The molecular mechanisms of Chlorella sp. responding to high CO2: A study based on comparative transcriptome analysis between strains with high- and low-CO2 tolerance

Abstract High CO2 acclimation for microalgae has attracted large research attention owing to the usefulness of microalgae in bio-sequestration of CO2 from the emission source. In this study, one high CO2 tolerant (LAMB 31) and non-tolerant (LAMB 122) Chlorella sp. strains were transferred from air to 40% CO2, during which four time points were chosen for comparative transcriptome analysis. Gene changes started in the lag phase (T1) of population growth with more genes (7889) upregulated in LAMB 31 than in LAMB 122 (1092). Further function enrichments indicated: In LAMB 31, up-regulation of genes in cyclic electron transportation, F-type ATPase and Calvin cycle were associated with the enhancement of carbon fixation abilities; upregulation of genes in phosphorylation together with V-ATPase, which contributed to cytoplasmatic pH stability; Lastly, enhancement of carbon metabolisms including TCA cycle and glycolysis accelerated the consumption of cellular organic carbon. Most of the genes in these pathways and processes showed downregulation in LAMB 122. This study disclosed the most complete transcriptional molecular mechanisms of Chlorella sp. responding to high CO2 by combining CO2 fixation, transportation, and metabolic processes. The results provided valuable genetic information for future screening and breeding of microalgae with high-CO2 tolerance for more efficient CO2 bio-sequestration.