Study of carbon fixation and carbon partitioning of evolved Chlorella sp.'s strain under different carbon dioxide conditions

Algal biotechnology is a powerful tool for CO2 fixation. Rapid CO2 fixation and carbon partitioning are both important questions in the field of algal biotechnology. Adaptive laboratory evolution has been applied for improving the tolerance of microalgae to high concentration of CO2. A new strategy should be proposed to improve the CO2 fixation capacity and efficiency of ALE under non-stress conditions. An evolved strain, AE1, was obtained after 31 cycles (>157 generations) of adaptive evolution under 1% CO2 condition. The growth profiles and carbon partitioning were investigated for the evolved strain under 1%, 10% and 30% CO2 conditions. It was confirmed that AE1 could tolerate 10% CO2 but 30% CO2 inhibited the growth of AE1. Increasing CO2 concentration led to the increase of total protein contents and decrease of total lipid contents while the carbohydrate contents were not significantly varied at day 11. The biomass components and free fatty acids in starting strain, AE1 and AE10 evolved strain under 10% CO2 conditions were investigated. It was indicated that the metabolic phenotype of AE1 was different to those of starting strain and AE10 based on principal component analysis. It is also proved that the selection of environmental stress and strategy in adaptive evolution is very essential. The current study presents novel information of CO2 fixation and carbon partitioning of microalgae. It is confirmed that ALE could improve the CO2 fixation capacity of microalgae and it is helpful to establish new approach for carbon neutrality.