Staph Favors Heme

MICROBIOLOGY

Life is full of choices, even for bacteria. Staphylococcus aureus, a bacterial species that causes a wide range of "staph" infections, including pneumonia, requires iron to thrive in an animal host. It could obtain iron from heme (the iron-containing porphyrin of hemoglobin) or from transferrin (an iron-transporting protein). Now, researchers at the University of Chicago have found that, during the initial phases of infection, S. aureus displays a strong preference for getting its iron from heme [Science, 305, 1626 (2004)].

The work provides the first evidence that a microorganism can select a specific source of iron from a menu of choices, says Olaf Schneewind, the microbiology professor who led the team.

The researchers also identified a new gene cluster dubbed hts that accounts for S. aureus' fondness for heme iron. The gene cluster codes for heme-uptake proteins that will provide new targets for developing therapeutic agents against staph infections, Schneewind tells C&EN.

The team grew S. aureus in the presence of equal amounts of heme and transferrin-iron. Each of these iron sources was labeled with a different iron isotope. By using inductively coupled plasma-mass spectrometry to measure the isotope content of the bacterial cells, the researchers were able to discern that the bacteria take up most of their iron from heme.

When Schneewind and coworkers infected worms and mice with S. aureus that had mutations in hts genes, they found evidence that the bacteria's pathogenicity was markedly diminished early on, compared to unmutated staph.