Optimal temperature and photoperiod for the cultivation of Agardhiella subulata microplantlets in a bubble‐column photobioreactor

The optimal temperature and illumination photoperiod requirements for the phototrophic growth of a novel microplantlet suspension culture derived from the macrophytic marine red alga Agardhiella subulata were determined. The optimal growth temperature was 24°C. The effects of illumination light‐dark (LD) photoperiod (hour of light:hours of darkness within a 24 h cycle) on biomass production was studied within a bubble‐column photobioreactor. The 4.5 cm diameter photobioreactor was maintained at near‐saturation conditions with respect to light flux (38 μmol photons m −2 s −1 ), nutrient medium delivery (20% nutrient replacement per day), and CO 2 delivery (0.35 mmol CO 2 L −1 h −1 ) so that the cumulative effects of photodamage on the cell density versus time curve at photoperiods approaching continuous light could be observed. Biomass production was maximized at 16:8 LD, where biomass densities exceeding 3.6 g dry cell mass L −1 were achieved after 60 days in culture. Biomass production was proportional to photoperiod at low fractional photoperiods (≤10:14 LD), but high fractional photoperiods approaching continuous light (≥ 20:4 LD) shut down biomass production. Biomass production versus time profiles under resource‐saturated cultivation conditions were adequately described by a cumulative photodamage growth model, which coupled reversible photodamage processes to the specific growth rate. Under light‐saturated growth conditions, the rate constant for photodamage was k d = 1.17 ± 0.28 day −1 (±1.0 SE), and the rate constant for photodamage repair was k r = 5.12 ± 0.95 day −1 (±1.0 SE) at 24°C. © 2002 Wiley Periodicals, Inc. Biotechnol Bioeng 79: 135–144, 2002.