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

ABSTRACT: Cultivation of photosynthetic microbes under elevated CO2 is widely used in biotechnology to enhance growth. However, very high CO2 levels inhibit growth for reasons that are not always clear. We established a method that allowed cultivation under different CO2 concentrations and controlled pH to study the cyanobacterium Synechococcus sp. PCC 7002. Growth rates, cell composition, and transcriptomic profiles were investigated under limiting (0.04%), optimal (1-4%), and inhibitory high (15-30%) gas phase CO2 contents, while maintaining pH approx. 7.5. At intermediate light (200 µmol /m2 /s), the growth rate at 30% CO2 was approx. 45% of that under optimal conditions. 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)

ORGANISM(S): Picosynechococcus sp. PCC 7002

PROVIDER: GSE324819 | GEO | 2026/03/18

REPOSITORIES: GEO