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Staphylococcus aureus Growth using Human Hemoglobin as an Iron Source
Published on: February 7, 2013
Identification of a hemin utilization protein of Moraxella catarrhalis (HumA)
Kristin Furano1, Anthony A Campagnari
1Department of Microbiology and Immunology, State University of New York at Buffalo, 14214, USA.
Abstract:
Moraxella catarrhalis is a major cause of acute otitis media in young children and has also been implicated as an important cause of exacerbations in adults with underlying pulmonary disease. Due to the considerable level of antibiotic resistance and the high degree of carriage rates in young children, it is likely that the incidence of M. catarrhalis infections will continue to rise. M. catarrhalis is a strict human respiratory pathogen, and this bacterium uses both transferrin and lactoferrin receptors to fulfill the essential iron requirement for survival in vivo. However, these are the only described iron acquisition systems for this organism. In this report we have demonstrated that M. catarrhalis can also utilize hemin as a sole source of iron for growth. In addition, we have identified and characterized an outer membrane protein with homology (26 to 28% similarity) to other known hemin binding and uptake proteins in related gram-negative organisms (i.e., Bordetella and Yersinia spp.). This newly described M. catarrhalis protein, termed HumA, is capable of directly binding to hemin coupled to a solid-phase matrix. M. catarrhalis HumA expressed on the surface of an Escherichia coli hemA-deficient strain (K-12 EB53) is fully capable of complementing the defect and thus restoring the ability of this strain to grow in the presence of hemin. When M. catarrhalis is grown in the presence of hemin, HumA expression is clearly increased as shown by Western blotting with polyclonal antiserum developed against a HumA peptide. In addition, growth analyses revealed that a HumA-deficient mutant of M. catarrhalis (7169::humA) is restricted for growth in the presence of hemin as the sole iron source compared to the wild-type strain. We conclude that HumA is an essential component of a hemin uptake and utilization system previously undescribed for M. catarrhalis, thus providing another mechanism of iron acquisition that may facilitate persistent colonization of the mucosal surface.
Insights
Moraxella catarrhalis, a pathogen causing ear infections and lung disease exacerbations, can now be shown to acquire iron using a novel hemin uptake system. This discovery reveals a new mechanism for bacterial survival and colonization.
Area of Science:
- Microbiology
- Bacterial Pathogenesis
- Iron Metabolism
Background:
- Moraxella catarrhalis is a significant human respiratory pathogen.
- It causes acute otitis media in children and exacerbations in adults with pulmonary disease.
- Known iron acquisition systems include transferrin and lactoferrin receptors.
Purpose of the Study:
- To investigate alternative iron acquisition mechanisms in M. catarrhalis.
- To identify and characterize novel proteins involved in iron uptake.
- To understand how M. catarrhalis obtains iron for survival and colonization.
Main Methods:
- Demonstration of hemin utilization for growth.
- Identification and characterization of a novel outer membrane protein, HumA.
- Functional complementation of an E. coli hemA-deficient strain with M. catarrhalis HumA.
- Analysis of HumA expression and growth of a HumA-deficient mutant.
Main Results:
- M. catarrhalis can utilize hemin as a sole iron source.
- A novel outer membrane protein, HumA, with homology to hemin uptake proteins was identified.
- HumA directly binds hemin and its expression is upregulated in the presence of hemin.
- A HumA-deficient mutant showed restricted growth with hemin as the sole iron source.
Conclusions:
- HumA is essential for a previously undescribed hemin uptake and utilization system in M. catarrhalis.
- This system provides an additional mechanism for iron acquisition.
- This mechanism may contribute to persistent colonization of mucosal surfaces by M. catarrhalis.
