Coccolithophore Mixotrophy

球石藻是一种单细胞藻类，被称为球石岩的石灰岩（方解石）板覆盖。它们可能构成了海洋中大部分的浮游植物生物量。球石藻通常被认为是自养生物，这意味着它们利用阳光作为能量来源，利用光合作用将碳固定在柔软的植物组织和坚硬的成矿方解石中（“自养”）。然而，越来越多的证据表明，球石藻是“混合营养”的，这意味着它们可以通过光合作用固定碳，也可以通过吞噬小有机颗粒和从海水中吸收其他简单碳分子在黑暗中生长。球石藻参与混合营养的程度可以影响碳向深海的转移。这项工作基本上是通过实验室和现场实验来量化球石藻混合营养（利用溶解和还原碳化合物作为能量的能力），并阐明其与海洋生物学和化学的相关性。这项工作将在三个方面产生更广泛的影响：1)培养本科生：在项目期间将培养两名REU本科生。该学生在第二年将参加研究巡航。2) cafe Scientifique项目：这项工作将在Bigelow Laboratory？s cafe Scientifique节目。这些是免费的公众聚会，公众被邀请参加关于海洋科学和技术的最新想法和问题的对话。3)数字电子书：我们建议制作一个数字电子书，专门强调和解释球石藻内的混合营养。混合营养球石藻的图像将是这本书的主要视觉元素。该电子书将公开发行，并分发给我们的教育分支机构科尔比学院。本书的目标是进一步传达微生物世界的复杂性，食物网动态，加上它们与全球碳循环的关系，激发对这些惊人生命形式的兴趣，教育和好奇心。球石藻可以显著影响大气中二氧化碳的减少，它们可以通过两种碳泵机制将二氧化碳从海洋表面转移到深海中并将其隔离：(1)“碱度泵”（也称为碳酸钙泵），海洋表面的球石藻吸收溶解的无机碳（DIC，主要是一种称为碳酸氢盐的形式，是海洋碱度的主要成分）。它们将一半转化为二氧化碳，要么作为植物生物量固定下来，要么作为气体释放出来，另一半则合成成它们的矿物球岩屑。因此，球石团钙化实际上可以在短时间尺度（即数周）内增加表面二氧化碳。然而，经过几个月到几年的时间，球石沉入数千米以下，在那里它们溶解并将碳酸氢盐释放回深水中。因此，下沉的球粒岩本质上是将碳酸氢盐碱度从表面“泵”到深海，而这些碳在深海深处被隔离了数千年。(2)“生物泵”，致密的石灰岩球砾岩的压舱效应加速了有机软组织碎片（颗粒有机碳或POC）的下沉，本质上是将这些软碳组织“泵”到深处。生物泵最终减少了表面二氧化碳。软组织和碱度泵在维持DIC的垂直梯度方面相互加强（比表面更深入），但在二氧化碳的海气交换方面它们相互对立。因此，球石藻对大气CO2的净效应取决于其与碱度泵相关的CO2升高效应和与软组织生物泵相关的CO2降低效应的平衡。事实上，人们总是认为球粒有机碳（PIC）完全来自溶解有机碳（DIC，如碳酸氢盐），而不是溶解有机碳（DOC）。本提案的目标是描述a)一系列DOC化合物被球石藻吸收和同化的可能性，b) DOC被球石藻吸收的速率和可能被纳入PIC球石藻的可能性，如果这是真的，将代表碱度泵范式的重大转变。这项工作基本上是通过实验室和现场实验来量化球石藻混合营养，并阐明其与海洋生物学和化学的相关性。已经有许多技术进步来解决这个问题，所有这些都将应用于这项工作。调查人员将：(a)屏幕coccolithophore文化吸收和同化的大阵的DOC分子,(b)执行分子示踪实验与特定的医生为了研究吸收environmentally-realistic浓度,(c)测量固定医生到有机组织,独立于固定到图片颗石藻,(d)单独的颗石藻从其他浮游植物和细菌利用流式细胞术和e)区分这些排序coccolithophore细胞的营养方式。这项工作将从根本上推进海洋中球石藻混合营养的知识状态，并解决自养和异养来源的球石藻碳平衡问题。

Coccolithophores are single-cell algae that are covered with limestone (calcite) plates called coccoliths. They may make up most of the phytoplankton biomass in the oceans. Coccolithophores are generally considered to be autotrophs, meaning that they use photosynthesis to fix carbon into both soft plant tissue and hard minerogenic calcite, using sunlight as an energy source ("autotrophic"). However, there is an increasing body of evidence that coccolithophores are "mixotrophic", meaning that they can fix carbon from photosynthesis as well as grow in darkness by engulfing small organic particles plus taking up other simple carbon molecules from seawater. The extent to which Coccolithophores engage in mixotrophic can influence the transfer of carbon into the deep sea. This work is fundamentally directed at quantifying coccolithophore mixotrophy -- the ability to use dissolved and reduce carbon compounds for energy -- using lab and field experiments plus clarifying its relevance to ocean biology and chemistry. This work will generate broader impacts in three areas: 1) Undergraduate training: Two REU undergraduates will be trained during the project. The student in the second year will participate in the research cruise. 2) Café Scientifique program: This work will be presented in Bigelow Laboratory?s Café Scientifique program. These are free public gatherings where the public is invited to join in a conversation about the latest ideas and issues in ocean science and technology. 3) Digital E-Book: We propose to make a digital E-book to specifically highlight and explain mixotrophy within coccolithophores. Images of mixotrophic coccolithophores would be the primary visual elements of the book. The E-book will be publically available and distributed to our educational affiliate, Colby College. The goal of the book is to further communicate the intricacies of the microbial world, food web dynamics, plus their relationship to the global carbon cycle, to inspire interest, education, and curiosity about these amazing life forms.Coccolithophores can significantly affect the draw-down of atmospheric CO2 and they can transfer CO2 from the surface ocean and sequester it in the deep sea via two carbon pump mechanisms: (1) The "alkalinity pump" (also known as the calcium carbonate pump), where coccolithophores in the surface ocean take up dissolved inorganic carbon (DIC; primarily a form called bicarbonate, a major constituent of ocean alkalinity). They convert half to CO2, which is either fixed as plant biomass or released as the gas, and half is synthesized into their mineral coccoliths. Thus, coccolithophore calcification can actually increase surface CO2 on short time scales (i.e. weeks). However, over months to years, coccoliths sink below thousands of meters, where they dissolve and release bicarbonate back into deep water. Thus, sinking coccoliths essentially "pump" bicarbonate alkalinity from surface to deep waters, where that carbon remains isolated in the abyssal depths for thousands of years. (2) The "biological pump", where the ballasting effect of the dense limestone coccoliths speeds the sinking of organic, soft-tissue debris (particulate organic carbon or POC), essentially "pumping" this soft carbon tissue to depth. The biological pump ultimately decreases surface CO2. The soft-tissue and alkalinity pumps reinforce each other in maintaining a vertical gradient in DIC (more down deep than at the surface) but they oppose each other in terms of the air-sea exchange of CO2. Thus, the net effect of coccolithophores on atmospheric CO2 depends on the balance of their CO2-raising effect associated with the alkalinity pump and their CO2-lowering effect associated with the soft-tissue biological pump. It is virtually always assumed that coccolith particulate organic carbon (PIC) originates exclusively from dissolved organic carbon (DIC, as bicarbonate), not dissolved organic carbon (DOC). The goal of this proposal is to describe a) the potential uptake and assimilation of an array of DOC compounds by coccolithophores, b) the rates of uptake, and potential incorporation of DOC by coccolithophores into PIC coccoliths, which, if true, would represent a major shift in the alkalinity pump paradigm. This work is fundamentally directed at quantifying coccolithophore mixotrophy using lab and field experiments plus clarifying its relevance to ocean biology and chemistry. There have been a number of technological advances to address this issue, all of which will be applied in this work. The investigators will: (a) screen coccolithophore cultures for the uptake and assimilation of a large array of DOC molecules, (b) perform tracer experiments with specific DOC molecules in order to examine uptake at environmentally-realistic concentrations, (c) measure fixation of DOC into organic tissue, separate from that fixed into PIC coccoliths, (d) separate coccolithophores from other phytoplankton and bacteria using flow cytometry and e) distinguish the modes of nutrition in these sorted coccolithophore cells. This work will fundamentally advance the state of knowledge of coccolithophore mixotrophy in the sea and address the balance of carbon that coccolithophores derived from autotrophic versus heterotrophic sources.