Effect of phosphorus and growth phases on the transcription levels of EPA biosynthesis genes in the diatom Phaeodactylum tricornutum

Polyunsaturated fatty acids (PUFAs) are essential in the animal diet, notably eicosapentaenoic and docosahexaenoic acids (EPA and DHA, respectively), and in recent years, microalgae like marine diatoms are being considered as an alternative source of PUFA. Therefore, this study evaluated the effect of three nitrogen/phosphorus (N/P) ratios (21/1, 14/1 and 7/1) and two growth phases (exponential and stationary) on both EPA concentration and gene transcript levels, four front-end desaturases and two elongases, involved in EPA biosynthesis of the microalgae Phaeodactylum tricornutum Bohlin. The experiment was carried out for 12 days, and the samples were assessed for growth and nutrient intake; in addition, qPCR was performed, as well as an analysis of fatty acids. Gene transcript levels were growth phase-dependent, and only two genes, PTD6 and PTD5A, were responsive to N/P ratios. EPA levels in P. tricornutum biomass were shown to be growth phase-dependent, with higher concentrations in the exponential phase (28.64% of total fatty acids), irrespective of N/P treatments. In at least one N/P ratio (21/1), the transcription of one gene, PTD5A, could be associated with EPA levels. Data from gene transcript levels and EPA concentrations, as well as the lack of some EPA intermediates, might indicate some type of regulatory steps between gene transcription and actual EPA biosynthesis.