Genetic engineering of cyanobacteria for increased CO2-fixation and redirected carbon metabolism

Our research project

Photosynthesis is the key biological process utilizing solar energy to convert water and air (CO2) into chemically fixed carbon. All photosynthetic organisms (plants, algae, and photosynthetic bacteria) harvest solar energy using dedicated pigments with specific chlorophyll molecules use the collected energy to generate high-level electrons by splitting water in the photosystem 2. Energy and electrons, delivered from the light dependent process in the form of ATP and NADPH, respectively, are used to convert CO2 into primary sugars. As the main biological process it provides the globe with e.g. all primary food and biomass.

In addition of being dependent on solar energy, photosynthesis is clearly limited by the availability of CO2. Any increase from the natural 0.04% CO2 in air will increase the rate of CO2 fixation and subsequently generate more primary sugars and thereby biomass and further products. Through evolution different mechanisms to take up and fix CO2 has been developed in photosynthetic organisms with the main enzyme complex being Ribulose 1,5-Bisphosphate Carboxylase Oxygenease (RuBisCO), the primary CO2 fixing enzyme in the Calvin cycle. However, evolution did not develop the most efficient RuBisCO, in addition to fix CO2 (carboxylase activity) it also has the capacity to fix O2 (oxygenase activity).

Native and engineered cyanobacteria have been used by us and many other laboratories as model systems for a long time to examine, demonstrate and develop photobiological H2 production. In addition, more recently also the production of carbon-containing solar fuels like ethanol, butanol and isoprene have been demonstrated. In addition, similar approaches have been used to engineer cyanobacteria to actively produce carbon-containing molecules like sugars, carbohydrates and other organic molecules. In these context the cyanobacterial cell can be seen as a photosynthetic microbial cell factory using solar energy to drive the production of the selected and desired compound. The carbon content of the produced compound has it origin in photosynthetic CO2 fixation, a limiting pathway for increased efficiency and sustainable production. From an environmental perspective the cyanobacterial cell is a sink for CO2 thereby reducing its negative effect on the climate.

In the present project we explore different strategies for increased CO2 fixation and thereby increased productivity. In addition, we address the potential of redirecting the native carbon metabolism for a desired purpose.

Reference

• Liang, Lindblad (2017) Synechocystis PCC 6803 overexpressing RuBisCO grow faster with increased photosynthesis. Metabolic Engineering Communications 4: 29-36. (doi: 10.1016/j.meteno.2017.02.002.)
• Liang, Lindblad (2016) Effects of overexpressing photosynthetic carbon flux control enzymes in the cyanobacterium Synechocystis PCC 6803. Metabolic Engineering 38: 56-64. (doi: 10.1016/j.ymben.2016.06.005.)
• Durall, Rukminasari, Lindblad (2016) Enhanced growth at low light intensity in the cyanobacterium Synechocystis PCC 6803 by overexpressing phosphenolpyruvate carboxylase. Algal Research 16: 275-281. (doi: 10.1016/ j.algal.2016.03.027.)
• Durall, Lindblad (2015) Mechanisms of carbon fixation and engineering for increased carbon fixation in cyanobacteria. Algal Res 11: 263-270. (doi: 10.1016/j.algal.2015.07.002)