Light absorption and growth response of Dunaliella under different light qualities

Abstract

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 (μ) 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 μ (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 O2 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.