Copper limitation and toxicity in marine diatoms

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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.