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Applied and Environmental Microbiology, July 2000, p. 2934-2942, Vol. 66, No. 7
Max-Planck-Institut für terrestrische
Mikrobiologie, D-35043 Marburg, Germany
Received 9 February 2000/Accepted 8 May 2000
Propionate consumption was studied in syntrophic batch and
chemostat cocultures of Syntrophobacter fumaroxidans and
Methanospirillum hungatei. The Gibbs free energy available
for the H2-consuming methanogens was <
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Energetics of Syntrophic Propionate Oxidation in
Defined Batch and Chemostat Cocultures
and
20 kJ mol of
CH4
1 and thus allowed the synthesis of 1/3
mol of ATP per reaction. The Gibbs free energy available for the
propionate oxidizer, on the other hand, was usually >
10 kJ mol of
propionate
1. Nevertheless, the syntrophic coculture grew
in the chemostat at steady-state rates of 0.04 to 0.07 day
1 and produced maximum biomass yields of 2.6 g
mol of propionate
1 and 7.6 g mol of
CH4
1 for S. fumaroxidans and
M. hungatei, respectively. The energy efficiency for
syntrophic growth of S. fumaroxidans, i.e., the biomass
produced per unit of available Gibbs free energy was comparable to a
theoretical growth yield of 5 to 12 g mol of ATP
1.
However, a lower growth efficiency was observed when sulfate served as
an additional electron acceptor, suggesting inefficient energy
conservation in the presence of sulfate. The maintenance Gibbs free
energy determined from the maintenance coefficient of syntrophically
grown S. fumaroxidans was surprisingly low (0.14 kJ
h
1 mol of biomass C
1) compared to the
theoretical value. On the other hand, the Gibbs free-energy dissipation
per mole of biomass C produced was much higher than expected. We
conclude that the small Gibbs free energy available in many
methanogenic environments is sufficient for syntrophic propionate
oxidizers to survive on a Gibbs free energy that is much lower than
that theoretically predicted.
*
Corresponding author. Mailing address:
Max-Planck-Institut für terrestrische Mikrobiologie,
Karl-von-Frisch-Str., D-35043 Marburg, Germany. Phone: 49 (6421) 178 801. Fax: 49 (6421) 178 809. E-mail:
conrad{at}mailer.uni-marburg.de.
Present address: Department of Biological Sciences, University of
Warwick, Coventry CV4 7AL, United Kingdom.
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