(199g) Insights into the Industrial Growth of Cyanobacteria from a Model of the Carbon Dioxide Concentrating Mechanism

The direct production of fuels and chemicals from CO₂ using genetically engineered photosynthetic cyanobacteria would bypass much of the land, water, and transportation problems associated with biomass cultivation for traditional fermentation or catalytic conversion. However, current productivity of chemicals by these engineered cyanobacteria is too low to be economically feasible. The most troublesome bottleneck in cyanobacterial photosynthesis is the uptake of CO₂, the building block from which molecules of interest are synthesized. Therefore, a profitable and controllable industrial process for the production of small molecules by cyanobacteria must be assisted by the development of a platform organism capable of metabolizing a higher flux of CO₂ and able to efficiently convert that flux into desired chemicals. Modeling of cyanobacterial growth on both an intracellular and macroscopic level can be used to understand the mechanisms of CO₂-fixation and their implications in a large scale process.

The cyanobacterial carbon dioxide concentrating mechanism (CCM) comprises a system of structural proteins and enzymes that enable cyanobacteria to increase the local concentration of CO₂ around the carbon-fixing enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) by up to three orders of magnitude. This mechanism allows cyanobacterial growth in their native aqueous environment with low concentrations of CO₂. A quantitative model of this mechanism is described in this work and shows that the CCM is unnecessary for growth in media in equilibrium with a gas phase of 10% CO₂, a concentration readily available in abundant industrial flue gas. Because the proteins involved in the CCM are large, and therefore costly to synthesize, elimination of their production in a high-CO₂ environment could provide a significant metabolic benefit to cyanobacteria. Integrating these results with a macroscopic growth model will improve understanding of cyanobacterial growth on an industrial scale.