Biofuel production from microalgae has attracted much attention as a promising route for a sustainable energy supply. The development of large-scale cultivation methods for microalgae is still a challenging task, since there is difficulty in microalgal harvesting from culture medium due to small size of the microalgal cells. In addition, since lipid accumulation in many microalgae is generally promoted by nutrient deprivation, large-scale equipment for removing nutrients such as nitrogen is required. To solve these issues, we are developing a novel culture method of microalgae for lipid production using encapsulation technique with beads of alginate hydrogel. As microalgae cells, Chlamydomonas debaryana (C. debaryana) was used in this study, which massively accumulate lipid in the stationary growth phase without nutrient deprivation. In this study, structure, cell proliferation and lipid accumulation of encapsulated C. debaryana cells in the alginate hydrogel were investigated. C. debaryana cells were encapsulated into the beads of alginate hydrogel with 3 mm in diameter by dropping a solution of sodium alginate containing C. debaryana cells into CaCl2 solution. After the cells were grown in the alginate hydrogel for six days, the encapsulated C. debaryana cells were extracted by dissolving the alginate hydrogel using EDTA solution, followed by staining with BODIPY dye to observe neutral lipid accumulation in the cells. Free C. debaryana dispersed as single cells in culture medium. In contrast, the encapsulated C. debaryana formed spherical cell aggregates in the alginate hydrogel after cell growth. Interestingly, both lipid accumulation and cell growth rates of the encapsulated C. debaryana in the hydrogels were larger than those dispersed as single cells. From these results, encapsulation technique using the alginate hydrogel is expected to be a new approach to develop large-scale cultivation methods for microalgae.

Spherical aggregation of microalgae with acceleration of cell growth and lipid accumulation by encapsulation in hydrogels

255th National Meeting (2018)

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