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January 27, 2015

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Anthrax faces silent war with giant, deadly virus

Jan. 27, 2014
Courtesy of University of California - Davis
and World Science staff

Al­though the an­thrax bac­te­ri­um strikes fear in the hearts of many, it has its own mor­tal en­e­my—a huge, deadly vi­rus, re­search­ers have found.

Sci­en­tists are hop­ing the vi­rus could help lead to an ef­fec­tive treat­ment against an­thrax and some re­lat­ed pathogens that cause food poi­son­ing. In­ves­ti­ga­tors have al­so been look­ing for such new treat­ments be­cause an­ti­bi­otics don’t work as well as they used to—bac­te­ria are evolv­ing coun­ter­mea­sures, or re­sist­ance.

The Tsam­sa vir­us. The scale bar at low­er left is one ten-thou­sandths of a mil­li­meter. (Cre­dit: Jo­chen Klumpp, ETH Zur­ich, Swit­zer­land)


In­ves­ti­ga­tors un­cov­ered the an­ti-an­thrax vi­rus, called a bac­te­ri­o­phage, in ze­bras that had died from an­thrax in Etosha Na­t­ional Park, Na­mib­ia. The re­search is pub­lished Jan. 27 in the jour­nal PLoS One.

The an­thrax bac­te­ri­um, Ba­cil­lus an­thra­cis, forms spores that sur­vive in soil for a long time. Ze­bras are in­fected when they pick up the spores while graz­ing; the bac­te­ria mul­ti­ply and when the an­i­mal dies, they form spores that re­turn to the soil.

While the bac­te­ri­um in­vades and kills the an­i­mal, bac­te­ri­o­phages, lit­er­ally “bac­te­ria eaters,” are vi­ruses that in­vade and kill bac­te­ria, the sci­en­tists ex­plained. 

The first thing the team no­ticed was that the vi­rus was a vo­ra­cious pred­a­tor of the an­thrax bac­te­ri­um, said Holly Ganz, a re­search sci­ent­ist at the Uni­vers­ity of Cal­i­for­nia, Da­vis Ge­nome Cen­ter and co-author of the pa­per. They al­so no­ticed the vi­rus, named Ba­cil­lus phage Tsamsa, is one of the larg­est known bac­te­ri­o­phages, with a gi­ant head, a long tail and a large ge­nome.

zebras graze in Eto­sha Nat­ion­al Park, Nam­i­bia. (Cre­dit: Holly Ganz, UC Da­vis)


Tsamsa in­fects not only B. an­thracis but al­so some closely re­lat­ed bac­te­ria, in­clud­ing strains of Ba­cil­lus ce­re­us, which can cause food poi­son­ing, the in­ves­ti­ga­tors added. De­cod­ing the ge­nome let re­search­ers iden­ti­fy the gene for ly­sin, a com­pound the vi­rus uses to kill bac­te­ri­al cells, they said. That it­self has po­ten­tial use as an an­ti­bi­ot­ic or dis­in­fect­ing agent.

Bac­te­rio­phages are of­ten highly spe­cif­ic to one strain of bac­te­ria, and when they were first discov­ered in the early 20th cen­tu­ry there was strong in­ter­est in them as an­ti­mi­cro­bi­al agents. But the dis­cov­ery of pen­i­cil­lin and oth­er an­ti­bi­otics eclipsed phage treat­ments in the West. “With grow­ing con­cerns about an­ti­bi­ot­ic re­sist­ance and su­per­bugs, peo­ple are com­ing back to look at phages,” said Ganz.


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Although the anthrax bacterium strikes fear in the hearts of many, it has its own mortal enemy—a huge, deadly virus, researchers have found. Scientists are hoping the virus could help lead to an effective treatment against anthrax and some related pathogens that cause food poisoning. Investigators have also been looking for such new treatments because antibiotics don’t work as well as they used to—bacteria are evolving countermeasures, or resistance. Investigators uncovered the unusually large anti-anthrax virus, called a bacteriophage, in zebras that had died from anthrax in Etosha National Park, Namibia. The research is published Jan. 27 in the journal PLoS One. The anthrax bacterium, Bacillus anthracis, forms spores that survive in soil for a long time. Zebras are infected when they pick up the spores while grazing; the bacteria multiply and when the animal dies, they form spores that return to the soil as the carcass decomposes. While the bacterium invades and kills the animal, bacteriophages, literally “bacteria eaters,” are viruses that invade and kill bacteria, the scientists explained. The first thing the team noticed was that the virus was a voracious predator of the anthrax bacterium, said Holly Ganz, a research scientist at the University of California, Davis Genome Center and co-author of the paper. They also noticed the virus, named Bacillus phage Tsamsa, is one of the largest known bacteriophages, with a giant head, a long tail and a large genome. Tsamsa infects not only B. anthracis but also some closely related bacteria, including strains of Bacillus cereus, which can cause food poisoning, the investigators added. Decoding the genome let researchers identify the gene for lysin, a compound the virus uses to kill bacterial cells, they said. That itself has potential use as an antibiotic or disinfecting agent. Bacteriophages are often highly specific to a particular strain of bacteria, and when they were first discovered in the early 20th century there was strong interest in them as antimicrobial agents. But the discovery of penicillin and other antibiotics eclipsed phage treatments in the West. “With growing concerns about antibiotic resistance and superbugs, people are coming back to look at phages,” said Ganz.