Pseudo-nitzschia in culture
I have isolated 14 cultures from Maryland and Virginia waters and one culture from California.
Some of these cultures produce domoic acid.
Abundance and toxicity over 27 days for a batch culture of Pn-1 (P. multiseries from the Choptank River) under Silica limitation. The open squares represent cell abundance (cells/mL - left axis) and the filled diamonds represent domoic acid content (pg DA/cell - right axis).
Pseudo-nitzschia Growth Rates on Different Nitrogen Sources
Pseudo-nitzschia, like all plants, needs Nitrogen to grow. This Nitrogen can come from Nitrate (NO3), Ammonium (NH4), urea or dissolved amino acids. Pseudo-nitzschia cells must process different sources of Nitrogen differently to get at the actual Nitrogen atoms. Knowing which Nitrogen source is being utilized can give information about what the cell is doing and measuring growth rates can tell how well the cell is doing it.
Much of what we know about plankton comes from culture studies. Most Pseudo-nitzschia culture studies focus on P. multiseries with the results extrapolated to other species and strains. However, broad species and strain differences have been well documented (Elrifi and Turpin 1985, Larsen and Bryant 1998, Holmes et al. 1991, Wood and Leatham 1992) and draw into question the validity of making conclusions based on one or a few strains.
Growth rates for 8 cultures of Pseudo-nitzschia grown on either nitrate (blue), ammonia (purple) or urea (yellow). Not all cultures or species of Pseudo-nitzschia prefer the same nitrogen source. Most cultures have a preference or at least one nitrogen source they liked least. Bars with the same letter above them are not statistically different from each other. The statistical test compared the growth rates on NO3, NH4 and urea for each culture. Different cultures were not compared. For example the growth rate for Pn-15 NH4 was not compared to Pn-13 NH4.
Pseudo-nitzschia Growth Rates under Different Light Intensities
Pseudo-nitzschia also needs light to grow and live. Above are nine panels showing growth rates of three cultures over a range of light intensities (irradiance measured as number of photons hitting a square meter in one second) at three different temperatures, 10C, 15C and 20C. Row A is Pn-1 (P. multiseries). Row B is CLN47 (P. multiseries). Row C is Pn-15 (P. fraudulenta). Note that as the temperature increases so does the maximum growth rates (faster growth). The irradiance where growth saturates (reaches it's highest point) decreases as the temperature decreases. For example, culture Pn-1 has a maximum growth rate at 10C of about 0.2 and can grow that fast at only 100 irradiance. At 20C the maximum growth rate is about 1.0 at an irradiance of about 300.