Terrorism experts have long worried about the use of bacteria or viruses to wipe out whole city centers. With the terrorist attacks on the World Trade Center and the Pentagon, U.S. officials are taking an even keener interest in biological agents. Now, two groups of scientists report progress in taming anthrax - one of the most potent biological agents.

Anthrax is thought to be the biological weapon of choice of bio-terrorists. A person doesn't have to inhale much of the poisonous bacteria to be stricken. A lethal dose of the spores can fit on the head of a pin. Once inside the body, the bacteria begin to rapidly reproduce and release a fatal toxin.

Right now, antibiotics are the only treatment. But there may be another in the making. John Collier is a researcher at Harvard University in Cambridge, Massachusetts. Professor Collier and colleagues are working on a protein inhibitor that would keep anthrax from producing its toxin inside the lungs.

"This would only be used in an attack," he explains. "This inhibitor would be used as early as possible in the course of the disease. And the hope would be that, by blocking toxin action, they would enable the body to overcome the infection by the bacteria. The inhibitors would also block the formation of symptoms from the toxin. So it would be an ancillary treatment to antibiotics. Antibiotics in general cannot rescue a victim of anthrax once symptoms have appeared."

Professor Collier says two versions of the inhibitor were tested on lab animals. They were mixed with anthrax toxin and injected into rats.

"They totally blocked lethality. In fact, we saw no symptoms whatsoever," Professor Collier says.

An article describing the work with anthrax protein inhibitors appears in the October issue of Nature Biotechnology.

In another paper published in the journal Current Biology, researchers identify a gene that makes some mice resistant to anthrax toxin. The investigators from the Howard Hughes Medical Institute in Boston and the Whitehead Institute for Biomedical Research were led by Harvard University assistant professor William Dietrich.

Professor Dietrich says anthrax toxin normally attacks and destroys immune system cells called macrophages. After that, poisoning is swift. However, mice with a variation in a so-called motor gene are immune to the toxin and their microphages remain intact to resist the anthrax assault.

William Dietrich says one possibility now is to test humans for the mutant gene.

"One of the important things that we know is that this gene that exists in mice also exists in humans and in other mammalian species," he says. "Ultimately that might lead to the ability to diagnose or identify individuals who are more or less naturally susceptible to the effects of the toxin. "

Professor Dietrich says researchers are interested in learning more about the motor protein and what it carries around the body, with an eye toward another possible treatment for anthrax poisoning.

The concern about bio-terrorism has resulted in a windfall of money for research. Harvard University's John Collier has been investigating anthrax for 15 years, and he says he's never received so much funding as now.