초록
<P><B>ABSTRACT</B></P><P>The chemolithoautotrophic bacterium <I>Acidithiobacillus ferrooxidans</I> 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<SUP>2+</SUP>) and productivities (g IBA/L/d). Medium pH, ferrous concentration (Fe<SUP>2+</SUP>), 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<SUP>3+</SUP> 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<SUP>3+</SUP> to Fe<SUP>2+</SUP> 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. Biotechnol. Bioeng. 2016;113: 790–796. © 2015 Wiley Periodicals, Inc.</P>