Characterization of fatty acid and carotenoid production in an Acutodesmus microalga isolated from the Algerian Sahara

Microalgae are emerging as important cell factories for the production of various commercial products such as carotenoids and fatty acids (FA) and the potential still exists to convert algal lipids into biofuels. Indeed, several species of microalgae have already demonstrated the capacity to accumulate intracellular concentrations of over 50% lipids on a dry cell weight (DCW) basis under species-specific stresses such as nitrate or silicon limitation. An Acutodesmus microalga of the Scenedesmaceae family isolated from the Algerian Sahara was characterized for its ability to produce lipids, fatty acids (FA) and carotenoids under environmental stress conditions that should induce this production. Specifically, the combination of osmotic, nutritional and oxidative stress and the interactive effect of light intensity on lipid production and composition during batch growth were investigated. We also examined the recovery of the cell culture after the stress conditions were removed in order to study the feasibility of a reversible, and thus semi-continuous, cultivation process for the production of algal bioproducts. The FA produced by this strain isolated from an environment typified by extreme heat showed a lower degree of unsaturation than those of other Scenedesmus which have been isolated from cold or temperate water environments, with no unsaturated C16 FA and more than 92 % of the FA profile being comprised of FA with less than three unsaturated bonds. According to the degree of unsaturation and the cetane number, the FA profile from this strain is applicable to biofuel production. Under the highest lipid production conditions, the fatty acid profile in the present study has a stationary phase degree of unsaturation (DU, 97 ± 2) and predicted cetane number (CN, 55 ± 2), two measures of biodiesel quality, comparable to or better than all readily available vegetable oil sources except for palm. Lipogenesis and carotenogenesis were easily reversible upon removal of the stress. We determined that the principal carotenoid produced by our isolate was canthaxanthin. The production of secondary carotenoids was proportional to the lipid production suggesting that the primary role for secondary carotenogenesis in our isolate is to prevent peroxidation of the lipids within OB. Our results represent a step towards the development of strains suitable for biofuel production at the industrial scale