氨基酸吸收，比较北大西洋环流与南部环流和赤道区域的光异养速率，以确定在海洋尺度上光异养利用的意义。为了实现上述目标，我们将重点开展开放大西洋的实验工作，将同位素示踪营养生物分析与浮游细菌细胞的流式细胞术分选相结合，然后进行细胞的超灵敏放射分析，通过荧光原位杂交和纳米级二次离子质谱仪进行细胞鉴定，并通过卤素原位杂交进行原核细胞的分子鉴定。我们的首要目标是建立太阳能对开放海洋微生物世界的输入，而不是用于固定二氧化碳的输入。

The aim of the proposal is to find out how important photoheterotrophy is in the open ocean - the Earth's largest ecosystem, of profound importance to global biogeochemistry and climate. Photoheterotrophic prokaryotes use light for energy but cannot use carbon dioxide as their sole carbon source and consequently use organic molecules from the environment to satisfy their carbon requirements. Despite considerable advances in the understanding of several photoheterotrophic mechanisms the role of solar radiation in the metabolism of bacterioplankton in the ocean is difficult to assess, although it is already apparent that CO2 fixation by prokaryotic cells may be only a part of the picture. The project proposes to experimentally test and to examine by mathematical modelling a hypothesis that SAR11 alphaproteobacteria and Prochlorococcus cyanobacteria numerically dominate the open ocean because of their photoheterotrophy. Using a combination of laboratory and oceanic cruise experiments the following objectives will be addressed: (i) to determine uptake rates of phosphate and amino acids as a function of light intensity and spectrum by the main planktonic prokaryotic groups, SAR11 and Prochlorococcus, and to relate these rates to cyanobacterial rates of CO2 fixation; (ii) to quantify mesoscale spatial and depth-related variations of group-specific rates of light-enhanced uptake of phosphate and amino acids within the euphotic zone, linking these variations in photoheterotrophy with population sizes and composition of the dominant groups in the North Atlantic subtropical gyre; (iii) to compare photoheterotrophic rates in the North Atlantic gyre with the ones in the Southern gyre and the Equatorial region, using light-enhanced amino acid uptake in order to ascertain the significance of photoheterotrophic use of light at the ocean scale. In order to meet the above objectives we will focus on experimental work in the open Atlantic Ocean combining isotopic tracer nutrient bioassays with flow cytometric sorting of bacterioplankton cells followed by ultra-sensitive radioassaying of cells, cell identification by fluorescence in situ hybridization and nano-scale secondary-ion mass spectrometry in conjunction with molecular identification of prokaryotic cells by halogen in situ hybridisation. Our overarching aim is to establish the input of solar energy into the microbial world of the open ocean beyond that used for CO2 fixation.