Schuch says that two of the ways that scientists could look for anthrax in these areas would be to use polymerase chain reaction or antibodies that recognize anthrax. As opposed to heating the soil, both of these methods would detect anthrax growing there. Following up on Schuch's idea to look for the bacteria not just in the soil but also in earthworms would be as simple as squeezing out the intestinal contents, as Schuch does, and letting the bacteria in the mix grow on a Petri dish. Anthracis would reveal itself because the bacterial cells grow as characteristic flat and colorless colonies, Schuch says.
Unfortunately, methods to prevent anthracis from persisting and causing disease are not so straightforward. "I don't know if we know enough yet about how to control these [phages]," Fischetti says. Among the next steps, he plans to examine if the phages that he and Schuch discovered influence bacterial genes that are involved in infecting mammals.
New phage frontier
Schuch and Fischetti have no reason to think that the eight phages they discovered complete the inventory of anthracis viruses. Fischetti estimates that there are one million bacteria in one gram of soil, and 10 times more phages. He suspects that other phages infect anthracis and probably have additional roles such as controlling the disease's virulence. "Phages may be doing more for bacterial survival on Earth than we thought," he says. "I think they are in control."
The new anthracis phages probably originated in related Bacillus bacteria because, as Schuch points out, these cousins of anthracis are more widespread in soil and earthworm intestines. But, combined with anthracis's particular genome that harbors disease-causing genes, these phage genes have unique effects, such as inducing expression of growth and biofilm formation.
"The remarkable thing about phages is that they expand the genetic diversity of the host that they infect," says Anca Segall, a phage biologist at San Diego State University. Segall, who calls Schuch and Fischetti's work to uncover the role of new anthracis phages "absolutely spectacular," started sequencing the DNA of phages from marine Bacilli several years ago. Some of the viruses she found induce the aquatic bacteria to sporulate.
Fischetti suspects that efforts to sequence the bacteria in the human gut, which are currently underway, will also reveal that phages control this diverse microcosm.
As the researchers work to understand the interplay between anthracis and phages, Schuch says that they will still be on the lookout for phage genes with anti-anthrax properties. It is possible that some of their eight new viruses contain genes that, when activated, kill the bacteria. In earlier work, Fischetti's team found a phage gene that encodes an enzyme that destroys anthracis cell walls. It is currently in development as a clinical therapy. "It's envisioned mostly as a treatment—as a replacement for or an adjunct to antibiotics—in people who have been exposed to [antibiotic-resistant] anthrax strains," Schuch says. "It might be better to use mixtures rather than single enzymes, just because then you'd be sure to kill every strain."