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Infection and Immunity, November 2001, p. 6951-6961, Vol. 69, No. 11
0019-9567/01/$04.00+0   DOI: 10.1128/IAI.69.11.6951-6961.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Heme Utilization in Bordetella avium Is Regulated by RhuI, a Heme-Responsive Extracytoplasmic Function Sigma Factor

Amy E. Kirby, Daniel J. Metzger, Erin R. Murphy, and Terry D. Connell*

Witebsky Center for Microbial Pathogenesis and Immunology and Department of Microbiology, School of Medicine and Biomedical Sciences, The University at Buffalo, The State University of New York, Buffalo, New York 14214

Received 7 June 2001/Returned for modification 26 July 2001/Accepted 7 August 2001

Efficient utilization of heme as an iron (Fe) source by Bordetella avium requires bhuR, an Fe-regulated gene which encodes an outer membrane heme receptor. Upstream of bhuR is a 507-bp open reading frame, hereby designated rhuI (for regulator of heme uptake), which codes for a 19-kDa polypeptide. Whereas the 19-kDa polypeptide had homology to a subfamily of alternative sigma factors known as the extracytoplasmic function (ECF) sigma factors, it was hypothesized that rhuI encoded a potential in-trans regulator of the heme receptor gene in trans. Support for the model was strengthened by the identification of nucleotide sequences common to ECF sigma-dependent promoters in the region immediately upstream of bhuR. Experimental evidence for the regulatory activities of rhuI was first revealed by recombinant experiments in which overproduction of rhuI was correlated with a dramatically increased expression of BhuR. A putative rhuI-dependent bhuR promoter was identified in the 199-bp region located proximal to bhuR. When a transcriptional fusion of the 199-bp region and a promoterless lacZ gene was introduced into Escherichia coli, promoter activity was evident, but only when rhuI was coexpressed in the cell. Sigma competition experiments in E. coli demonstrated that rhuI conferred biological properties on the cell that were consistent with RhuI having sigma factor activity. Heme, hemoglobin, and several other heme-containing proteins were shown to be the extracellular inducers of the rhuI-dependent regulatory system. Fur titration assays indicated that expression of rhuI was probably Fur dependent.

* Corresponding author. Mailing address: Department of Microbiology, 138 Farber Hall, 3435 Main St., The University of Buffalo, The State University of New York, Buffalo, NY 14214. Phone: (716) 829-3364. Fax: (716) 829-2158. E-mail: connell{at}acsu.buffalo.edu.

Infection and Immunity, November 2001, p. 6951-6961, Vol. 69, No. 11
0019-9567/01/$04.00+0   DOI: 10.1128/IAI.69.11.6951-6961.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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