A Carbon Fixation Enhanced Chlamydomonas reinhardtii Strain for Achieving the Double-Win Between Growth and Biofuel Production Under Non-stressed Conditions

Abstract

The stressed cultivations are widely used in microalgae R&D for the biofuel production with the repress on growth to a certain degree, which limits the overall productivity. The balance between the growth and energy storage compounds accumulation is a target needing the combination of both strain selection or construction and culture optimization. Here, an engineered strain of <i>Chlamydomonas reinhardtii</i>, in which the chloroplast type glyceraldehyde-3-phosphate dehydrogenase (cGAPDH) was overexpressed and named as P3-GAPDH, was cultured on the Algal Station platform. Compared with wild type (WT), <i>C. reinhardtii</i> CC137c, in Tris-acetate-phosphate (TAP) medium, the highest density of WT and P3-GAPDH were 1.23 ± 0.13 and 1.74 ± 0.09 g L^-1 within 96 h, and the maximum biomass productivity was 24.30 ± 1.65 and 28.54 ± 1.43 mg L^-1 h^-1, respectively. In terms of the energy storage compounds, both carbohydrate and fatty acids content doubled in P3-GAPDH, from 0.13 ± 0.02 to 0.26 ± 0.04 g L^-1 for carbohydrate and from 0.08 ± 0.01 to 0.16 ± 0.01 g L^-1 for fatty acids, among which poly unsaturated fatty acids increased by 65.8%. Together with the continuous monitor of the chlorophyll fluorescence dynamics parameters <i>F</i> _v/<i>F</i> _m and <i>F</i> _v'/<i>F</i> _m' and pH of culture, enhanced Calvin cycle by overexpressed cGAPDH promoted the carbon conversion and subsequent energy storage compounds accumulation. <i>C. reinhardtii</i> P3-GAPDH strain showed the potential as a good chassis with high carbon conversion ability.