Variation of fatty acid profile with solar cycle in outdoor chemostat culture ofIsochrysis galbana ALII-4

Abstract

Outdoor chemostat cultures of the marine microalgaIsochrysis galbana at constant dilution rate (0.034 h⁻¹ ) have been carried out under different weather conditions. Steady-state biomass concentrations were 1.61±0.03 kg m⁻³ in May and 0.95±0.04 kg m⁻³ in July, resulting in biomass output rates of 0.54 kg m⁻³ d⁻¹ and 0.32 kg m⁻³ d⁻¹ in May and July, respectively. Two patterns of daily variation with the solar cycle were observed in the fatty acid content. Saturated and mono-unsaturated fatty acids (16:0 and 16:1n7) show significant variation with the solar cycle, associated with short-term changes in environmental factors. Palmitic and palmitoleic acids are generated during daylight and consumed during the dark period. However, polyunsaturated fatty acids do not show a significant response to the solar cycle and their changes are associated with long-term variation in environmental factors. The maximum EPA productivity was obtained in May, 14.1 g m⁻³ d⁻¹, which is close to that found in the literature for indoor continuous cultures. Nonetheless, the outdoor EPA content (up to 2.61 % d.wt) was lower than the indoor EPA content from a previous study (5% d.wt).