Abstract

Haematococcus pluvialis is a unicellular green microalga cultivated on a large scale as a natural source of astaxanthin, a ketocarotenoid of high commercial value due to its colorant and antioxidant properties. The aim of this study was to compare growth and total carotenoids among four strains of H. pluvialis isolated from different microhabitats in two geographical locations in Chile. Growth was carried out under autotrophic and mixotrophic conditions and under two photon flux densities (PFD) (20 and 85 μmol m-2s-1). Total carotenoid content was estimated on day 45. Most of the strains grew better under the autotrophic conditions; the highest exponential growth rates were exhibited at the high PFD in all the strains (ranging from 0.73 to 1.20 div day-1) with the exception of CCM-UDEC 023 which showed the same exponential growth rate with either PFD (0.73 div day-1). However, the cell density estimated on day 14 was higher at the low PFD in CCM-UDEC 022 and CCM-UDEC 023 (4.4 × 105 and 8.9 × 104 cells ml-1, respectively). The mixotrophic condition slightly improved the growth rate of the strain CCM-UDEC 021 at the high PFD (from 1.04 div day-1 at autotrophic condition to 1.25 and 1.14 div day-1 at 2mM and 10mM sodium acetate, respectively). The algal dry weight estimated on day 14 was not significantly correlated with the cell density, but it was, to a certain extent, related to the proportion and size of the different cell types quantified on that day. The strain with the highest dry weight at the end of the experimental period and under all the assayed conditions was CCM-UDEC 023. It was also the strain that produced the highest total carotenoid content under both autotrophic (5.6 mg l-1 and 95.6 pg cell-1 at the high PFD) and mixotrophic (with 2mM acetate) conditions (10.8 mg l-1 and 297 pg cell-1 at the high PFD). A high intraspecific variability in the physiological attributes analyzed existed among the strains under study. Even though the mixotrophic condition assayed did not substantially improve the growth rate of any strain, it did improve the total carotenoid yield in the strain CCM-UDEC 023.