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 (OD₆₈₀). 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. [ABSTRACT FROM AUTHOR]