Simultaneous photoautotrophic production of DHA and EPA by Tisochrysis lutea and Microchloropsis salina in co-culture

Abstract

Marine microalgae have received much attention as a sustainable source of the two health beneficial omega-3-fatty acids docosahexaenoic acid (DHA, C22:6) and eicosapentaenoic acid (EPA, C20:5). However, photoautotrophic monocultures of microalgae can only produce either DHA or EPA enriched biomass. An alternative may be the photoautotrophic co-cultivation of Tisochrysis lutea as DHA-producer with Microchloropsis salina for simultaneous EPA production to obtain EPA- and DHA-rich microalgae biomass in a nutritionally balanced ratio. Photoautotrophic co-cultivation processes of T. lutea and M. salina were studied, applying scalable and fully controlled lab-scale gas-lift flat-plate photobioreactors with LED illumination for dynamic climate simulation of a repeated sunny summer day in Australia [day–night cycles of incident light (PAR) and temperature]. Monocultures of both marine microalgae were used as reference batch processes. Differences in the autofluorescence of both microalgae enabled the individual measurement, of cell distributions in co-culture, by flow cytometry. The co-cultivation of T. lutea and M. salina in artificial sea water with an inoculation ratio of 1:3 resulted in a balanced biomass production of both microalgae simultaneously with a DHA:EPA ratio of almost 1:1 (26 mgDHA gCDW−1, and 23 mgEPA gCDW−1, respectively) at harvest after depletion of the initially added fertilizer. Surprisingly, more microalgae biomass was produced within 8 days in co-cultivation with an increase in the cell dry weight (CDW) concentration by 31%, compared to the monocultures with the same amount of light and fertilizer. What is more, DHA-content of the microalgae biomass was enhanced by 33% in the co-culture, whereas EPA-content remained unchanged compared to the monocultures. Graphical Abstract

Driving into the Factory of Docosahexaenoic Acid (DHA), Microalgae

“…The co-cultivation of microalgae species has been explored as a strategy for simultaneous production of EPA and DHA. Thurn, Stock [83] studied the photoautotrophic co-cultivation of Tisochrysis lutea and Microchloropsis salina, which resulted in the production of appropriate balance of EPA and DHA in the studied microalgae. Overall, metabolic engineering of microalgae holds great potential for enhancing DHA production.…”

LED Illumination Modules Enable Automated Photoautotrophic Cultivation of Microalgae in Parallel Milliliter-Scale Stirred-Tank Bioreactors

“…The growth of Microchloropsis salina (M. salina, SAG 40.85) obtained from the Culture Collection of Algae at the University of Göttingen, Germany, was investigated in miniaturized stirred-tank bioreactors. M. salina is a compelling microalgae because of the potential of its lipid production as sustainable feedstock for biofuels [57], its photoautotrophic eicosapentaenoic acid (EPA) production [58], and its being a suitable model microalgae because of its known light-dependent growth kinetics [30]. The culture was kept in shaking flasks at room temperature and ambient light conditions until the precultures were prepared (20 mL inoculum and 180 mL ASW).…”

“…All results showed either directly measured or correlated cuvette OD 750 . OD measurement at 750 nm is an established method for growth monitoring of microalgae [16,57,58].…”

Photoautotrophic Production of Docosahexaenoic Acid- and Eicosapentaenoic Acid-Enriched Biomass by Co-Culturing Golden-Brown and Green Microalgae

“…The phototrophic cocultivation of the golden-brown microalgae T. lutea (DHA producer) with the green microalgae Microchloropsis salina (EPA producer) was recently studied in a flat-plate gas lift photobioreactor with LED illumination. A balanced DHA-to-EPA ratio (26 ± 2 mg DHA g CDW and 23 ± 4 mg EPA g CDW ) was achieved after a process time of 8 days applying a dynamic climate simulation of a repeated summer day in Australia [30]. Furthermore, the biomass and DHA areal productivity in co-culture increased by 31% and 33%, respectively, compared to two monocultures of the same microalgae strains.…”