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

Zhen Zhu,Jing Tian,Xupeng Cao,Huijiao Cao,Junfeng Rong,Xu Li

doi:10.3389/fbioe.2020.603513

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 Chlamydomonas reinhardtii, 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), C. reinhardtii 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 Fv/Fm and Fv’/Fm’ and pH of culture, enhanced Calvin cycle by overexpressed cGAPDH promoted the carbon conversion and subsequent energy storage compounds accumulation. C. reinhardtii P3-GAPDH strain showed the potential as a good chassis with high carbon conversion ability.

Highlights

The green algae Chlamydomonas reinhardtii is a model organism that has been systematically studied for more than 50 years (Fields et al, 2018)
There was no significant difference in the growth during the first 2 days, while P3-GAPDH showed a clear step like day-night change pattern
P3-GAPDH kept growing to 60 h and its maximum optical density (OD) reached 6.37, which increased more than 50% than that of wild type (WT)

Summary

Introduction

The green algae Chlamydomonas reinhardtii is a model organism that has been systematically studied for more than 50 years (Fields et al, 2018). It has the most abundant physiological and biological information among microalgae with well-annotated genome information, and its genome of chloroplasts and mitochondria has been sequenced (Harris, 2001). As a single cell photosynthetic organism, C. reinhardtii provides a platform for the production of a wide range of complex proteins, pigments, and energy storage compounds, and is increasingly recognized as a cheap, scalable, and safe “cell factory” of high-value products as well as bioenergy (Carrera Pacheco et al, 2018). On the bioenergy and carbon sequestration aspect, C. reinhardtii has been investigated on the mechanism and application in hydrogen production (Degrenne et al, 2010; Scoma et al, 2012; Chen et al, 2014), biodiesel production (Fan and Zheng, 2017; Yang et al, 2018) and wastewater treatment (Faraloni et al, 2011), etc

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Conclusion