Cold and dark treatments induce omega-3 fatty acid and carotenoid production in Nannochloropsis oceanica

Nannochloropsis is one of the most-studied microalgae because of its high eicosapentaenoic acid (EPA) content and high-value carotenoids. However, during large-scale farming, decreased EPA productivity of Nannochloropsis oceanica BR2 was observed when cultured during the summer season (≥30 °C). We hypothesized that short low temperature treatments and membrane biosynthesis during reduced light exposure may increase EPA yields. Thus, we investigated the effect of 3-day cold or dark treatments on N. oceanica BR2 nutritional composition by measuring fatty acid and carotenoid profiles. Indeed, treated samples contained increased levels of polyunsaturated fatty acids including EPA and carotenoids violaxanthin and zeaxanthin. Tunnelling electron microscopy showed increased an chloroplast size and an increased number of thylakoid membranes in treated samples, visualizing how cells adapt to these environmental changes. The present study provides a practical strategy on how heat-stressed Nannochloropsis cultures can be subjected to short 3-day treatments before harvesting to enable high-value biomass production.