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Citrate utilization by Escherichia coli: plasmid- and chromosome-encoded systems
Journal of Bacteriology
|December 1, 1983
Summary
Citrate utilization in Escherichia coli involves inducible transport systems, whether plasmid- or chromosome-mediated. Both systems show energy-dependent transport in membrane vesicles, with proton gradients being crucial for citrate uptake.
Area of Science:
- Microbiology
- Molecular Biology
- Biochemistry
Background:
- Citrate utilization (Cit+) variants of Escherichia coli have been observed in atypical isolates and through chromosomal mutations.
- Understanding the mechanisms of citrate transport is essential for characterizing E. coli metabolic capabilities.
Purpose of the Study:
- To investigate and compare the citrate transport processes in a chromosomal Cit+ mutant and a plasmid-mediated Cit+ system in E. coli.
- To elucidate the role of induction, energy dependence, and specific ions in citrate uptake.
Main Methods:
- Growth experiments to assess induction of citrate utilization.
- Whole-cell transport assays using radiolabeled citrate ([1,5-14C]citrate and [6-14C]citrate).
- Membrane vesicle transport assays to study energy-dependent transport and kinetics.
Main Results:
- Both chromosomal and plasmid Cit+ systems are inducible, with induced cells showing higher citrate accumulation rates.
- Energy-dependent citrate transport was observed in membrane vesicles, sensitive to protonophores but not ionophores.
- Proton (H+) gradients were important for transport, while monovalent/divalent cations and certain anions were not required.
Conclusions:
- Citrate transport in E. coli is an inducible, energy-dependent process.
- Proton motive force plays a key role in facilitating citrate uptake.
- Differences exist between chromosomal and plasmid-mediated citrate transport systems, particularly in their response to citrate analogs.