ACCUMULATION OF DOMOIC ACID BY THE COASTAL DIATOM PSEUDO‐NITZSCHIA MULTISERIES: A POSSIBLE COPPER COMPLEXATION STRATEGY

Domoic acid (DA) is a neurotoxic amino acid produced by several members of the diatom genus Pseudo‐nitzschia. Trophic transfer of DA up the food chain has been implicated in the deaths of 100's of marine birds and marine mammals along the central California Coast. The physiological function of DA in Pseudo‐nitzschia spp. has not been defined, although some evidence indicates that elevated metal concentrations can induce DA accumulation (Subba RAO et al., 1998, P.S.Z.N. Mar. Ecol. 19:31). Although California coastal waters have experienced a decline in several heavy metals from 1977–1990, copper concentrations have increased by as much as 25% (Stephenson, M. D. & Leonard, G. H., 1994, Mar. Poll. Bull. 28:148). Many algae produce chelators, including amino acids, in response to toxic Cu²+] (Wu et al. 1998, J. Phycol. 34: 113). Domoic acid, a tricarboxylic acid, has 4 functional groups that may readily form chelation complexes with transition metals like copper. Copper enrichment experiments indicate that while Cu²+ is toxic to Pseudo‐nitzschia multiseries at total Cu] greater than 16.1μM (pCu 6.0), intracellular DA accumulation increases up to this point with no decline in growth rates relative to cultures grown in standard enriched seawater. These data suggest that DA may be accumulated by P. multiseries to mitigate the toxicity of elevated Cu²+]. Chemiluminescence will be used to quantify the binding affinity (expressed as conditional stability constants, Kc) of DA for Cu²+. Defining the Cu‐DA dose response relationship in Pseudo‐nitzschia can facilitate prediction of future toxic bloom events.