Kinetic and stoichiometric characterization of organoautotrophic growth of Ralstonia eutropha on formic acid in fed‐batch and continuous cultures. Issue 1 (13th August 2014) - Grunwald, Stephan
Summary Formic acid, acting as both carbon and energy source, is a safe alternative to a carbon dioxide, hydrogen and dioxygen mix for studying the conversion of carbon through the Calvin–Benson–Bassham (CBB) cycle into value‐added chemical compounds by non‐photosynthetic microorganisms. In this work, organoautotrophic growth of Ralstonia eutropha on formic acid was studied using an approach combining stoichiometric modeling and controlled cultures in bioreactors. A strain deleted of its polyhydroxyalkanoate production pathway was used in order to carry out a physiological characterization. The maximal growth yield was determined at 0.16 Cmole Cmole−1 in a formate‐limited continuous culture. The measured yield corresponded to 76% to 85% of the theoretical yield (later confirmed in pH‐controlled fed‐batch cultures). The stoichiometric study highlighted the imbalance between carbon and energy provided by formic acid and explained the low growth yields measured. Fed‐batch cultures were also used to determine the maximum specific growth rate (μmax = 0.18 h−1) and to study the impact of increasing formic acid concentrations on growth yields. High formic acid sensitivity was found in R eutropha since a linear decrease in the biomass yield with increasing residual formic acid concentrations was observed between 0 and 1.5 g l−1.