Photoautotrophic Production of Eicosapentaenoic Acid (EPA) with Nannochloropsis oceanica Under Dynamic Climate Simulations

Abstract

Marine microalgae from the genus Nannochloropsis are promising candidates for the photoautotrophic production of eicosapentaenoic acid (EPA, C20:5), a polyunsaturated fatty acid known for its numerous health benefits. A recent study demonstrated that Microchloropsis salina can accumulate high amounts of EPA when cultivated in flat-plate gas-lift photobioreactors. This study aimed to characterize an alternative strain, Nannochloropsis oceanica, and compare its biomass and EPA productivity to M. salina. Applying simulated dynamic climate conditions of a repeated sunny summer day in Eastern Australia, N. oceanica was cultivated in LED-illuminated flat-plate gas-lift photobioreactors. The results showed significantly higher biomass growth and EPA contents compared to M. salina. An EPA productivity of 33.0 ± 0.6 mg_EPA L⁻¹ d⁻¹ has been achieved in batch processes with N. oceanica. Scaling up the photoautotrophic process to 8 m² thin-layer cascade photobioreactors resulted in doubled concentrations of N. oceanica biomass compared to laboratory-scale batch processes. This improvement was likely due to the reduced fluid layer depth, which enhanced light availability to the microalgal cells. Using urea instead of nitrate as a nitrogen source further improved the EPA production of N. oceanica in thin-layer cascade photobioreactors, achieving CDW concentrations of up to 17.7 g L⁻¹ and thus a high EPA concentration of 843 mg L⁻¹. These findings highlight N. oceanica as an alternative to M. salina for sustainable EPA production, offering potential for further industrial applications.