A novel process for the production of Chromochloris zofingiensis through dark-induced multi-nuclei formation

Chromochloris zofingiensis is an astaxanthin- and lipid-producing green microalga. In this study, we examined the effect of transitioning cultures between light and dark conditions on biomass productivity. In general, cell proliferation was observed when cultures were transferred from dark heterotrophic conditions (12 d) to irradiated autotrophic conditions; these cells were multinucleated and showed rapid division. Specific growth rates of 1.85 and 0.36 d−1 were observed in heterotrophically precultured and autotrophically precultured cells, respectively. Under subsequent dark conditions, the autotrophically precultured cells became larger and the number of nuclei per cell increased from 1–2 to 6–12 within 8 d, indicating that the dark conditions blocked cytokinesis while allowing DNA replication through nuclear division. Our study also defined a relative nuclear division rate by comparing the specific growth rate of nuclei per cell with that of cell division. The unique coordination of multinucleated cells cultured in the dark and cellular division triggered by environmental light can improve the biomass productivity of this valuable alga. Our study reported the multinucleation mechanisms in C. zofingiensis which was accompanied by a rapid cellular division.