Significance of the discovery of anthrax toxin genes in a naturally occurring microbe other than Bacillus anthracis

"Nature itself is the most capable creator of new biothreat agents," says Dr. Claire M. Fraser, president of The Institute of Genomic Research (TIGR), one of the world's leading genomics research centers. She should know, since she is a senior scientist in the discovery, reported earlier this June, of a newly identified strain of the soil microbe Bacillus cereus containing anthrax toxin genes. The B. cereus bacterium is most commonly associated with food poisoning, although it also has been suspected to be the cause of some cases of fatal respiratory disease.

At the annual meeting of the American Society for Biochemistry and Molecular Biology (ASBMB)/8th International Union of Biochemistry and Molecular Biology Conference (IUBMB) in Boston, Dr. Fraser discusses, for the first time, the significance of the discovery of anthrax toxin genes in a naturally occurring microbe other than Bacillus anthracis, the bacterium that causes anthrax. She also discusses how this discovery fits into the ongoing debate about how to deal with potential new biothreat agents.

The study, conducted with collaborators at the Centers for Disease Control and Prevention (CDC), found the anthrax toxin genes in a virulent strain of the soil bacterium Bacillus cereus that was isolated from a patient who was suffering from a pneumonia similar to inhalation anthrax. It is not yet known exactly how the anthrax toxin genes ended up in the B. cereus isolate, but the process is assumed to have been a natural one.

The discovery was first reported in the June 1, 2004 issue of the Proceedings of the National Academy of Sciences (PNAS). The ASBMB meeting will be the first public forum in which Dr. Fraser will discuss the paper, of which she is senior author.

At the ASBMB presentation, Dr. Fraser will discuss the B. cereus study in the wider context of the comparative genomics of this family of bacteria and offer insights into the physiology and evolution of anthrax and its close relatives, based partly on TIGR's sequencing of numerous strains of the pathogens.

Using both DNA sequence analysis and comparative genome hybridization of more than 20 strains within this family of organisms, she and her colleagues found many similarities of genes and chromosomes, including several chromosome-encoded proteins that may help explain why these bacteria are pathogenic and also may identify important targets for vaccines and drugs. But the genome analysis also revealed important differences within this group of organisms. The large plasmids (small DNA structures outside the cell's chromosome) are highly variable among the bacteria strains, suggesting considerable mobility of key toxin genes.

Dr. Fraser also will discuss what this means to the nation's effort to catalog potential biothreat agents and to develop better ways to identify them quickly. "These data further highlight the challenges in the laboratory and clinical differential diagnosis and response to naturally occurring pathogens that may resemble known bioterror agents," says Dr. Fraser. She says the TIGR/CDC study also shows how genomics can rapidly assist public health experts in responding not only to clearly identified biothreat agents, but also to novel pathogens with similar potential.