Physical factors influencing the production of saxitoxin analogues in Gymnodinium catenatum and Alexandrium pacificum cultures

In vitro production of the common saxitoxin analogues C1+2 and B1 in the dinoflagellates
Gymnodinium catenatum and Alexandrium pacificum was determined in relation to several
natural physical parameters, such as temperature and oscillations in geomagnetic activity
(GMA) or solar activity (SA) derived from the 11-year sunspot cycle, such as the X-ray output.
Disulfated C1+2 toxin increased significantly with increasing temperature (from 17 to 28 °C)
and X-ray levels (from 0 to 8.5 A-level units) in G. catenatum. In A. pacificum, C1+2 decreased
significantly with X-ray levels. Toxin production did not change with GMA in G. catenatum,
while in A. pacificum a U-shaped hormetic dose response was observed, centred around the 7-20
nT interval. Oxidative stress induced by an extremely weak low-frequency magnetic field or
hydrogen peroxide also increased toxin levels. C1+2 toxin increased with natural variations in
physical parameters ranged between 120 and 200%, while artificial agents ranged from 110 to
160%. Intracellular concentrations of the bi-sulfated C1+2 were from 9 to 10 times higher than
the mono-sulfated B1. The relevance of sulfation observed is in accordance with the general
dominance of sulfated analogues in marine dinoflagellates.