With the need to feed our growing human population and increasing evidence for the threat of global warming, a means of channeling greenhouse gasses such as CO2 into food, feed or fuel is a good avenue to simultaneously deal with two of humanity’s major challenges. In nature, carbon fixation by autotrophic organisms is the gateway of inorganic carbon into the living world and is the process which all living organisms depend on for energy and food. Several pathways have evolved to use CO2 as a carbon source but the Calvin-Benson-Bassham (CBB) cycle is by far the most dominant and relies on the carboxylation activity of Ribulose Bisphosphate Carboxylase/Oxygenase (Rubisco), a relatively inefficient enzyme because of both its relatively slow catalytic rate and its inability to distinguish efficiently between O2 and CO2. This issue has been addressed by evolution in many autotrophic organisms that developed a solution in the form of carbon concentrating mechanisms (CCMs), encapsulating Rubisco in an environment rich with CO2 and poor with O2. In agriculture, improvement of the carbon fixation process might increase crop yield and would lead to a more efficient use of resources such as water or land. Additionally, in the biotechnology industry a versatile biological platform able to create compounds of interest from CO2 could be of great significance in halting CO2 atmospheric accumulation. With the ERC support, we were able to introduce a non-native CBB cycle into E. coli, a model heterotrophic organism, gaining the ability to grow on CO2 as a sole carbon source in an environment of 10% partial pressure CO2, rendering the bacteria a synthetic autotroph. Beyond this breakthrough we also characterized essential mutations leading to this phenotype and made progress in shedding light on their molecular mechanism.
