Growth characteristics of shade-acclimated marine Chlorella vulgaris under high-cell-density conditions

Aim : To potentially improve the productivity of microalgae for mass culture, growth characteristics and light-saturation index (E-k) in the marine microalga Chlorella vulgaris were investigated under high-cell-density conditions grown in batch cultures. Methodology : Potential changes in the growth characteristics and E-k in C. vulgaris were investigated during 4 weeks of cultivation. The algae was cultivated in a column reactor at 25 degrees C under a surface light intensity of 300 mu E m(-2) s(-1) in a 12-hr light and 12-hr dark cycle. Results : Cell density increased and reached 2.7 g-dw l(-1) by the end of culture with an areal production rate of 3.3 g-dw m(-2) day(-1). The specific growth rate reached a maximum of 0.41 day(-1) when the light intensity per cell was 7.9 mu E g-dw(-1) s(-1). As the light intensity per cell decreased with increasing cell density, E-k decreased gradually during the first half of the culture period. Interpretation : Chlorella vulgaris in this study had the ability to acclimate to shade conditions during high-cell-density cultivation, however, the photosynthetic efficiency decreased. High transformation efficiency of light energy for photosynthesis in shade-acclimated cells will help to exploit the mass culture of microalgae.