Anthrax may be the baddest bacteria on the block, but anthrax gets sick, too. Just like you, bacteria get the bug, viruses called bacteriophages. Bacteriophages are just small viruses, tiny and elegant packages of genes that inject themselves into the machinery of cells, using them to churn out more viruses.
"Every time we open up anthrax, there are viruses inside," says microbiologist Vincent Fischetti of Rockefeller University in New York. "What everyone else thought," Fischetti says, was that these viruses preyed on bacteria, like colds prey on people, making them weaker.
But in 2006, Fischer and his student Raymond Schuch found that anthrax actually weathers the assault of a natural antibiotic better when it's infected with a virus. "That led us to wonder how this deadly bacteria exists when it is outside humans," Fischetti said.
Anthrax is found naturally in the soil, packed into spores in dirt, waiting to be eaten, by grazing livestock. Once inside a creature it spreads, releasing toxins that often kill their host, and deposit more spores in the soil, dormant, waiting for the next victim.
Or so we thought. "Actually the story turns out to be a lot more complicated," Schuch says.
A great deal of research has focused on anthrax after it was used in 2001 to kill five people in mailings linked by the Justice Department to a United States Army Medical Research Institute for Infectious Diseases vaccine researcher, Bruce Ivins, who committed suicide last year. But most of the research focuses on anthrax infections, not on how it spends most of its time in the wild.
In a paper out in the journal PloS One, Fischetti and Schuch looked at how infection with nine bacteriophages affected anthrax, compared to uninfected anthrax, in the soil. "Infection drives a series of changes," they write after a series of experiments:
• They grow in "flat, large, and opaque" colonies, unlike "small, white" uninfected ones.
• Infected spores have double-thick walls that stay within colonies instead of sprouting rapidly.
• Infected spores "colonize" the guts of earthworms much more successfully.
"The relationship is completely synergistic. They use each other to survive" Fischetti says. The bacteriophages help anthrax survive in the wild, in turn prolonging the existence of the viruses, which continue to shed from the infected earthworms. They are partners in crime.
The implications for biology are significant, Fischetti suggests. "It's not enough to sequence the genes of a bacteria to know what it does. You have to look at the phages as well."
Other researchers are catching on as well, looking at slightly different bugs. The viruses in the PloS One papers were "lysogenic," meaning they integrate their genes into their host's cells and reproduce when those cells reproduce. Another paper out this week, in the journal Science, led by Michael Vos of the United Kingdom's University of Oxford, to look at soil bacteriophages of the more common variety, called "lytic," that sneak into their host's genes, but churn out so many copies of themselves that they burst open host cells, destroying them.
In the Science study, Vos and colleagues show that lytic bacteriophages spark an evolutionary war of adaptation between viruses and bacteria. Lytic viruses within an inch of a bacteria in the soil will soon develop characteristics over a few generations that better enable their ability to infect bacteria which "suggests that phages are ahead of the bacteria in the co-evolutionary arms race."
Vos and colleagues suggest these deadly lytic bacteriophages must play a big role in the survival of bacteria, as well.
"In a sense they verify what we have found with anthrax," Fischetti says, "that these interactions occur at a significant level for most organisms in the soil. While they speculate that these interactions could play a role in bacterial survival, our data shows in detail how these interactions actually change the organism, anthrax in our case, for survival in the environment."
Most remarkably, the PloS One paper confirms a hypothesis first put forward by the pioneering scientists Louis Pasteur, who speculated 130 years ago that anthrax survives in earthworms. "We're really following in the footsteps of Pasteur," Schuch says. "Nobody thought to follow it up until now."