Abstract
Batch cultures of a microalga, Haematococcus pluvialis, were studied under various trophic conditions with addition of acetate as a carbon source and/or light irradiation. Under the mixotrophic condition (acetate + light), the morphological change from a growth flagellated cell to a resting cyst cell and the astaxanthin production occurred. The effects of the initial acetate concentration and the light intensity on cell growth and astaxanthin production were investigated. The appropriate culture condition for growth of flagellated cells was different from that for astaxanthin production of cyst cells. A two-stage culture system for the continuous astaxanthin production was constructed by connecting two reactors for growth and production in series. The subcultured cells were inoculated to the growth reactor at the start of the operation. The fresh medium with 1.2 g/dm3 acetate was continuously supplied to the reactor and the medium containing the cells from the growth reactor was fed to the production reactor. The light intensity in the growth and production reactors was 2300 and 4600 lux, respectively and the acetate of 0.12 g was added every day to the production reactor. Most of cells in the effluent from the growth reactor were flagellated ones, while those in the production reactor were cyst ones. The morphological change occurred in the production reactor. The astaxanthin concentration in the effluent from the growth reactor was almost zero, whereas that in the effluent from the production reactor was maintained at high value. This system permitted to continuously produce the cyst cells with high astaxanthin content.
