Copper limitation and toxicity in marine diatoms

公海表层水域含有一些地球上任何环境中最低水平的痕量金属，但由于灰尘的输入和深水的上涌，它们瞬间暴露在浓度升高的环境中。这些浓度的巨大变化意味着生活在这些地区的光合作用微生物可能会暴露在有时不足以生长、有时会抑制生长的水平下。铜是一种重要的痕量金属，因为它是参与关键生化反应的酶和氧化还原蛋白中的重要辅助因子，也是毒性最大的元素之一。然而，我们对铜如何影响硅藻的生长，以及它们如何适应和适应环境中铜的可获得性变化，知之甚少。硅藻是生活在海洋中的一群重要的单细胞初级生产者。这项研究的目的是：1)描述海洋和沿海硅藻铜调控的转录组，并确定铜缺乏和铜毒害下差异表达的基因；2)量化铜吸收基因同源物的转录调控；3)测量细胞外铜还原并确定其在铜吸收中的作用；4)确定硅藻种源如何影响铜的动态平衡；5)开发与硅藻铜营养状态相关的分子标记，并将其应用于评估海洋中铜的有效性。这项拟议的研究是阐明控制浮游植物生长的因素的持续努力的一部分。它将提供对硅藻中铜的动态平衡的机械理解，并确定海洋中铜有效性变化的潜在生态和生物地球化学后果。这项工作是及时的，因为据预测，海洋酸化将极大地增加某些无机铜物种的浓度，并影响铜络合作用。硅藻如何受到这些变化的影响尚不确定，因为我们对硅藻吸收和解毒铜的机制有一个初步的了解，而对可用于细胞运输的铜物种类型知之甚少。这里概述的研究将开始填补这些知识空白。

Surface waters of the open sea contain some of the lowest levels of trace metals of any environment on Earth, yet are transiently exposed to elevated concentrations via inputs from dust and upwelling from deep waters. These large variations in concentration mean that the photosynthetic microbes living in these regions can be exposed to levels that are at times inadequate for growth and at other times inhibitory. Copper is an important trace metal because of its role as an essential co-factor in enzymes and redox proteins involved in key biochemical reactions and because it is one of the most toxic. Yet, we know little about how copper affects growth of diatoms, an important group of single-celled primary producers living in the sea, or the ways in which they acclimate and adapt when copper availability changes in the environment. The aims of this research proposal are: 1) to describe the copper-regulated transcriptome of an oceanic and coastal diatom and identify differentially expressed genes under copper deficiency and toxicity, 2) to quantify transcriptional regulation of copper uptake gene homologs, 3) to measure extracellular copper reduction and determine its role in copper uptake, 4) to determine how diatom provenance affects copper homeostasis, and 5) to develop molecular markers that correlate with the copper nutritional state of diatoms and apply them to assess copper availability in the ocean. The proposed research is part of a continuing effort to elucidate the factors regulating phytoplankton growth. It will provide a mechanistic understanding of copper homeostasis in diatoms and identify the potential ecological and biogeochemical consequences of variations in copper availability in the sea. The work is timely given that ocean acidification is predicted to greatly increase the concentration of some inorganic species of copper and affect copper complexation. How diatoms might be affected by these changes is uncertain as we have a rudimentary understanding of their mechanisms of copper uptake and detoxification and know little about the types of copper species that are available for cellular transport. The research outlined here will begin to fill these gaps in knowledge.