Culture of 26 Haematococcus strains under autotrophic and mixotrophic conditions and astaxanthin production

In this study, 26 wild strains of Haematococcus spp. collected from different locations around the world were cultured in autotrophic medium (MES-volvox) or mixotrophic medium (MM2). The cell proliferation ability, biomass production (dry weight), and dead cell rate of each culture were measured to compare the astaxanthin synthesis ability. These strains could be grouped into a monophyletic group consisting of five clades by molecular phylogenetic analysis. They were found to consist of 20 strains of Haematococcus pluvialis, 4 strains of Haematococcus rubicundus, and 2 strains of Haematococcus rubens. Although there were clear differences in cell proliferation and astaxanthin synthesis ability among the strains, no specific characteristics were found for each clade as revealed by molecular phylogenetic analysis. Particularly, in MM2 medium, there were large differences among strains in the efficiencies of using acetic acid as a carbon source and amino acids as a nitrogen source. Carotenoid analysis by high-performance liquid chromatography (HPLC) revealed that the SCCAP K-0084 strain accumulated the most astaxanthin per dry weight under both autotrophic (MES-volvox) and mixotrophic (MM2) conditions.