Electrofuel Production Using Genetically Engineered Acidithiobacillus Ferrooxidans

We have been developing an electrofuels platform for the production of fuels and chemicals from dilute CO₂ using electricity.  The electricity can come from diverse sources which enables this technology to serve as an alternative means for storing and utilizing renewable energy.   The process uses Acidothiobacillus ferrooxidans which are chemolithoautotrophic bacteria that can oxidize iron at low pH.  The oxidized iron can be reduced electrochemically and recycled to the bioreactor.  We have extensively characterized the growth of the wild type Acidothiobacillus ferrooxidans cells in continuous cultures and we have found that the use of chelators such as citric acid can enable growth at higher pH ranges which can improve growth efficiency, maximum cell yields, and steady state cell densities.  We have also developed a platform for genetically modifying the Acidothiobacillus ferrooxidans cells and we have now expressed 4 different exogenous genes in this host organism.  This is enabling us to explore new promoters and regulatory sequences to direct carbon flux through new synthetic metabolic pathways.  For example, we have introduced a pathway for isobutyric acid production and the results of the characterization of these new cell lines will be presented. 

We have developed an optimized media formulation for combining the biochemical and electrochemical reactors together, and we have performed extended experiments of the integrated system using wild type cells, allowing us to calculate biomass produced per kWhr of electricity under different operating conditions.  We have also build a prototype system with some process control to enable longer term evaluation of the electrofuels platform, and the latest results of this technology will be presented.