Phytohormonal impacts on fatty acid profiles in Chlorella vulgaris Beijerinck: endogenous identification and exogenous application of cytokinins and abscisic acid

Chlorella vulgaris has a high lipid content with potential for biofuel application. With a rapid growth cycle and ease of culture, it is well suited for observing lipid profile changes and connecting this with phytohormone responses at a cellular level. The present study profiled C. vulgaris endogenous phytohormone levels in nutrient rich media and determined how exogenous phytohormone application affected its lipid metabolism. Endogenous phytohormone profiling using high-resolution liquid chromatography-tandem mass spectrometry revealed methylthiolated cytokinins as the most dominant cytokinin form produced. The impact of exogenous benzyladenine, trans -zeatin, 2-methylthio- trans -zeatin, and abscisic acid at three concentrations (10 –7 , 10 –6 and 10 –5 M) was assessed using daily growth monitoring via optical density (OD 680 ). Extraction and assessment of total lipid content followed the Soxhlet method, and fatty acid measurements of five fatty acids (α-linolenic, linoleic, palmitic, oleic, and stearic acids) was done using gas chromatography equipped with a flame ionization detector. Growth stimulation was the highest at 10 –6 M for all exogenous phytohormones except trans -zeatin, which was most effective at 10 –5 M. All exogenous treatments caused changes in fatty acid methyl ester (FAME) content, especially benzyladenine at 10 –6 M. For α-linolenic acid, the most significant change occurred with the addition of 10 –7 and 10 –6 M 2-methylthio- trans -zeatin, resulting in its increased production by 141% and 381%, respectively. This is the first report of 2-methylthio- trans -zeatin supplementation in microalgal cultures to date. The results presented suggest that using 2-methylthio- trans -zeatin exogenously can enhance α-linolenic acid production for pharmaceutical or industrial purposes.