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Intracellular cyclic AMP concentration is decreased in Salmonella typhimurium fur mutants

Department of Genetics and Microbiology, Universitat Autònoma de Barcelona¹ and Centre de Recerca en Sanitat Animal (CReSA), Universitat Autònoma de Barcelona Institut de Recerca i Tecnologia Agroalimentària (UAB-IRTA)², Bellaterra, 08193 Barcelona, Spain

Author for correspondence: Jordi Barbé. Tel: +34 93 581 1837. Fax: +34 93 581 2387. e-mail: jordi.barbe{at}uab.es

It is known that the Fur protein negatively regulates iron-uptake systems in different bacterial species, including Salmonella typhimurium. In this study it has been shown that the intracellular concentration of cyclic AMP (cAMP) is lower in a knockout S. typhimurium fur mutant than in the wild-type strain. According to this, the expression of two cAMP-regulated genes, such as pepE (encoding an -aspartyl dipeptidase) and the Escherichia coli lac operon, is decreased in S. typhimurium fur cells in comparison with wild-type cells. Introduction of an additional mutation in cpdA, encoding a cyclic 3',5'-cAMP phosphodiesterase, recovers wild-type intracellular cAMP concentration in the S. typhimurium fur mutant. Likewise, expression of pepE and the E. coli lac operon was the same in the S. typhimurium fur cpdA double mutant and the wild-type strain. Moreover, these results also demonstrate that the S. typhimurium Fur protein positively regulates the expression of the flhD master operon governing the flagellar regulon. This positive control must be mediated by binding of the S. typhimurium Fur protein to the flhD promoter as indicated by the fact that this promoter tests positive in a Fur titration assay.

Keywords: gene regulation, iron-uptake system, cpdA

Abbreviations: DPD, 2,2-dipyridyl; FURTA, Fur titration assay

The GenBank accession number for the sequence reported in this paper is AF268282.

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