DctA- and Dcu-independent transport of succinate in Escherichia coli: contribution of diffusion and of alternative carriers

Citation
Ig. Janausch et al., DctA- and Dcu-independent transport of succinate in Escherichia coli: contribution of diffusion and of alternative carriers, ARCH MICROB, 176(3), 2001, pp. 224-230
Citations number
23
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Microbiology
Journal title
ARCHIVES OF MICROBIOLOGY
ISSN journal
0302-8933 → ACNP
Volume
176
Issue
3
Year of publication
2001
Pages
224 - 230
Database
ISI
SICI code
0302-8933(200109)176:3<224:DADTOS>2.0.ZU;2-1
Abstract
Quintuple mutants of Escherichia coli deficient in the C-4-dicarboxylate ca rriers of aerobic and anaerobic metabolism (DctA, DcuA, DcuB, DcuC, and the DcuC homolog DcuD, or the citrate/succinate antiporter CitT) showed only p oor growth on succinate (or other C-4-dicarboxylates) under oxic conditions . At acidic pH (pH 6) the mutants regained aerobic growth on succinate, but not on fumarate. Succinate uptake by the mutants could not be saturated at physiological succinate concentrations (less than or equal to5 mM), in con trast to the wild-type, which had a K-m for succinate of 50 (M mu) and a V- max of 35 U/g dry weight at pH 6. At high substrate concentrations, the mut ants showed transport activities (32 U/g dry weight) comparable to that of the wild-type. In the wild-type using DctA as the carrier, succinate uptake had a pH optimum of 6, whereas succinate uptake in the mutants was maximal at pH 5. In the mutants succinate uptake was inhibited competitively by mo nocarboxylic acids. Diffusion of succinate or fumarate across phospholipid membranes (liposomes) was orders of magnitude slower than the transport in the wild-type or the mutants. The data suggest that mutants deficient in Dc tA, DcuA, DcuB, DcuC, DcuD (or CitT) contain a carrier, possibly a monocarb oxylate carrier, which is able to transport succinate, but not fumarate, at acidic pH, when succinate is present as a monoanion. Succinate uptake by t his carrier was inhibited by addition of an uncoupler. Growth by fumarate r espiration (requiring fumarate/succinate antiport) was also lost in the qui ntuple mutants, and growth was not restored at pH 6. In contrast, the efflu x of succinate produced during glucose fermentation was not affected in the mutants, demonstrating that, for succinate efflux, a carrier different fro m, or in addition to, the known Dcu and CitT carriers is used.