Anthrax Spores Use Failsafe Germination System
John Ireland and Philip Hanna
Photo: Bill Wood
Protected by a tough outer coat that is impervious to cold, heat, drought and
harsh chemicals, anthrax spores can remain dormant in the soil for decades.
Once inside a living host, however, they can shed that coat, germinate and begin
infecting cells in as little as 10 minutes.
Scientists know very little about what triggers an anthrax spore to break dormancy.
Identifying the biochemical signals that start the process is an important first
step in preventing anthrax infection.
A study by Medical School scientists John A.W. Ireland, Ph.D., and Philip C.
Hanna, Ph.D., shows that germination requires the coordinated activity of several
genes, receptor proteins and amino acids in at least two simultaneous signaling
pathways. The U-M study, published in the March 2002 issue of the Journal of
Bacteriology, is the first to match anthrax genes with specific amino acids
and signaling pathways that trigger germination.
“Anthrax doesn’t rely on a single signal,” says Hanna, an
assistant professor of microbiology and immunology. “Spores have a redundant
germination mechanism. It’s the bug’s way of ensuring that it won’t
lose its protective armor until conditions are right for germination.”
Hanna and Ireland discovered that amino acids, the fundamental building blocks
of all proteins in the body, in combination with purine ribonucleosides, the
building blocks of DNA and RNA, are triggers for anthrax spore germination.
The process appears to begin when receptor proteins on the spore’s membrane
bind to ring-shaped or aromatic structures found on certain amino acids and
“The receptor protein is the lock and ring structures are the keys,”
says Ireland, a U-M post-doctoral research fellow.
“The only place we know where all the required elements for germination
are present is inside our cells, especially our phagocytes — the scavenger
cells of the immune system,” Ireland explains. “But even in the
macrophage, where conditions are perfect for germination, the spore stays intact
until at least two separate signaling pathways are activated.”
Because it can be handled safely outside a high-level bio-containment laboratory,
Hanna and Ireland used Sterne-based strains of anthrax in their research. The
Sterne strain has been altered, so it cannot infect people.
In future research, Hanna will test the amino acids and ribonucleosides to see
if they trigger anthrax spore germination in tissue cultures. Eventually, he
hopes to expand the study to animal models. His research is supported by the
National Institutes of Health and the Office of Naval Research.
Full text of the published article is available on the American Society of Microbiology
To learn more about Hanna’s research, go to:
To learn more about anthrax, see the U.S. Center for Disease Control Web site: