Alexandrium ostenfeldii growth and spirolide production in batch culture and photobioreactor

Growth and spirolide production of the toxic dinoflagellate Alexandrium ostenfeldii (Danish strain CCMP1773) were studied in batch culture and a photobioreactor (continuous cultures). First, batch cultures were grown in 450 mL flasks without aeration and under varying conditions of temperature (16 and 22 °C) and culture medium (L1, f/2 and L1 with addition of soil extract). Second, cultures were grown at 16 °C in 8 L aerated flat-bottomed vessels using L1 with soil extract as culture medium. Finally, continuous cultures in a photobioreactor were conducted at 18 °C in L1 with soil extract; pH was maintained at 8.5 and continuous stirring was applied.This study showed that A. ostenfeldii growth was significantly affected by temperature. At the end of the exponential phase, maximum cell concentration and cell diameter were significantly higher at 16 °C than at 22 °C. In batch culture, maximum spirolide quota per cell (approx. 5 pg SPX 13-desMeC eq cell−1) was detected during lag phase for all conditions used. Spirolide quota per cell was negatively and significantly correlated to cell concentration according to the following equation: y = 4013.9x−0.858. Temperature and culture medium affected the spirolide profile which was characterized by the dominance of 13,19-didesMeC (29–46%), followed by SPX-D (21–28%), 13-desMeC (21–23%), and 13-desMeD (17–21%).Stable growth of A. ostenfeldii was maintained in a photobioreactor over two months, with maximum cell concentration of 7 × 104 cells mL−1. As in batch culture, maximum spirolide cell quota was found in lag phase and then decreased significantly throughout the exponential phase. Spirolide cell quota was negatively and significantly correlated to cell concentration according to the equation: y = 12,858x−0.8986. In photobioreactor, spirolide profile was characterized by higher proportion of 13,19-didesMeC (60–87%) and lower proportions of SPX-D (3–12%) and 13-desMeD (1.6–10%) as compared to batch culture.

► A. ostenfeldii growth was significantly affected by temperature but not by medium composition.
► Spirolide quota per cell was negatively and significantly correlated to cell concentration both in batch and photobioreactor cultures.
► Spirolide profiles were affected by culture mode (batch vs photobioreactor).