The Comparison between Toxic Pseudo-nitzschia multiseries (Hasle) Hasle and Non-toxic P. pungens (Grunow) Hasle Isolated from Jinhae Bay, Korea

We studied the ecological characteristics of Pseudo-nitzschia multiseries and P. pungens, comparing the morphology, toxin production, growth and ITS sequences. On the basis of transmission electron microscopy (TEM), it was found that P. pungens had 9-12 fibulae in 10 mu m, 2 rows of poroids, 3-4 poroids in 1 mu m and 9-11 striae in 10 mu m, while in P. multiseries 13-14 fibulae in 10 mu m, 3-4 rows of poroids, 4-6 poroids in1 mu m and 13-14 striae in 10 mu m. Domoic acid (DA) production by P. multiseries was determined by HPLC with UV or fluorometric detection, and resulted in 221.8 ng times mL super(-1), 196.4 ng times mL super(-1) and 25.4 ng times mL super(-1) in the whole culture, cell-free medium and cell fraction, respectively, for 20 days at 20 degree C under light intensity of 100 mu mol times m super(-2) times s super(-1) with 16:8 LD cycle, while values for P. pungens were negative. Both P. multiseries and P. pungens showed a higher growth rate at higher temperature with the highest growth rate at 20 degree C. Pseudo-nitzschia multiseries had a wide range of salinity (20-40 psu) for optimal growth, but at 40 psu and 50 psu, the growth rate of P. pungens was lower than that of P. multiseries. In particular, 10 psu did not allow any growth of P. multiseries. For nitrate, ammonium and urea-grown cultures, nutrient concentration contributed to a variation of growth, in which the best growth was obtained at 100 mu M. However, P. multiseries grew well even in a medium without urea, while the growth rate of P. pungens was significantly different (p < 0.05). The influence on growth rate was less in cultures grown with phosphorus than with nitrogen sources. However, under a wide range of pH and depleted conditions of trace metals and vitamins, P. multiseries and P. pungens had similar growth rates. The alignment of nucleotide sequences for the internal transcribed spacer (ITS) regions showed that there were considerable conserved sites of 290 bp, 68 variable sites (19%) in P. multiseries and 119 (29%) in P. pungens. In the predicted secondary structures, P. multiseries and P. pungens had a similar free energy, conformation and structural stabilization, but stem structures were different.