title: Enhancing isobutyric acid production from engineered Acidithiobacillus ferrooxidans cells via media optimization.
abstract: The chemolithoautotrophic bacterium Acidithiobacillus ferrooxidans has previously been genetically modified to produce isobutyric acid (IBA) from carbon dioxide while obtaining energy from the oxidation of ferrous iron. Here, a combinatorial approach was used to explore the influence of medium composition in both batch and chemostat cultures in order to improve IBA yields (g IBA/mol Fe(2+)) and productivities (g IBA/L/d). Medium pH, ferrous concentration (Fe(2+)), and inclusion of iron chelators all had positive impact on the IBA yield. In batch experiments, gluconate was found to be a superior iron chelator because its use resulted in smaller excursions in pH. In batch cultures, IBA yields decreased linearly with increases in the final effective Fe(3+) concentrations. Chemostat cultures followed similar trends as observed in batch cultures. Specific cellular productivities were found to be a function of the steady state ORP (Oxidation-reduction potential) of the growth medium, which is primarily determined by the Fe(3+) to Fe(2+) ratio. By operating at low ORP, chemostat cultures were able to achieve volumetric productivities as high as 3.8 ± 0.2 mg IBA/L/d which is a 14-fold increase over the previously reported value.
authors.affiliation: Department of Chemical Engineering, Columbia University, New York, New York, 10027.
authors.forename: Xiaozheng
authors.initials: X
authors.lastname: Li
authors.affiliation: Department of Chemical Engineering, Columbia University, New York, New York, 10027.
authors.forename: Alan C
authors.initials: AC
authors.lastname: West
authors.affiliation: Department of Chemical Engineering, Columbia University, New York, New York, 10027. sbanta@columbia.edu.
authors.forename: Scott
authors.initials: S
authors.lastname: Banta
mesh_terms: D042763:Acidithiobacillus / Q000235:genetics* / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism; D002614:Chelating Agents / Q000378:metabolism; D003470:Culture Media / Q000737:chemistry*; D005296:Ferrous Compounds / Q000378:metabolism; D005942:Gluconates / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D058610:Isobutyrates / Q000378:metabolism*; D060847:Metabolic Engineering; D030781:Organisms, Genetically Modified; D010084:Oxidation-Reduction
chemical_list: D002614:Chelating Agents; D003470:Culture Media; D005296:Ferrous Compounds; D005942:Gluconates; D058610:Isobutyrates; D002245:Carbon Dioxide; C020380:isobutyric acid; C030691:gluconic acid
keywords: chemolithoautotroph; electrofuels; iron-oxidizing bacteria; medium formulation