Light absorption and growth response of Dunaliella under different light qualities

Dunaliella sp. (formerly D. salina MACC/C43) was batch-cultured under blue (BL), red (RL), or white light (WL) provided by light-emitting diodes (LED) and white light provided by fluorescent lamps (WF), respectively, to assess growth characteristic. Growth under blue light coupled with red light (BL + RL) was also measured and compared with that under BL, WL, and RL, respectively, in a laboratory-scale photobioreactor. Algae under monochromatic blue light had the highest specific growth rate (mu) with a value of 0.51 day(-1), followed by WF (0.49 day(-1)), WL (0.47 day(-1)), and RL (0.44 day(-1)). Red light significantly enhanced Chl a and carotenoid contents, with values of 20.1 and 9.6 pg cell(-1), respectively. BL + RL increased the mu (0.20 day(-1)) compared to those rates under pure BL or RL ranging from 0.17 to 0.18 day(-1), in batch culture for 14 days using a photobioreactor with 3.2 L working volume. Cells absorb more photons for photosynthesis in the blue band. Mean extinction coefficient calculated based on the modified Lambert-Bill law at the blue light region (430-480 nm) was 0.885 cm(-1), which is 22, 11, and 15% higher than that of the red light region (630-700 nm), green light region (500-560 nm), and photosynthetically active radiation region (400-700 nm), respectively. Blue light also improved the initial slope and the maximum O-2 production rate in a photosynthesis-irradiance curve, whereas it lowered the compensation irradiance and dark respiration rate. The photochemistry of photosystem II also displayed its optimal performance under BL. LEDs are a suitable light source for Dunaliella sp. growth, and BL + RL promotes rapid division of algal cells.