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Appl Environ Microbiol, May 1998, p. 1594-1600, Vol. 64, No. 5
Department of Microbiology, Groningen
Biotechnology and Biomolecular Sciences Institute, University of
Groningen, 9751NN Haren, The Netherlands,1 and
Departement de Microbiologie-Biotechnologie,
ENS-BANA, Université de Bourgogne, 21000 Dijon,
France2
Received 11 November 1997/Accepted 9 February 1998
Citrate metabolism in the lactic acid bacterium Leuconostoc
mesenteroides generates an electrochemical proton gradient across the membrane by a secondary mechanism (C. Marty-Teysset, C. Posthuma, J. S. Lolkema, P. Schmitt, C. Divies, and W. N. Konings, J. Bacteriol. 178:2178-2185, 1996). Reports on the energetics of citrate
metabolism in the related organism Lactococcus lactis are
contradictory, and this study was performed to clarify this issue.
Cloning of the membrane potential-generating citrate transporter (CitP)
of Leuconostoc mesenteroides revealed an amino acid
sequence that is almost identical to the known sequence of the CitP of
Lactococcus lactis. The cloned gene was expressed in a
Lactococcus lactis Cit
0099-2240/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Mechanism of the Citrate Transporters in
Carbohydrate and Citrate Cometabolism in Lactococcus and
Leuconostoc Species
strain, and the gene
product was functionally characterized in membrane vesicles. Uptake of
citrate was counteracted by the membrane potential, and the transporter
efficiently catalyzed heterologous citrate-lactate exchange. These
properties are essential for generation of a membrane potential under
physiological conditions and show that the Leuconostoc CitP
retains its properties when it is embedded in the cytoplasmic membrane
of Lactococcus lactis. Furthermore, using the same criteria
and experimental approach, we demonstrated that the endogenous CitP of
Lactococcus lactis has the same properties, showing that
the few differences in the amino acid sequences of the CitPs of members
of the two genera do not result in different catalytic mechanisms. The
results strongly suggest that the energetics of citrate degradation in
Lactococcus lactis and Leuconostoc
mesenteroides are the same; i.e., citrate metabolism in
Lactococcus lactis is a proton motive force-generating
process.
*
Corresponding author. Mailing address: Department of
Microbiology, Biological Centre, Kerklaan 30, 9751NN Haren, The
Netherlands. Phone: 31-50-3632155. Fax: 31-50-3632154. E-mail:
j.s.lolkema{at}biol.rug.nl.
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