永續計畫資料庫

The increasing CO2 concentration in the atmosphere calls for novel approaches for CO2 conversion and utilization with a capacity of GtCO2/year. So far, biology is still the most promising approach to convert CO2 to fuel and chemicals. Here, we propose two integrative systems, one is cell-free, the other involves microorganisms. These systems will utilize renewable electricity as the energy source, electrochemical reactions for cofactor regeneration, biological components as catalysts for the CO2 fixing and conversion, and fiber-optics based device as the control system, to convert CO2 to higher carbon compounds such as alcohols and fatty acids.           

In Subproject 1, we propose the first cell-free, self-replenishing, electro-powered, opto-controlled CO2 fixing machine to achieve CO2 fixation rate at 10 g/L/day for 10 days in the scale of at least 1L. This cell-free system is based on our original model exhibiting an oxygen insensitive, self-replenishing CO2 fixation cycle. This cycle comprises the reductive glyoxylate and pyruvate synthesis (rGPS) cycle and the malyl-CoA-glycerate (MCG) pathway to produce essential intermediates from CO2 in the cycle, acetyl-coenzyme A (acetyl-CoA), pyruvate, and malate. This cycle is equipped with automatically controlled and opto-sensing modules for the regeneration of the cofactors. Its preliminary 12-hour operation with a CO2 fixing rate more than 1 g/L/day has exceeded the native CO2 fixing rate of photosynthetic or lithoautotrophic organisms. In this proposal, we are aiming to further integrate this system with electrochemical means. In return, all required reducing equivalents for CO2 fixation are provided from renewable energy. In addition, both of the electrochemical and biochemical reactions are monitored and controlled by the optical system. The stability of enzyme and metabolites is studied and improved for the enhancement of robustness and suitability of our system.         

 In Subproject 2, we propose two microorganism-based CO2 fixation systems utilizing different electron carriers, formic acid and H2. The main scope of Subproject 2A is the development of an electricity powered, glucose-assisted CO2 fixation system using E. coli NOG or MCG strains. The NOG and MCG pathways have been demonstrated by us to avoid the intrinsic carbon loss in the pyruvate-to-acetyl-CoA step, showing the production of more than 2 moles of acetate from 1 mole of glucose. The results exceed the theoretic carbon yield from glucose via the EMP route. To realize the full potential of NOG and MCG, generation of more reduced biomass products is in need. In this proposal, we are aiming to build a scalable/sustainable/industrially relevant system which can produce ethanol and higher carbon products from glucose and CO2 in more than 100% carbon yield, assisted by electrochemical produced formic acid. The parameters for electrochemical formate production are to be improved to less than 0.3 V overpotential, 100-200 mA/cm2 current density and >95% Faraday efficiency. The NOG and MCG strains are also further engineered through rational design according to evolution processes.          

The main scope of Subproject 2B is to construct bio-inorganic hybrid catalysts for electricity-to-chemical conversions using surface-engineered lithoautotrophic organisms, such as Ralstonia eutropha and Moorella thermoacetica. Herein, we propose a novel approach to anchor inorganic electrocatalysts onto the bacterial membrane for in situ hydrogen generation. By this design, we are able to mitigate the low solubility, low mass transfer rate and the safety concern imposed by the use of molecular H2 gases. It facilitates fast H2 utilization within microorganisms and enhances their carbon conversion yield. Evolution of R. eutropha and M. thermoacetica is also investigated in the electrolytic conditions to alleviate the dependency on anti-oxidants.