LC-PUFA-Enriched Oil Production by Microalgae: Accumulation of Lipid and Triacylglycerols Containing n-3 LC-PUFA Is Triggered by Nitrogen Limitation and Inorganic Carbon Availability in the Marine Haptophyte Pavlova lutheri

Abstract

In most microalgal species, triacyglycerols (TAG) contain mostly saturated and monounsaturated fatty acids, rather than PUFA, while PUFA-enriched oil is the form most desirable for dietary intake. The ability of some species to produce LC-PUFA-enriched oil is currently of specific interest. In this work, we investigated the role of sodium bicarbonate availability on lipid accumulation and n-3 LC-PUFA partitioning into TAG during batch cultivation of Pavlova lutheri. Maximum growth and nitrate uptake exhibit an optimum concentration and threshold tolerance to bicarbonate addition (~9 mM) above which both parameters decreased. Nonetheless, the transient highest cellular lipid and TAG contents were obtained at 18 mM bicarbonate, immediately after combined alkaline pH stress and nitrate depletion (day nine), while oil body and TAG accumulation were highly repressed with low carbon supply (2 mM). Despite decreases in the proportions of EPA and DHA, maximum volumetric and cellular EPA and DHA contents were obtained at this stage due to accumulation of TAG containing EPA/DHA. TAG accounted for 74% of the total fatty acid per cell, containing 55% and 67% of the overall cellular EPA and DHA contents, respectively. These results clearly demonstrate that inorganic carbon availability and elevated pH represent two limiting factors for lipid and TAG accumulation, as well as n-3 LC-PUFA partitioning into TAG, under nutrient-depleted P. lutheri cultures.

Bicarbonate supplementation enhanced biofuel production potential as well as nutritional stress mitigation in the microalgae Scenedesmus sp. CCNM 1077

“…CCNM 1077. Lower nutrient consumption under high bicarbonate supplementation might be due to increase in pH of the growth medium since it has been known that many salts of the marine culture medium gets precipitated and become unavailable for consumption by microalgae (Guihéneuf and Stengel, 2013). …”

“…However, only few researchers have studied the effects of bicarbonate addition under nitrate limited growth conditions (White et al, 2013;Guihéneuf and Stengel, 2013) and there are no reports on effects of bicarbonate addition under phosphate or combined nitrate phosphate stress conditions in microalgae. Total lipid content of microalgae Scenedesmus sp.…”

“…There was no significant difference (p < 0.05) in total lipid content of cells cultivated with 0.6 g/L (20.91 ± 0.31%) and 0.9 g/L (20.89 ± 0.35%) sodium bicarbonate. Guihéneuf and Stengel (2013) showed that under supply of inorganic carbon in the form of sodium bicarbonate microalgae Pavlova lutheri produce high amount of LC-PUFA rich TAGs which are mainly generated from de novo synthesis rather than membrane remodeling. In the present study, no significant difference in lipid content was observed in 1.2 g/L (19.36 ± 0.23%) and 1.5 g/L (19.07 ± 0.29%) sodium bicarbonate supplemented cultures.…”

Cellular Cycling, Carbon Utilization, and Photosynthetic Oxygen Production during Bicarbonate-Induced Triacylglycerol Accumulation in a Scenedesmus sp.

“…The use of sodium bicarbonate to enhance TAG accumulation has been demonstrated in both freshwater and marine chlorophytes as well as diatoms [15,16,20,44,45], and its use offers inherent advantages. Gaseous CO 2 is costly to store and transport, whereas bicarbonate salts can easily be transported to algal facilities and stored until needed.…”

Growth phase significantly decreases the DHA-to-EPA ratio in marine microalgae

“…For example, when cultured under nitrate or silicate starvation, TAGs accumulated up to 14-18 % of total dry weight in the marine diatoms Thalassiosira pseudonana and Phaeodactylum tricornutum (Yu et al 2009). Although most of the LC-PUFAs can be found in structural membrane lipids (Roessler 1990), LC-PUFAs could be partitioned to or deposited in TAGs during the stationary phase of growth (Khozin-Goldberg et al 2002;Tonon et al 2002;Guihéneuf and Stengel 2013). In three of the four species investigated by Tonon et al (2002) (Nannochloropsis oculata, T. pseudonana and Pavlova lutheri), this resulted in a higher cellular EPA content.…”