Photosynthetic accumulation of carbon storage compounds under CO2 enrichment by the thermophilic cyanobacterium Thermosynechococcus elongatus

The growth characteristics of Thermosynechococcus elongatus on elevated CO₂ were studied in a photobioreactor. Cultures were able to grow on up to 20% CO₂. The maximum productivity and CO₂ fixation rates were 0.09 ± 0.01 and 0.17 ± 0.01 mg ml⁻¹ day⁻¹, respectively, for cultures grown on 20% CO₂. Three major carbon pools--lipids, polyhydroxybutyrates (PHBs), and glycogen--were measured. These carbon stores accounted for 50% of the total biomass carbon in cultures grown on atmospheric CO₂ (no supplemental CO₂), but only accounted for 30% of the total biomass carbon in cultures grown on 5-20% CO₂. Lipid content was approximately 20% (w/w) under all experimental conditions, while PHB content reached 14.5% (w/w) in cultures grown on atmospheric CO₂ and decreased to approximately 2.0% (w/w) at 5-20% CO₂. Glycogen levels did not vary significantly and remained about 1.4% (w/w) under all test conditions. The maximum amount of CO₂ sequestered over the course of the nine-day chemostat experiment was 1.15 g l⁻¹ in cultures grown on 20% CO₂.