SUPER SPORES
Bacterial spores have survived boiling water, frigid liquid nitrogen, and brief exposure to bleach and other sterilizing chemicals.
They also have withstood the test of time: Spores reportedly have managed for millennia inside Egyptian tombs and the intestines of frozen woolly mammoths - even within a salt crystal that formed 250 million years ago.
And space: Some spore-forming bacteria appear to have held out on the moon for several years, having been left by earlier Apollo missions and recovered by later ones.
No wonder anthrax scares people.
While molds, yeasts, and some other microorganisms form spores, the single-cell genus Bacillus, of which anthrax is a member, is "more macho than other kinds of spores in nature," Harvard microbiologist Richard Losick said. "They are the champions."
Lowly bacteria have achieved what humans can only dream of - the ability to survive for centuries, to come through the most hostile environments, perhaps even travel between planets.
The spore-formation process is among the various survival strategies that bacteria have evolved over nearly four billion years - a history that stretches back far beyond that of plants and animals.
Bacteria are still the dominant life-form on Earth. Every teaspoon of ordinary soil carries thousands of spores, the bulk of them harmless.
Bacillus anthracis and its relatives can exist in either of two states - the active "vegetative" form and the dormant "spore" form - and can switch back and forth as conditions change.
Only in the vegetative state are spore-forming organisms technically alive - capable of reproducing, taking in nutrients, and getting rid of wastes. If they sense a lack of nutrients or water, they take on the much tougher guise of a spore.
"A spore is true suspended animation," Russell Vreeland, a biologist at West Chester University, said.
The only purpose of the spore is to preserve itself.
The outside is a thick, hard shell that provides protection from otherwise fatal heat, cold or chemical assaults.
The inside is almost crystalline in its ordered formation of molecules. The structure is designed entirely to protect the most critical component of the cell, the DNA, which encodes the organism's individual genetic identity.
Faced with an adverse environment that limits nutrients and water, the active bacterium dries out and encases its DNA in an arrangement of proteins that act as molecular-scale packing materials.
Genes embedded in the DNA hold the recipes for making the protective proteins. Some surround the DNA directly while others form the outer shell. Together they shield the DNA from levels of heat, cold or radiation that would kill an ordinary cell.
The drier the conditions, the longer spores can last.
Other genes inside the spore eventually will help it come out of suspended animation. They are triggered when the spore senses sufficient water and nutrients.
In the case of anthrax, the spore bumps into those nutrients in the body of an animal or human, only then turning into its active vegetative form, multiplying and spewing toxins. Experts say anthrax is the only disease caused by spores that are activated in the lungs.
Theoretically, biologist Vreeland said, spores can survive millions - perhaps even billions - of years. Last year, he and colleague William Rosenzweig published a paper in the journal Nature in which they described extracting Bacillus spores from a salt crystal they believed was formed before the age of dinosaurs, then adding nutrients and water to coax them into the vegetative state, grow, and reproduce 250 million years later.
Some of their peers remain unconvinced of the feat, arguing that it's too hard to guarantee the samples weren't contaminated with the similar, modern Bacillus marismorti. Vreeland stands by his work.
In 1995, scientists from California State University, San Luis Obispo, claimed to have cultured bacteria from spores that had spent 25 million years inside the gut of a bee encased in amber. (Two years earlier, it was mosquitoes encased in amber that protected the dinosaur DNA used to grow the creatures in the film Jurassic Park, with one key difference: Since dinosaur cells, like human cells, don't form spores, their ancient DNA was unprotected inside the amber.)
Some scientists question the Cal State claims, too, suspecting that the researchers are seeing ordinary contamination. In theory, however, there's no reason a spore in a protected environment couldn't live for a long, long time.
In fact, scientists exploring the notion of life on other planets have postulated that spore-forming bacteria may have traveled around the solar system embedded in meteorites, for example, that were dislodged from Mars and crashed to Earth. Their statistical models suggest some spores could survive the trip through outer space.
Spores can be killed. But they must be immersed in boiling water much longer than vegetative bacteria or bombarded with far more intense radiation. Many scientists say that irradiating mail with powerful particle or gamma ray beams would kill enough spores to make credit-card bills significantly safer.
Tests show that irradiating mail could destroy 95 percent of anthrax spores, said Calvin Chue, a biochemist at the Johns Hopkins University Center for Civilian Biodefense Studies. High heat - 160 degrees Fahrenheit for 30 minutes or more - also can kill them.
There's no way to make sure mail would be absolutely sterile, Chue said, but it could be made much safer - indeed, anything else living on the envelope certainly would be killed, too.
Flam, Faye. "Super Spores." The Philadelphia Inquirer 5 Nov. 2001. Print.
Anthrax Anxiety: A Reality Check
Here is a comparison of deaths from anthrax for the four weeks ended Friday (Nov 2001) vs. deaths from selected other causes for an average* four-week period.
Cause of death / NumberSmoking-related. / 30,769
Flu-related / 4,899
Auto accidents / 3,264
Alcohol-induced. / 1,468
Murders / 1,295
AIDS / 1,129
Prescription. drug errors. / 538
Firearm accidents / 64
Airline crashes / 7
Lightning strikes / 6
Anthrax / 4
West Nile virus / 0.15
Shark attacks. / 0.08
*Calculated from the most recent annual statistics available for the United States, not adjusted for seasonal fluctuations.
SOURCES: American Cancer Society (smoking, 2000 estimate); Institute of Medicine (prescription drug errors, annual average estimate); National Transportation Safety Board (plane crashes, 2000 actual); National Oceanic and Atmospheric Administration (lightning, annual average); Centers for Disease Control and Prevention (anthrax, Oct. 5 to Nov. 2, 2001; West Nile virus, 2000 actual); International Shark Attack File (sharks, 2000 actual). All other numbers are from the National Center for Health Statistics (1999, actual).
Anthrax Spore – The dark inner area is the DNA and cytoplasm. The outer rings are the coat and exosporium.
www.med.umich.edu/opm/newspage/ images/anthraxspore.jp