Light and excessive CO2 uptake inhibit growth of Synechococcus sp. PCC 7002 under very high CO2 levels

Under low light (<100 µmol /m2 /s), growth was less inhibited by high CO2 than at higher light intensities. Pigmentation and photosynthesis likewise decreased under high CO2, except that carotenoids indicative of high-light stress increased. Transcriptome sequencing confirmed that the photosynthesis machinery was downregulated and stress responses were upregulated under high CO2.

Genetic knockdown of CO2 uptake (ndhF3 and ndhF4) or overexpression of a heterologous Na+/H+ antiporter (nhaS3) improved tolerance to high CO2, while knockdown of the CcmR transcriptional regulator reduced it. We conclude that the inhibiting species under very high inorganic carbon conditions was CO2, and not HCO3-, and that reduced light intensity or genetically suppressing active CO2 uptake improved the tolerance of Synechococcus to very high CO2 conditions.

This work provides a basis for cultivation under a very wide range of CO2 concentrations, thereby broadening the scope for metabolic manipulation and biotechnological applications of cyanobacteria. (Algal Research)