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

Abstract

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 phasedependent, 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.

Enhancement of Biomass Production of Diatom Nitzschia sp. S5 through Optimisation of Growth Medium Composition and Fed-Batch Cultivation

“…Silicon tends to polymerise, so the concentration of the assimilable silicon decreases. If the rate of consumption of the assimilable monomeric and dimeric form of silicon by diatom is higher than their generation by depolymerisation from silicon polymers [ 35 , 36 ], it could limit diatom growth, resulting in a decrease in specific growth rates, the concentration of biomass, and cell number at higher Si concentrations (1.5 and 2 mM). Some authors also observed an inhibitory effect in the presence of high silicon concentration [ 35 ].…”

Domoic Acid Oxidative Effects on the Microalgae Phaeodactylum tricornutum

“…Moreover, cells exposed to DA in the LAG phase of growth also exhibited a higher decrease in AH − content, as compared to cells in the EXP growth phase. The different behavior observed among the growth phases could be influenced by the diverse nutrient availability and metabolism in each phase, being more active in the EXP phase [ 51 , 52 ]. To assess the magnitude of the ability of the antioxidant defense network to control the oxidant effects of DA exposure in the cells in the three phases of development, damage markers should be evaluated in the future.…”

Biochemical and Molecular Aspects of Phosphorus Limitation in Diatoms and Their Relationship with Biomolecule Accumulation

“…Yongmanitchai and Ward [33] cultured P. tricornutum in Mann Myers medium and increased the P concentration from 2.5-fold to 5-fold higher than the control, and they found no significant differences in total biomass content among all the treatments. Recently, Lopes et al [34] cultured P. tricornutum in F/2 medium and increased the P concentration from 1.5-fold to 3-fold higher than the control, finding the same results as Yongmanitchai and Ward [33]. On the other hand, in studies carried out in Chaetoceros muelleri grown in F medium, P concentration was doubled compared to the control, and a higher content of dry biomass was found in the control treatment compared to the P excess treatment.…”

“…Another characteristic fatty acid is eicosapentaenoic acid (EPA), which can represent more than 10% of the total fatty acid profile of diatoms [132,138,139]. It has been widely reported in microalgae that culture phases and different abiotic factors, such as temperature, light, CO 2 supply and nutrient availability (such as P), influence the fatty acid content, and diatoms are not an exception [34,[140][141][142].…”

“…On the other hand, the effect of P excess on microalgae and its fatty acid profile has been little explored. Lopes et al [34] evaluated three P concentrations (76, 114 and 228 µM) and two growth phases (exponential and stationary) and their effect on the fatty acid profile in P. tricornutum cultured in F/2 medium. The results obtained in this study showed that even though the P concentration increased from 1.5-fold to 3-fold higher than the control treatment, no significant differences were detected in the content of fatty acids between the different P concentrations.…”