What Is Anthrax?
An ancient disease, anthrax is an umbrella term for the dozens of strains of the bacterium Bacillus anthracis. Devastating to livestock, anthrax cells kill host organisms by releasing two kinds of toxins. As the cells multiply in the system, the concentration of toxins increase to lethal levels.
The danger of anthrax (and the reason why the military and terrorists seek it as a biological weapon) is that it forms endospores - a tough structure that protects the cell while it enters a dormant, hibernation state. Endospores allow anthrax to survive in soil, fur, clothing or other inhospitable environments for several years. When the endospore enters a host, it "reactivates" and starts reproducing rapidly.
Anthrax can infect hosts by landing on the skin or ingestion. However, the deadliest form of infection occurs when the spores are inhaled.
The actual process for fabricating weapon-grade anthrax is classified (and for good reason). That said, the military scientists who create this biological weapon of mass destruction most likely use the same protocol medical scientists use to cultivate virulent anthrax spores for the purpose of testing the efficacy of anthrax vaccines. The difference, however, is that the military scientists induce endospore formation, dry the spores and combine them with chemical "stabilizers" that help the spores remain airborne longer.
Mass-Producing the Bacteria
Certain military biodefense laboratories (Fort Detrick, for example) store freeze-dried spores of especially virulent anthrax strains, such as Ames and Vollum. To mass produce these spores, the freeze-dried spores are activated and cultured.
First, the freeze-dried spores are dissolved into 1 ml of saline solution, spread onto a nutrient agar petri dish and allowed to incubate at 37 degrees Celsius for 24 hours. The colonies that form are then transferred to their own nutrient agar petri dishes and allowed to incubate further.
Once enough colonies have formed, the scientists must recreate the "environmental stresses" that cause the anthrax cells to grow the protective endospores. Because anthrax is an aerobic organism, the spore process begins by reducing the amount of oxygen in the environment. The petri dishes are placed in a sealed chamber and carbon dioxide is pumped in until the gas constitutes 50 percent of the total air pressure. Meanwhile, the temperature inside the chamber is lowered to 20 degrees Celsius.
After between 24 and 48 hours, the colonies from the petri dishes are transferred to saline solutions with pH levels balanced to mimic that of a mammalian host. These solutions are loaded into a centrifuge, which helps separate the spores from less-dense contaminants. As each layer of contaminants is removed, more deionized water is added to the spores for subsequent rounds of centrifugal separation.
Once purified, special chemicals (largely classified) are added to the spore-water mixture. From what can be pieced together from news reports, silica seems to be one such chemical, although there might be others. This enriched mixture is turned into powder using a machine known as a spray dryer. In spray drying, a liquid is separated into thousands of microscopic droplets by passing through a high-precision atomizer. These droplets are sprayed directly into a heated chamber; the combination of heat, low humidity and large surface-area-to-volume ratio of the droplets causes the water to evaporate instantly. As a result, the silica and other special chemicals form a partial shell around the individual spores.
This shell helps prevent the spores from clumping together due to humidity. Less clumping means smaller particle sizes, which means that the weaponized spores will remain in the air longer and even bypass certain filter grades.