Pathways of copper acquisition in phytoplankton

浮游植物对金属的吸收至关重要，因为它将环境中金属的反应性与其对生物体的生理和生态影响联系起来。了解金属是如何被吸收的，使我们能够预测哪些化学形式的金属是生物可利用的，以及哪些类型的浮游植物会对其浓度的变化做出反应。硅藻和蓝藻是对水生生态系统具有重要意义的两类浮游植物。它们生长在地球上金属含量最低的开阔海域的地表水中，尽管由于灰尘的输入和深水的上升流，它们暂时暴露在高浓度的环境中。铜（Cu）之所以引起人们的兴趣，是因为它是浮游植物生长所必需的金属，也是毒性最大的金属之一。浮游植物调整它们的吸收系统来缓冲环境中金属浓度的变化，以维持最佳的细胞水平，但吸收途径的细节现在才被揭示出来。铜被海洋硅藻通过一种吸收途径利用，该途径使用Cu的化学还原形式Cu(I)。Cu(I)是通过细胞还原产生的，但对细胞还原是如何调节的，以及其他浮游植物是否以同样的方式获取Cu知之甚少。其他群体，如蓝藻，可能使用不同的途径来吸收铜，因此与硅藻相比，对不同化学形式的铜产生反应。例如，蓝藻会产生结合铜的化合物来解毒，从而改变水中铜的化学性质，从而改变其对其他物种的可利用性。本研究的目的是：1)测量硅藻和蓝藻中Cu营养状态对Cu化学物质的生物利用度；2)评估不同浮游植物分类群中Cu（II）还原摄取途径的普遍程度及其在光作用下的激活；3)描述两种蓝藻中Cu调控的转录组，并鉴定铜缺乏诱导的差异表达基因，包括可能的Cu转运基因。这项拟议中的研究是一项持续努力的一部分，目的是阐明调节海洋浮游植物生长的因素。它将为两个生态上重要的浮游植物群的代表提供对铜吸收的机制理解，并确定铜可利用性变化的潜在生态和生物地球化学后果。由于海洋酸化预计会使某些无机Cu的浓度大大增加，并影响溶解有机物对Cu的络合作用，因此这项工作是及时的。浮游植物将如何受到这些变化的影响是不确定的，因为我们对它们的铜吸收机制有初步的了解，对可用于细胞运输的铜种类类型知之甚少。这里概述的研究将开始填补这些知识空白。

Metal uptake by phytoplankton is fundamentally important because it links the reactivity of metals in the environment to their physiological and ecological effects in the organisms. Understanding how metals are taken up enables us to predict which chemical forms of metals are bioavailable and which types of phytoplankton will respond to changes in their concentrations. Diatoms and cyanobacteria are two groups of phytoplankton of great significance to aquatic ecosystems. They grow in the open sea in surface waters containing some of lowest levels of metals on Earth although they are exposed to high concentrations transiently because of inputs from dust and upwelling from deep waters. Copper (Cu) is of interest because it is an essential metal for phytoplankton growth and one of the most toxic. Phytoplankton adjust their uptake systems to buffer changes in metal concentrations in the environment to maintain optimal cellular levels, but the details of the uptake pathways are only now being revealed. Copper is utilized by oceanic diatoms by an uptake pathway that uses a chemically reduced form of Cu, Cu(I). The Cu(I) is produced by cellular reduction, but little is known about how cellular reduction is regulated or whether other phytoplankton acquire Cu in the same way. Other groups, like cyanobacteria, may use different pathways for Cu uptake and hence react to different chemical forms of Cu than diatoms. Cyanobacteria, for example, produce compounds that bind Cu to detoxify it, changing the chemistry of Cu in the water and thereby altering its availability to other species. The aims of this research proposal are: 1) to measure the bioavailability of Cu chemical species as a function of Cu nutritional state of diatoms and cyanobacteria, 2) to assess the prevalence of the Cu(II) reduction uptake pathway among different taxonomic groups of phytoplankton and its activation by light, and 3) to describe the Cu-regulated transcriptome of two cyanobacteria and identify differentially expressed genes including putative Cu transport genes induced by Cu deficiency. The proposed research is part of a continuing effort to elucidate the factors regulating phytoplankton growth in the sea. It will provide a mechanistic understanding of Cu uptake by representatives of two ecologically important groups of phytoplankton and identify the potential ecological and biogeochemical consequences of variations in Cu availability. The work is timely given that ocean acidification is predicted to greatly increase the concentration of some inorganic species of Cu and affect Cu complexation by dissolved organic matter. How phytoplankton will be affected by these changes is uncertain as we have a rudimentary understanding of their mechanisms of Cu uptake and know little about the types of Cu species that are available for cellular transport. The research outlined here will begin to fill these gaps in knowledge.