Exploration of a cultivation strategy to improve eicosapentaenoic acid (EPA) production and growth of a Korean strain of Nannochloropsis oceanica cultivated under different light sources

Abstract

To propose a strategy for the commercial cultivation of a Korean strain of Nannochloropsis oceanica, the growth, fatty acid content and bacterial community of N. oceanica cultures exposed to different light sources were investigated. Significant growth of N. oceanica cultured under blue (450 nm), red (620 nm) and white (cool-white fluorescent; control) light was observed, whereas growth with relatively low densities was observed in N. oceanica cultured under purple (415 nm) and yellow (592 nm) light. Cells cultured under white and blue light began growing again at day 26, after experiencing stationary phases for 7 days, indicating that day 26 may be a switching point for the growth trajectory in batch culture of N. oceanica. White light also produced the highest biomass of N. oceanica, followed by blue, red, and yellow light. These results indicate that blue and red light, excluding the white light characterized by a wide spectral band, can ensure a high growth rate and biomass of a Korean strain of N. oceanica. With respect to fatty acid content, eicosapentaenoic acid (EPA) was the most dominant under the yellow and red light with N. oceanica exhibiting relatively low biomass dry weight and growth rates. In bacterial communities in N. oceanica cultures exposed to different light sources, the genus Roseovarius appeared to promote the growth of N. oceanica. Based on the results of this study, the most advantageous EPA production system for a Korean strain of N. oceanica initially uses white or blue light to produce the desired cell concentration and rapid growth, then switches to red or yellow light to enhance EPA content. This two-phase cultivation approach offers a viable pathway for large-scale EPA production from native strains, with potential application in nutraceutical or aquaculture industries.

Keywords: Bacteria; Batch culture; Growth; LED; Lipid.

Fig. 1

Image of cultivation of Nannochloropsis oceanica (LIMS-PS-0093) in an incubator with LEDs lights. A Purple light (415 nm); B blue light (450 nm); C yellow light (592 nm); D red light (620 nm)

Fig. 2

Growth curve (A) and maximum cell density (B) of Nannochloropsis oceanica (LIMS-PS-0093) exposed to different light sources

Fig. 3

Fatty acid content in Nannochloropsis oceanica (LIMS-PS-0093) cultures exposed to different light sources

Fig. 4

Clustering heatmap based on Pearson correlation coefficients, illustrating the similarity between bacterial communities associated with Nannochloropsis oceanica (LIMS-PS-0093) cultured under different light sources. The color intensity represents the relative abundance of bacterial taxa, with darker shades indicating higher abundance. The hierarchical clustering dendrogram at the top groups samples based on bacterial community composition, highlighting differences and similarities across light treatments (purple light: 415 nm, blue light: 450 nm, yellow light: 592 nm, red light: 620 nm, and control)

Fig. 5

Illustration of a cultivation strategy to improve the growth and eicosapentaenoic acid (EPA) production of a Korean strain of Nannochloropsis oceanica (LIMS-PS-0093)