A tricarboxylic acid cycle intermediate regulating transcription of a chloroaromatic biodegradative pathway: Fumarate-mediated repression of the clcABD operon

Sally M. McFall, Binu Abraham, Cristina G. Narsolis, A. M. Chakrabarty*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

63 Scopus citations

Abstract

The ortho-cleavage pathways of catechol and 3-chlorocatechol are central catabolic pathways of Pseudomonas putida that convert aromatic and chloroaromatic compounds to tricarboxylic acid (TCA) cycle intermediates. They are encoded by the evolutionarily related catBCA and clcABD operons, respectively. Expression of the cat and clc operons requires the LysR-type transcriptional activators CatR and ClcR, respectively, and the inducer molecules cis, cis-muconate and 2-chloro-cis, cis-muconate, respectively. The regulation of the cat and clc promoters has been well studied, but the extent to which these operons are repressed by growth in TCA cycle intermediates has not been explored. We demonstrate by transcriptional fusion studies that the expression from the clc promoter is repressed when the cells are grown on succinate, citrate, or fumarate and that this repression is ClcR dependent and occurs at the transcriptional level. The presence of these organic acids did not affect the expression from the cat promoter. In vitro transcription assays demonstrate that the TCA cycle intermediate fumarate directly and specifically inhibits the formation of the clcA transcript. No such inhibition was observed when CatR was used as the activator on either the cat or clc template. Titration studies of fumarate and 2-chloromuconate show that the fumarate effect is concentration dependent and reversible, indicating that fumarate and 2-chloromuconate most probably compete for the same binding site on ClcR. This is an interesting example of the transcriptional regulation of a biodegradative pathway by the intracellular sensing of the state of the TCA cycle.

Original languageEnglish (US)
Pages (from-to)6729-6735
Number of pages7
JournalJournal of bacteriology
Volume179
Issue number21
DOIs
StatePublished - Nov 1997

ASJC Scopus subject areas

  • Microbiology
  • Molecular Biology

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