Enhanced growth and total fatty acid production of microalgae under various lighting conditions induced by flashing light.

Microalgae are gaining importance as a source of high-value bioproducts. However, data regarding optimization of algal productivity via variation of environmental factors are lacking. Here, we evaluated a novel lighting method for the enhancement of biomass and total fatty acid (TFA) productivities during algal cultivation. We cultivated six different algal strains (Chlorella vulgaris KCTC AG10002, Acutodesmus obliquus KGE18, Uronema sp. KGE03, Micractinium reisseri KGE19, Fragilaria sp., and Spirogyra sp.) under various lighting conditions-continuous light (CL), light-dark cycle (LD), and continuous dark (CD)-with or without additional flashing light. We monitored dry cell weight (DCW) and TFA concentrations during cultivation. For each algal strain, the growth rate showed markedly different responses to the various lighting modes. The growth rates of C. vulgaris KCTC AG10002 (1.34-fold DCW increase, LD with flash), A. obliquus KGE18 (5.16-fold DCW increase, LD with flash), Uronema sp. KGE03 (2.77-fold DCW increase, CL with flash), and M. reisseri KGE19 (1.52-fold DCW increase, CL with flash) markedly increased in response to flashing light. Additionally, in some algal strains cultivated under the LD mode, the flashing light treatment induced increased TFA concentrations (C. vulgaris, 1.19-fold increase; A. obliquus, 2.59-fold increase; and M. reisseri, 3.31-fold increase). Phytohormone analysis of M. reisseri revealed increases in growth rate and TFA concentrations, associated with phytohormone induction via flashing light (e.g. 2.93-fold increase in gibberellic acid); hence, flashing light can promote substantial alterations in algal metabolism.