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

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.