Optimization of growth and production of toxins by three dinoflagellates in photobioreactor cultures

Abstract

A bioreactor system for biotoxin production was appraised against traditional methods of growing dinoflagellate cultures. In an optimised bioreactor culture (5.4 L) operated in batch mode, growth of Karenia selliformis was more efficient than in 15-L bulk carboy culture in terms of growth rate (μ = 0.07 day⁻¹ versus 0.05 day⁻¹) and growth maximum (G _max, 169.10⁶ versus 41.10⁶ cells L⁻¹). Maximal gymnodimine concentration (1200 μg L⁻¹) in bioreactor culture was 8-fold higher than in bulk carboy culture, and the yield per cell (pg cell⁻¹) was 2-fold higher. Similarly the bioreactor batch culture of Alexandrium ostenfeldii performed more efficiently than carboy cultures in terms of growth rate (1.6-fold higher), growth maximum (15-fold higher) and desmethyl C spirolide (SPX-desMe-C) yield (5-fold higher [μg L⁻¹], though the yield [pg cell⁻¹basis] was lower). When bioreactor cultures of K. selliformis were operated in continuous mode, the yield of gymnodimine was substantially higher than a carboy or the bioreactor run in batch mode to growth max (793 μg day⁻¹ over 58 days in continuous culture was achieved versus an average of 60 μg day⁻¹ [carboy over 40 days] or 249 μg day⁻¹ [batch mode] over 26 days). Likewise in continuous bioreactor cultures of A. ostenfeldii run over 25 days, the yield of SPX-desMe-C (29 μg day⁻¹) was substantially higher than in same cultures run in batch mode or carboys (10.2 day⁻¹ and 7.7 μg day⁻¹ respectively). Similarly 5.4 L bioreactor batch cultures of K. brevisulcata reached 3.8-fold higher cell densities than carboy cultures, and when operated in continuous mode, the brevisulcatic acids were more efficiently produced than in batch culture (12 μg day⁻¹ versus 7 μg day⁻¹). When the bioreactor system was upscaled to 52 L, the maximum cell densities and toxin yields of K. brevisulcata cultures were somewhat less than those achieved in the smaller reactor, which was attributed to reduced light penetration.