Filamentous cell cultures derived from female gametophytes of the temperate brown macroalga Laminaria saccharina were photolithotrophically cultivated in artificial seawater medium within an illuminated 1.3-L stirred-tank bioreactor at 13 degrees C using CO2 in air as the carbon source. A Monod model adequately described light-saturated growth. The apparent half-saturation constant (K-o) was 23 mu E/m(2)-s, and maximum specific growth rate was 0.15 day(-1). At a constant inoculation cell density of 50 mg DCW/L, biomass productivity after 26 days of cultivation increased from 630 mg DCW/L at 18 mu E/m(2)-s to 890 mg DCW/L at 228 mu E/m(2)-s. At 98 mu E/m(2)-s, 1.1 vvm aeration rate, and 250 rpm impeller speed, the CO2 transfer rates (CO2 TRs) and CO2 consumption rates (r(CO2)) were determined over the cultivation period. At peak CO2 demand, the maximum CO2 TR was 0.19 mmol CO2/L-h, but r(CO2) was only 0.15 mmol CO2/L-h, implying that the culture was not CO2 transport limited. This is the first reported bioreactor cultivation study of cell cultures derived from a macrophytic marine alga.