UNIFIED MODEL DESCRIBING THE ROLE OF HYDROGEN IN THE GROWTH OF DESULFOVIBRIO-VULGARIS UNDER DIFFERENT ENVIRONMENTAL-CONDITIONS

A unified model for the growth of Desulfovibrio vulgaris under differe nt environmental conditions is presented. The model assumes the existe nce of two electron transport mechanisms functioning simultaneously. O ne mechanism results in the evolution and consumption of hydrogen, as in the hydrogen-cycling model. The second mechanism assumes a direct t ransport of electrons from the donor to the acceptor, without the part icipation of H-2. A combination of kinetic and thermodynamic condition s control the flow of electrons through each pathway. The model was ca librated using batch experiments with D. vulgaris grown on lactate, in the presence and absence of sulfate, and was verified using additiona l batch experiments under different conditions, The model captured the general trends of consumption of substrates and accumulation of produ cts, including the transient accumulation and consumption of H-2. Furt hermore, the model estimated that 48% of the electrons transported fro m lactate to sulfate involved H-2 production, indicating that hydrogen cycling is a fundamental process in D. vulgaris. The presence of simu ltaneous electron transport mechanisms might provide D. vulgaris with important ecological advantages, because it facilitates a rapid respon se to changes in environmental conditions, This model increases our ab ility to study the microbial ecology of anaerobic environments and the role of Desulfovibrio species in a variety of environments. (C) 1998 John Wiley & Sons, Inc.