Expanding the metabolism of the most primitive phototroph

Carbon fixation and conversion into carbohydrate is one of the dominant biochemical processes in nature, supplying the cellular building blocks for all living organisms. The majority of this fixation, or global primary productivity, is performed by plants on land and by algae and cyanobacteria in marine environments using the Calvin cycle, coupled to the conversion of sunlight into chemical energy. This process has produced the environmental conditions that permitted the evolution of complex life on Earth. However, the rate of release of fossil fuel emission is disrupting the delicate gas balance of the atmosphere, leading to global warming and climate breakdown. Beyond cutting greenhouse gas emissions, it is essential that new technologies are developed to capture CO2 from the environment and store it as organic compounds, for which efficient biological routes must be explored.
Alternative carbon fixation pathways are found in microbes dispersed throughout the tree of life. The most ancient of these, the Wood-Ljungdahl pathway, is still used by anaerobic bacteria and archaea found inhabiting environments lacking oxygen. This pathway is the simplest and most energy-efficient route for CO2 capture. Interestingly, the most primitive phototrophs, the anaerobic Heliobacteria, are unable to fix carbon, but they are closely-related to bacteria that use the Wood-Ljungdahl pathway as a source of carbon. This synthetic biology project aims to couple energy-efficient CO2 fixation to phototrophic generation of ATP in Heliobacteria, providing an exciting prospect for carbon capture and storage. The principles defined will be directly applicable to the sustainable generation of renewable chemicals.