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养在开阔海洋中的重要性，开阔海洋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。光异养原核生物使用光作为能量，但不能将二氧化碳作为其唯一的碳源，因此使用来自环境的有机分子来满足其碳需求。尽管对几种光异养机制的理解取得了相当大的进展，但太阳辐射在海洋浮游细菌代谢中的作用仍难以评估，尽管原核细胞对二氧化碳的固定可能只是其中的一部分已经很明显。该项目建议通过实验测试和数学建模来检验一个假设，即SAR11 α变形菌和原绿球菌蓝藻由于其光异养性而在数字上占主导地位。将利用实验室实验和海洋巡航实验相结合的方法，实现以下目标：(i)确定主要浮游原核生物类群SAR11和原绿球藻对磷酸盐和氨基酸的吸收速率与光强度和光谱的关系，并将这些速率与蓝藻的二氧化碳固定速率联系起来；（ii）量化光增强带内不同种群对磷酸盐和氨基酸吸收速率的中尺度空间和深度相关变化，将这些光异养变化与北大西洋副热带环流中优势种群的种群规模和组成联系起来；（iii）比较北大西洋环流与南环流和赤道地区的光异养率，利用光增强的氨基酸摄取，以确定光在海洋尺度上的光异养利用的意义。为了实现上述目标，我们将在开放的大西洋开展实验工作，将同位素示踪营养生物测定与浮游细菌细胞的流式细胞分选结合起来，然后进行细胞的超灵敏放射测定，荧光原位杂交和纳米二级离子质谱法进行细胞鉴定，并结合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输入到开放海洋的微生物世界，而不是用于二氧化碳固定。

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.