(SEMINARIUM) Professor Maurycy Daroch, School of Environment and Energy, Peking University, China

Over the last 2.5 billion years, cyanobacteria equipped with the Calvin cycle transformed the atmosphere and fertilised our entire planet, allowing for the evolution of complex life forms including terrestrial plants, that to this day are the foundation of our agriculture and economy. This makes these photosynthetic bacteria arguably the most important group of microorganisms to have ever existed on Earth.

Despite their evolutionary success, attempts to further improve the canonical carbon fixation pathway i.e. Calvin Benson Bassham cycle, suggest that this mechanism of carbon reduction may have reached its limits and that more radical designs may be required.

In the last three years our team has embarked on the exciting journey to reconstruct the central metabolic pathways of carbon fixation and developed the concept of cyanobacterial photochemotrophy. In this presentation I introduce this approach and present current most promising strategies to reroute carbon delivery and fixation in a model cyanobacterium Synechococcus elongatus through application of alternative C1 molecules as carbon carriers. In the reconstructed strains of this model cyanobacterium, formate is used as a primary carbon source and integrated into the central metabolism through both native carbon fixation cycle and reductive glycine pathway. The energy and reducing equivalents for the carbon fixation, in the form of NADPH and ATP, are provided by native photosystems. The isotopologue analysis revealed that the leading reconstructed strains exhibit high levels of 13C formate incorporation across major central metabolites such as G3P. DHAP, G1P, FBP, when compared with the wild-type strain grown in 13 C formate medium, and near-complete label incorporation in several key amino acids.

The proposed approach will hopefully lead, in a near term, to a wider interest in rewiring central metabolic pathways of primary producers with synthetic C1 assimilation modules. Meanwhile the ultimate goal of this research is to generate a new type of metabolism to entirely replace the inefficient Calvin cycle and allow the new iteration of refactored cyanobacteria to once again take the central stage in carbon fixation on Earth and play a pivotal role in reversing anthropogenic climate change and becoming new platforms for bioproduction of commodities from C1 intermediates.