Effect of environmental and nutritional factors on growth and azaspiracid production of the dinoflagellate Azadinium spinosum

Abstract

Azadinium spinosum, a small dinoflagellate isolated from the North Sea, is a producer of azaspiracids (AZAs), a group of biotoxins associated with human illness following ingestion of contaminated shellfish. Using batch and continuous cultures of A. spinosum, the present study investigated the effects of different environmental and nutritional factors (salinity, temperature, photon flux density, aeration, culture media, nitrogen sources, phosphate source, and N/P ratios) on growth, maximum cell concentration, and AZA cell quota.Azadinium spinosum grew in a wide range of conditions; from 10̊C to 26̊C and salinities from 30 to 40, under irradiances ranging from 50μmolm−2s−1 to 250μmolm−2s−1, with or without aeration. Growth and maximum cell concentration were highest at a salinity of 35, at temperatures between 18̊C and 22̊C, and with aeration. Concerning AZA cell quota, the most significant effect was observed at low temperature; the AZA cell quota was more than 20 times higher at 10̊C (220fgcell−1) than at temperatures between 18̊C and 26̊C. A. spinosum grew on all media tested with only slight differences in growth rate and AZA cell quota. In continuous culture, lowering the concentration of nutrients (0.5 strength of a modified K-medium) in the inflow improved AZA cell quota whereas higher concentration (doubling the normal strength of K-medium) improved maximal cell concentration. A. spinosum grew on different sources of nitrogen tested (nitrate, urea, ammonium) with almost no effect on toxin cell quota and growth, except that adding ammonium caused a decrease in growth.These first experiments on Azadinium spinosum increased our knowledge on factors affecting its growth and toxin production; furthermore, these results allowed and improved particularly A. spinosum production in pilot scale photobioreactors for AZA isolation.