Development of an automatic system for cultivating the bioluminescent heterotrophic dinoflagellate Noctiluca scintillans on a 100-liter scale

Abstract

Noctiluca scintillans is a heterotrophic dinoflagellate that causes red-colored oceans during the day (red tides) andglowing oceans at night (bioluminescence). This species feeds on diverse prey, including phytoplankton, heterotrophicprotists, and eggs of metazoans. Thus, many scientists have conducted studies on the ecophysiology of this species. It iseasy to cultivate N. scintillans at a scale of <1 L, but it is difficult to cultivate them at a scale of >100 L because N. scintillanscells usually stay near the surface, while prey cells stay below the surface in large water tanks. To obtain mass-cultured N. scintillans cells, we developed an automatic system for cultivating N. scintillans on a scale of 100 L. The system consistedof four tanks containing fresh nutrients, the chlorophyte Dunaliella salina as prey, N. scintillans for growth, and N. scintillansfor storage, respectively. The light intensities supporting the high growth rates of D. salina and N. scintillans were 300and 20 μmol photons m-2 s-1, respectively. Twenty liters of D. salina culture from the prey culture tank were transferred tothe predator culture tank, and subsequently 20 L of nutrients from the nutrient tank were transferred to the prey culturetank every 2 d. When the volume of N. scintillans in the predator culture tank reached 90 L 6 d later, 70 L of the culturewere transferred to the predator storage tank. To prevent N. scintillans cells from being separated from D. salina cells inthe predator culture tank, the culture was mixed using an air pump, a sparger, and a stirrer. The highest abundance of N. scintillans in the predator culture tank was 45 cells mL-1, which was more than twice the highest abundance when thisdinoflagellate was cultivated manually. This automatic system supplies 100 L of N. scintillans pure culture with a highdensity every 10 d for diverse experiments on N. scintillans.