(401f) Stress Induced Production of Canthaxanthin From a Novel Strain of Chlorella Isolated From the Sahara Desert

Carotenoids are high-valued anti-oxidants with application in the aquaculture, nutraceutical and cosmetic industries. The production of these compounds can often be induced in algal cell cultures by the application of an environmental stress, such as nutrient depletion or oxidative stress caused by oversaturation of the photosynthetic apparatus. In this study, we characterized the carotenoid production response of a new microalgal strain, Chlorella sp. strain MT1, which was isolated from the Sahara desert of Algeria. A baseline metabolic stress was imposed by using nitrate starvation and 10 g L^-1 NaCl. Because this strain was isolated from an environment of high solar intensity, it was hypothesized that this strain would possess efficient mechanisms for producing photoprotective pigments, such as secondary carotenoids, so varying light intensities (100, 300, 600 and 900 µE m^-2 s^-1) were applied to determine the effect of illumination stress on carotenogenesis.

It was determined that canthaxanthin was the main secondary carotenoid accumulated and that light intensities had an important influence on the rate of canthaxanthin accumulation, which reached 3.92 µg mL^-1 in the cultures grown under a light intensity of 600 μE m^-2 s^-1 compared to 1.2 µg mL^-1 in the culture grown under a light intensity of 100 μE m^-2 s^-1. The production of canthaxanthin was higher under higher light intensity up to a certain threshold, above which the production was diminished due to overstressing of the cultures. The disappearance of chlorophyll and the overproduction of lipids were commensurate with the production of canthaxanthin. When cultures were transferred from the nitrate and NaCl media into fresh media which did not impose the baseline metabolic stress, the cultures recovered and the process of carotenogenesis and chlorophyll reduction was reversed, and the cultures returned to their normal state.

Our results represent a step in the research for algal strains suitable for large-scale secondary carotenoid production. The selected strain showed a fast growth, good potential for production and fast induction of carotenoid production as well as a fast recovery when stress conditions were removed. This opens the possibility to use a semi-continuous, two-state cultivation process to alternatively increase biomass and carotenoids at the industrial scale. Specifically, cultures would be grown in low-saline, nutrient replete medium until high cell densities and nitrate starvation are achieved, at which time NaCl would be added to rapidly induce carotenogenesis. Cells would then be harvested and the make-up media would consist of NaCl-free, nutrient replete medium to re-induce the growth phase.