Morphological Change Rule In The Green Alga Haematococcus Pluvialis Cultures And Stimulating Factors

Due to its high antioxidant activity, astaxanthin has been widely applied in food, cosmetics and pharmaceutical industries. As the richest source of natural astaxanthin, microalga Haematococcus pluvialis has been paid more attentions. However, the alga has a complex life cycle with a variety of cell morphology. And algal cells are sensitive to environmental changes during the time of culture, thus cell morphology is greatly affected by the culture condition changes. In particular, different cell shapes have different physiological-biochemical characteristics. Improper changes in cell morphology may lead to low growth rate or even growth retardation, which limits its large-scale production. Therefore, cell morphological changes were observed in the process of cultivation and under different stimulating factors. With compositional analyses and microscopic structure observation, its change rule was sought, and the relationship of cell growth, cell morphological transformation and astaxanthin accumulation with the environmental change were also revealed. Main conclusions were the following:(1) Green motile cells, green non-motile cells, akinetes were the best type for cell reproduction, biomass production and astaxanthin accumulation, respectively.(2) Heterotrophy and phototrophy were the second best nutritional mode for cell growth after the mixotrophy. And mixotrophy helped to maintain the vegetative cells for a long time. Phototrophic induction, compared with other nutritional modes, speeded up the process from vegetative cells to cyst cells. Moreover, continuous CO2 met the requirements of carbon during photoinduction, and intracellular astaxanthin content was accounted for 4.13% of the cell dry weight and increased by 22.37% compared with no carbon dioxide.(3) ZYJS-1804 was one of the best plant hormones for the growth and astaxanthin production of H.pluvialis, and its optimal concentration was 0.005,0.5 mg/L, respectively. Low concentration of 2,4-D (0.005 mg/L2,4-D) increased by 63.49%,22.59%,38.36% for cell number, chlorophyll content per cell and chloroplast size, respectively. Astaxanthin content per cell and oil droplet size increased at a high concentration of 2,4-D (0.5 mg/L 2, 4-D). Two different concentrations of 2,4-D were used during two stages to obtain high quantity of biomass and astaxanthin.(4) The daytime temperature of 28 ℃ and the night temperature below 28 ℃ were optimal for achieving high biomass and astaxanthin content, respectively. Subsequently, the outdoor culture strategy was improved and could increase the net biomass and astaxanthin productivities by 5.0 and 2.9-fold as compared to the former strategy.This study will provide fundamental basis for the changes of cell morphology in a direction conducive to growth and astaxanthin bioaccumulation, and will give helps to improve the production of astaxanthin, to reduce production costs, and to accelerate the process of industrialization of astaxanthin from H. pluvialis.