THE ROLE OF COPPER FOR IRON ACQUISITION BY PSEUDO-NITZSCHIA IN THE JUAN DE FUCA EDDY

Liza M. McClintock¹, William P. Cochlan², Nicolas Ladizinsky², Charles G. Trick¹

¹Department of Biology, University of Western Ontario, London, Ontario, Canada
²Romberg Tiburon Center, San Francisco State University, Tiburon, California, USA

Toxigenic, pennate diatoms of the Pseudonitzschia genus are consistently found in the Juan de Fuca eddy region off the coast of British Columbia and Washington State. The toxin produced by these bloom-forming diatoms is domoic acid, a neurotoxin responsible for Amnesic Shellfish Poisoning. The function of domoic acid is unresolved, although the chemical structure of domoic acid is analogous to trace-metal chelators involved in acquisition or sequestration. The synergistic relationship between iron limitation and copper stress on Pseudonitzschia spp. was examined during a drifter study following the development of a toxic Pseudonitzschia spp. bloom in September 2004. Deckboard incubation experiments indicate that phytoplankton growth is enhanced by iron enrichments, while photosynthetic carbon uptake as a function of irradiance (P vs. E analysis) revealed that copper increases the photosynthetic efficiency of the Pseudonitzschia spp. dominated community. These results suggest that domoic acid may alleviate iron stress by complexing copper, which is required for a high efficiency iron uptake pathway into the cell. The production of domoic acid appears to provide a competitive advantage for Pseudonitzschia spp. when iron-limiting conditions prevail within the natural environment.