Abstract

The toxigenic diatom Pseudo-nitzschia cuspidata, isolated from the U.S. Pacific Northwest, was examined in unialgal batch cultures to evaluate domoic acid (DA) toxicity and growth as a function of light, N substrate, and growth phase. Experiments conducted at saturating (120μmol photons·m(-2) ·s(-1) ) and subsaturating (40μmol photons·m(-2) ·s(-1) ) photosynthetic photon flux density (PPFD), demonstrate that P. cuspidata grows significantly faster at the higher PPFD on all three N substrates tested [nitrate (NO3 (-) ), ammonium (NH4 (+) ), and urea], but neither cellular toxicity nor exponential growth rates were strongly associated with one N source over the other at high PPFD. However, at the lower PPFD, the exponential growth rates were approximately halved, and the cells were significantly more toxic regardless of N substrate. Urea supported significantly faster growth rates, and cellular toxicity varied as a function of N substrate with NO3 (-) -supported cells being significantly more toxic than both NH4 (+) - and urea-supported cells at the low PPFD. Kinetic uptake parameters were determined for another member of the P. pseudodelicatissima complex, P. fryxelliana. After growth of these cells on NO3 (-) they exhibited maximum specific uptake rates (Vmax ) of 22.7, 29.9, 8.98×10(-3) ·h(-1) , half-saturation constants (Ks ) of 1.34, 2.14, 0.28μg-at N·L(-1) , and affinity values (α) of 17.0, 14.7, 32.5×10(-3) ·h(-1) /(μg-at N·L(-1) ) for NO3 (-) , NH4 (+) and urea, respectively. These labo-ratory results demonstrate the capability of P. cuspidata to grow and produce DA on both oxidized and reduced N substrates during both exponential and stationary growth phases, and the uptake kinetic results for the pseudo-cryptic species, P. fryxelliana suggest that reduced N sources from coastal runoff could be important for maintenance of these small pennate diatoms in U.S. west coast blooms, especially during times of low ambient N concentrations.

Full Text
Published version (Free)

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call