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The Iron-Regulated iupABC Operon Is Required for Saprophytic Growth of the Intracellular Pathogen Rhodococcus equi at Low Iron Concentrations

Raúl Miranda-CasoLuengo,¹ Pamela S. Duffy,¹ Enda P. O'Connell,¹ Brian J. Graham,¹ Michael W. Mangan,^1, John F. Prescott,² and Wim G. Meijer^1*

Department of Industrial Microbiology, Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Dublin 4, Ireland,¹ Department of Pathobiology, University of Guelph, Guelph, Ontario N1G 2W1, Canada²

Received 14 December 2004/ Accepted 9 February 2005

Rhodococcus equi is a facultative intracellular pathogen which proliferates rapidly in both manure-enriched soil and alveolar macrophages. Although both environments are characterized by extremely low concentrations of free iron, very little is known regarding the strategies employed by R. equi to thrive under these conditions. This paper reports the characterization of an R. equi transposome mutant that fails to grow at low iron concentrations. The transposome was shown to be inserted into iupA, the first gene of the iupABC operon encoding an ABC transport system highly similar to siderophore uptake systems. Disruption of the iupA gene also resulted in a failure of R. equi to utilize heme and hemoglobin as a source of iron. Introduction of the iupABC operon in trans restored the wild-type phenotype of the mutant strain. iupABC transcripts were 180-fold more abundant in R. equi grown in iron-depleted medium than in organisms grown in iron-replete medium. Proliferation of the iupABC mutant strain in macrophages was comparable to that of the wild-type strain. Furthermore, the iupABC mutant was not attenuated in mice, showing that the iupABC operon is not required for virulence.

Present address: Department of Microbiology, Moyne Institute of Preventive Medicine, University of Dublin, Dublin 2, Ireland.

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