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Journal of Bacteriology, January 2000, p. 439-447, Vol. 182, No. 2
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Use of Heme Compounds as Iron Sources by Pathogenic Neisseriae Requires the Product of the hemO Gene

Wenming Zhu, Desiree J. Hunt, Anthony R. Richardson, and Igor Stojiljkovic*

Department of Microbiology and Immunology, Emory School of Medicine, Atlanta, Georgia 30322

Received 8 September 1999/Accepted 26 October 1999

Heme compounds are an important source of iron for neisseriae. We have identified a neisserial gene, hemO, that is essential for heme, hemoglobin (Hb), and haptoglobin-Hb utilization. The hemO gene is located 178 bp upstream of the hmbR Hb receptor gene in Neisseria meningitidis isolates. The product of the hemO gene is homologous to enzymes that degrade heme; 21% of its amino acid residues are identical, and 44% are similar, to those of the human heme oxygenase-1. DNA sequences homologous to hemO were ubiquitous in commensal and pathogenic neisseriae. HemO genetic knockout strains of Neisseria gonorrhoeae and N. meningitidis were unable to use any heme source, while the assimilation of transferrin-iron and iron-citrate complexes was unaffected. A phenotypic characterization of a conditional hemO mutant, constructed by inserting an isopropyl-beta -D-thiogalactopyranoside (IPTG)-regulated promoter upstream of the ribosomal binding site of hemO, confirmed the indispensability of the HemO protein in heme utilization. The expression of HemO also protected N. meningitidis cells against heme toxicity. hemO mutants were still able to transport heme into the cell, since both heme and Hb could complement an N. meningitidis hemA hemO double mutant for growth. The expression of the HmbR receptor was reduced significantly by the inactivation of the hemO gene, suggesting that hemO and hmbR are transcriptionally linked. The expression of the unlinked Hb receptor, HpuAB, was not altered. Comparison of the polypeptide patterns of the wild type and the hemO mutant led to detection of six protein spots with an altered expression pattern, suggesting a more general role of HemO in the regulation of gene expression in Neisseriae.

* Corresponding author. Mailing address: Department of Microbiology and Immunology, Emory School of Medicine, 1510 Clifton Rd., Atlanta, GA 30322. Phone: (404) 727-1322. Fax: (404) 727-8250. E-mail: stojiljk{at}microbio.emory.edu.

Journal of Bacteriology, January 2000, p. 439-447, Vol. 182, No. 2
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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