Production of lipids by Oleaginous Microalgae and Thraustochytrids
The main objective has been the production of lipids using oleaginous microorganisms (microalgae and thraustochytrids) as biological conversion tools of sugar streams. To maximize the sugar to lipid conversion the growth conditions for each species were optimized using commercial glucose as the carbon source. Specifically, the growth of two microalgal strains (Auxenochlorella protothecoides (AP) and Chlorella sorokiniana (CS)) was assessed using six different nitrogen sources (1.yeast extract, 2.corn steep liquor, 3.urea, 4.sodium nitrate, 5.ammonium sulfate, 6.ammonium nitrate). Using the nitrogen sources 1-4 which yielded higher lipids, the C/N ratio (5, 10, 20, 60) was screened. Finally, the maximum lipid yield was achieved using yeast extract and corn steep liquor at C/N 60. Both strains were grown mixotrophically at the optimal conditions at varying light intensities (50, 100, 200, 400 µmol/m2/s). However, the lipid yields were almost 1.7-fold lower compared to the heterotrophic cultivation. Thraustochytrids can grow under highly saline environments, therefore two strains (Schizochytrium sp. (S8) and Aurantiochytrium sp. T66 (pRA)) were grown under different salinity levels (0, 25, 50, 75, 100 %), using 20 g/L glucose and yeast extract (C/N 10), to identify the optimal (50 %; 9 ppt). Next, the C/N ratio (5 to 50) was screened and the optimal was found to be C/N 10. Using these optimal conditions, the glucose concentration was also tested (20 to 120 g/L) and the optimal was found to be 40 g/L for pRA and 60 g/L for S8. Corn steep liquor also proved to be a promising nitrogen source for the growth of thraustochytrids. Finally, to improve the process, all strains were cultivated in beechwood hydrolysate as a renewable glucose source together with corn steep liquor as an economical nitrogen source. An additional thraustochytrid strain (Aurantiochytrium limacinum (SR21)) was used in that step, as the previous growth optimization has already been reported.
- Microalgae can produce lipids up to 3.3 g/L which are rich in monounsaturated fatty acids (MUFAs) – good biodiesel properties.
- Thraustochytrids can produce lipids up to 13.6 g/L which are rich in polyunsaturated fatty acids (PUFAs) – good nutraceutical properties.
This project has received funding from the European Union’s Horizon 2020 research and innovation programme under Grant Agreement No. 101007130.