K-052. Model-Based Analysis of Proton Production and Consumption during Growth of Geobacter Species and Escherichia coli

K. Srinivasan1, M. Izallalen2, D. R. Lovley2, R. Mahadevan1;
1Univ. of Toronto, Toronto, ON, CANADA, 2Univ. of Massachusetts, Amherst, MA.

Production or consumption of protons during microbial metabolism may have important environmental consequences. For example, changes in environmental pH resulting from microbial metabolism may influence the geochemical speciation of many elements in subsurface environments. Furthermore, accumulation of protons within the anode biofilms of microbial fuel cell shave been hypothesized to limit current production. Recently generated genome-scale metabolic models incorporate detailed biochemical information including elemental and charge balanced metabolic reactions, which are generally used to predict rates of substrate uptake and electron acceptor utilization. However, they also have the potential to predict proton secretion and consumption rates. The in silico analysis of Geobacter sulfurreducens metabolism revealed that differences in global intracellular proton balance led to lowered biomass yields during growth with extracellular electron acceptors such as Fe(III), relative to the growth with electron acceptors reduced in the cytosol, such as fumarate. A similar analysis of aerobic growth of E. coli indicated that there could be net production or consumption of protons depending on whether the electron donor was acetate or glucose. In order to test the predictions of the models G. sulfurreducens, G. metallireducens or E. coli were cultured in a 5 L bioreactor with external pH control in the absence of buffer and the amount of acid or based added was measured. The experimentally observed proton production or consumption in cultures of E. coli growing on different carbon sources and Geobacter species growing on acetate with different electron acceptors were consistent with the model predictions. These models that can predict the rate of proton secretion or consumption under a wide range of environmental conditions will be valuable in modeling approaches to the optimization of power production in microbial fuel cells and the in situ bioremediation of contaminated subsurface environments.