Exogenous ethanol induces cell giantism accompanied by enhanced accumulation of lipid and carbohydrates in Chlorella sorokiniana.

Ethanol has been reported as a supplementary substrate for microalgae cultivation, however, information about its effect on the morphology, growth and desired metabolites accumulation of Chlorella sorokiniana is limited. To bridge this gap, the effects of exogenous ethanol on C. sorokiniana was screened by providing 0.00, 0.0025, 0.025, 0.1 and 1% (v/v) ethanol. Results showed ethanol caused multifaceted effects. 0.0025% and 0.025% ethanol caused a small increase in cell volume, growth and photosystem II (PSII) function. In contrast, cell volume conspicuously increased and was up to 2.5-fold (63.5 µm3) and 3.6-fold (91.3 µm3) higher in the 0.1% and 1% ethanol treatment groups, respectively, compared with the control (25.1 µm3). 1% ethanol conspicuously reduced chlorophyll concentration, inhibited growth, damaged the photosynthetic apparatus and decreased PSII electron transport. Carbohydrate and lipid accumulation increased in the 0.1% (112.6±7.8 µg mL-1) and 1% (217.87±31.6 µg mL-1) ethanol by 1.6 and 50-fold, compared to the control (70.5±2.2 µg mL-1and 7.2±2.6 µg mL-1). The cell permeability also increased coinciding with the pronounced increse of reactive oxygen species, particularly in the 0.1 and 1% ethanol treatment groups. There were giant palmloid-like cells containing unequal and numerous daughter cells in the higher ethanol treatments, indicating the cell cycle has been altered through suppression of mother cell cytokinesis, which could serve as a protective function to overcome ethanol stress. The results suggest that ethanol has the potential to be used as an impotent substrate to induce lipid and carbohydrate accumulation in C. sorokiniana cultivation. [ABSTRACT FROM AUTHOR]