Enhanced carbon dioxide bio-fixation and protein production of Chlorella pyrenoidosa through a highly efficient sequential heterotrophic and photoautotrophic culture strategy

Abstract

Chlorella pyrenoidosa is one of the most promising microalgae for protein production with carbon dioxide (CO₂) bio-fixation. However, the high production cost and low production capability under traditional photoautotrophic culture mode had severely limited its application. Here, a highly efficient sequential heterotrophic and photoautotrophic cultivation strategy was established. Firstly, the heterotrophic seeds culture conditions were optimized with glucose as the carbon source and 1 g L⁻¹ of yeast extract was selected as a useful stimulus to boost cell growth. Then, the heterotrophic cells were transferred to photoautotrophic conditions directly and cultured under varied concentrations of CO₂. Moreover, 8 % (v/v) of CO₂, high light and high initial cell density were found to be beneficial for cell growth and CO₂ sequestration. Finally, different initial nitrogen concentrations and nitrogen feeding strategies were evaluated to increase the protein content to 62.69 % of dry biomass. These results provide feasible strategies for efficient CO₂ sequestration and protein production jointly in C. pyrenoidosa.