Production of lutein, and polyunsaturated fatty acids by the acidophilic eukaryotic microalga Coccomyxa onubensis under abiotic stress by salt or ultraviolet light.

In this study, the effect of abiotic stress on the acidophilic eukaryotic microalga, Coccomyxa onubensis, was analyzed for the production of lutein and PUFAs (polyunsaturated fatty acids). It grows autotrophically at a pH of 2.5. It showed a growth rate of 0.30 d-1, and produced approximately 122.50 mg·L-1·d-1 biomass, containing lipids (300.39 mg g-1dw), lutein (5.30 mg g-1dw), and ß-carotene (1.20 mg g-1dw). The fatty acid methyl ester (FAME) fraction was 89.70 mg g-1dw with abundant palmitic acid (28.70%) and linoleic acid (37.80%). The addition of 100 mM NaCl improved the growth rate (0.54 d-1), biomass productivity (243.75 mg·L-1·d-1), and lipids accumulation (416.16 mg g-1dw). The microalga showed a lutein content of 6.70 mg g-1dw and FAME fraction of 118.90 mg g-1dw; 68% of the FAMEs were PUFAs. However, when 200-500 mM salt was added, its growth was inhibited but there was a significant induction of lutein (up to 7.80 mg g-1dw). Under continuous illumination with PAR (photosynthetically active radiations) +UVA (ultraviolet A, 8.7 W m-2), C. onubensis showed a growth rate of 0.40 d-1, and produced 226.3 mg·L-1·d-1 biomass, containing lipids, (487.26 mg g-1dw), lutein (7.07 mg g-1dw), and FAMEs (232.9 mg g-1dw); 48.4% of the FAME were PUFAs. The illumination with PAR + UVB (ultraviolet B, 0.16 W m-2) was toxic for cells. These results indicate that C. onubensis biomass is suitable as a supplement for functional foods and/or source of high added value products.

IDENTIFICATION AND PHYSIOLOGICAL ASPECTS OF A NOVEL CAROTENOID-ENRICHED, METAL-RESISTANT MICROALGA ISOLATED FROM AN ACIDIC RIVER IN HUELVA (SPAIN)(1).

A heavy-metal-resistant, carotenoid-enriched novel unicellular microalga was isolated from an acidic river in Huelva, Spain. The isolated ribosomal 18S subunit rDNA sequence showed homology with known sequences from green microalgae, the closest sequence (98% homology) belonging to the genus Coccomyxa. The isolated microalga therefore was an up to now uncultured microalga. The microalga was isolated from Tinto River area (Huelva, Spain), an acidic river that exhibits very low pH (1.7-3.1) with high concentrations of sulfuric acid and heavy metals, including Fe, Cu, Mn, Ni, and Al. Electron micrographs show that the microalga contains a large chloroplast with a presence of lipid droplets, an increased number of starch bodies as well as electron-dense deposits and plastoglobules, the last observed only in iron-exposed cells. Unlike other acidophile microalgae, the isolated microalga showed high growth rates when cultivated photoautotrophycally (up to 0.6 d(-1) ) in a suitable culture medium prepared at our laboratory. The growth was shown to be iron dependent. When the microalga is grown in fluidized bed reactors, the high growth rates resulted in unexpectedly high productivities for being a microalga that naturally grows in acidic environments (0.32 g·L(-1) ·d(-1) ). The microalga also grows optimally on reduced carbon sources, including glucose and urea, and at an optimal temperature of 35°C. The alga pigment profile is particularly rich in carotenoids, especially lutein, suggesting that the microalga might have potential for antioxidant production, namely, xanthophylls.