Gibberellin Promotes Cell Growth and Induces Changes in Fatty Acid Biosynthesis and Upregulates Fatty Acid Biosynthetic Genes in Chlorella vulgaris UMT-M1

Microalgae lipids and oils are potential candidates for renewable biofuels and nutritional inventions. Recent studies from our lab have shown that two plant hormones, auxin and jasmonic acid, influence microalgae growth and fatty acid accumulation. Therefore, in this study, a high oil-producing strain Chlorella vulgaris UMT-M1 was selected for hormonal study using gibberellin (GA). Exogenous GA(3) was applied to early stationary culture of C. vulgaris UMT-M1. Results showed that GA(3) gradually increases the cell density of C. vulgaris to up to 42% on days after treatment (DAT)-8 and also capable of delaying the algal senescence. However, the increment in cell density did not enhance the total oil production albeit transient modification of fatty acid compositions was observed for saturated (SFA) and polyunsaturated (PUFA) fatty acids. This illustrates that GA(3) only promotes cell division and growth but not the oil accumulation. In addition, application of GA(3) in culture medium was shown to promote transient increment of palmitic (C16:0) and stearic (C18:0) acids from DAT-4 to DAT-6 and these changes are correlated with the expression of -ketoacyl ACP synthase I (KAS I) gene.