Effects of silicate limitation on production of domoic acid, a neurotoxin, by the diatom Pseudo-nitzschia multiseries. I. Batch culture studies

Abstract

Dornoic acid (DA) production by Pseudo-nitzschia multiseries (Hasle) was studied at various silicate concentrations and under silicate perturbation. Both slowly dividing and non-dividing pop-ulation~ produced DA, and the production rates were inversely correlated with the ambient silicate concentrations. Production of DA was significantly enhanced when overall cell metabolism (i.e growth rate) declined as a result of silicate stress. Following silicate starvation, cultures supplemented with silicate registered uptake, but suspended DA production. Results suggest that luxury uptake of Si by P. multisenes may happen only in phys~ologically active populations, i.e, the exponential phase, but not in the stationary phase. There were 2 stages of DA production The first stage corresponded to a decline in growth caused by moderately low lcvels of remaining s~licate in the medium, wh.ile the second stage was caused by severe silicate limitation. The production rate during the second stage (13.67 to 30.20 fg DA cell-' d-') was about an order of magnitude higher than during the first stage (0.97 to 4.98 fg DA cell-' d-l). Increases and decreases in cellular DA content corresponded to decreases and increases in growth rates.