OPP-PRF: The Role of Southern Ocean Iron limited Diatoms in Modulating Copper Speciation

生活在南大洋的被称为浮游植物的微生物有可能通过光合作用将大气中的碳转移到海洋中，从而降低大气中的碳含量。为了实现这一目标，浮游植物需要至关重要的微量营养元素铁，但南大洋的铁浓度通常太低，最终抑制了浮游植物的生长。一种特殊类型的浮游植物硅藻受到低铁水平的不成比例的影响，但就碳吸收和向深海运输而言，它们是浮游植物群落的重要成员。当铁含量太低而无法维持光合作用等生物过程时，硅藻会增加对铜等其他微量营养素的需求，以继续执行各种生物功能。为了满足增加的铜需求，硅藻可能会产生一种被称为配体的有机化合物，这种化合物可以结合铜等金属，并促进其进入细胞。这些配体可能帮助硅藻获得为各种生物系统提供燃料所需的额外铜。到目前为止，关于硅藻是否真的产生这些配体，触发配体产生的阈值，以及这些配体在海洋环境中的化学结构，我们知之甚少。该项目将重点回答这些问题，以增加我们对浮游植物如何适应低铁水平以维持其影响大气碳的生物系统的理解。南大洋是全球碳吸收的重要海洋盆地。然而，浮游植物，特别是硅藻的生长受到该地区微量营养元素铁的限制，阻止了额外的光合作用和碳吸收。当硅藻的铁含量有限时，它们会增加对铜的需求，为它们的铁运输系统和其他生物功能提供燃料。硅藻可以产生有机铜结合配体，以促进额外铜的吸收并将其纳入细胞。来自南极半岛西部的初步数据显示，这些水域含有强铜结合配体，而在富含铁的沿海水域，则没有强铜结合配体。南极半岛西部是南大洋的一个区域，其近海水域的铁含量较低。本研究将侧重于表征和鉴定该区域内的铜配体，以及确定硅藻在受铁限制时是否产生铜配体。还将探讨导致铜配体生产的微量金属阈值。利用存档的样品，在该区域发现的配体的化学结构将通过液相色谱和电感耦合等离子体和电喷雾电离质谱技术来确定，而配体的结合强度将通过利用竞争配体的电化学技术来确定。南大洋硅藻菌株将用于培养实验，并用不同浓度的铜和铁处理，以确定哪些菌株和在什么条件下硅藻产生铜结合配体。从培养实验中鉴定的配体将与在南大洋中从存档样本和南极半岛西部收集的数据中发现的配体进行比较。这个项目的发现将使人们更好地了解南大洋硅藻在铜需求增加时是如何适应的，以及这如何影响该地区储存碳的能力。该奖项反映了美国国家科学基金会的法定使命，并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，被认为值得支持。

Microscopic organisms called phytoplankton that live in the Southern Ocean have the potential to lower atmospheric carbon by transferring it into the ocean through photosynthesis. In order to achieve this, phytoplankton require the vital micro-nutrient iron, but concentrations of iron in the Southern Ocean are generally too low and ultimately inhibit phytoplankton growth. A particular type of phytoplankton called diatoms are disproportionately impacted by low levels of iron, yet they are important members of the phytoplankton community in terms of carbon uptake and transport to the deep ocean. When iron levels get too low to sustain biological processes like photosynthesis, diatoms increase their demand for other micro-nutrients like copper in order to continue to perform various biological functions. To meet their increased copper needed, diatoms may produce organic compounds known as ligands which can bind metals like copper and facilitate its uptake into the cell. These ligands likely help diatoms acquire the extra copper needed to fuel various biological systems. Thus far, little is known about whether diatoms do indeed produce these ligands, what thresholds trigger the production of ligands, and what the chemical structures of these ligands are in the marine environments. This project will focus on answering these questions to increase our understanding of how phytoplankton adapt to low iron levels to sustain their biological systems which can affect atmospheric carbon. The Southern Ocean is an important ocean basin for global carbon uptake. However, phytoplankton and in particular diatom growth is limited by the micronutrient iron in this region, preventing additional photosynthesis and carbon draw down. When diatoms are iron-limited they increase their requirements for copper to fuel their iron transport systems and other biological functions. Diatoms may produce organic copper-binding ligands to facilitate the uptake of additional copper and incorporate it into the cell. Preliminary data from the Western Antarctic Peninsula, a region of the Southern Ocean highlighted by iron limitation in offshore waters, showed these waters contained strong copper binding ligands, while in the iron replete coastal waters there was an absence of strong copper binding ligands. This research will focus on characterizing and identifying the copper ligands within this region as well as determining whether diatoms produce copper ligands when they are limited by iron. The trace metal thresholds that lead to copper ligand production will also be explored. Utilizing archived samples, the chemical structure of the ligands found in this region will be determined through liquid chromatography coupled with an inductively coupled plasma and electrospray ionization mass spectrometry technique, while the binding strength of the ligands will be determined through electrochemical techniques utilizing a competing ligand. Strains of Southern Ocean diatoms will be used in culturing experiments and treated with varying concentrations of copper and iron to determine what strains and under what conditions diatoms produce copper binding ligands. The ligands identified from cultured experiments will be compared to ligands found in the Southern Ocean from archived samples and data collected in the Western Antarctic Peninsula. Findings from this project will lead to a greater understanding of how Southern Ocean diatoms adapt when their copper demands increase, as well as how this affects the region’s ability to store carbon.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.