| Macrophytic marine algae are a rich source of unique natural products. Controlled biological production of these compounds first requires the development of an engineered biomass production system to illustrate the application of bioprocess engineering principles to this new area of marine biotechnology. Toward this end, two axenic liquid suspension cultures were established for Agardhiella subulata, including an undifferentiated filament clump culture established by induction of callus-like tissue from thallus explants, and a microplantlet culture established by regeneration of callus filaments. The microplantlet culture was selected for bioreactor cultivation studies because it was morphologically stable.; Controlled cultivation of Agardhiella subulata microplantlet suspension was successful in both externally-illuminated bubble-column and stirred-tank bioreactors. Limiting process parameters on biomass production, including temperature, pH, CO2 delivery, light transfer, macronutrient consumption, agitation intensity, and microplantlet morphology were assessed. The optimal growth temperature was 24°C. The optimal pH environment for cultivation was centered around pH 8. The growth was not CO2-limited in either bioreactor system when aerated at 0.3 vvm containing 3500 ppm CO 2 in the aeration gas. Light transfer limitations were addressed by comparing the mean light intensity (Im) to the light intensity at 63% of photosynthetic saturation (Ik). The optimal photoperiod was 16:8 LD. The biomass yield coefficients based on N and P during the bioreactor cultivation were 1.0 gDCW/mmol N and 26.0 gDCW/mmol P respectively. Medium perfusion rate of 20% per day during bioreactor cultivation prevented nitrate and phosphate depletion, maintained the specific oxygen evolution rate at 0.12 mmol O2 g−1 DCW h−1, and prolonged active growth phase. Two exponential phases of growth were observed during prolonged biomass production under resource-saturated conditions. Bubble aeration did not fragment the plantlets. Impeller rotation rates from 60 and 250 rpm in the 500 mL, stirred tank bioreactor did not affect the specific growth rate during the exponential phase of growth. |
