Bacillus anthracis has a long history of interest to microbiologists.
It was the first organism used to prove Robert Koch's postulate: that an
organism could be isolated from a diseased animal, grown in the laboratory
and then used to infect a healthy animal, resulting in disease transmission.
Since Dr. Louis Pasteur performed these experiments in 1877, B. anthracis
has remained at the forefront of studies on pathogenic bacteria. The anthrax
bioterror attacks in the fall of 2001 that resulted in 5 deaths highlighted
the importance of the B. anthracis bacteria in bioterrorism.
Photo: Frederick C. Michel, ASM MicrobeLibrary
of the organism is due to the presence of two virulence plasmids, one of
which (pXO1) encodes a tripartite toxin which forms binary products of
lethal factor (LF) and protective antigen (PA) or edema factor (EF) and
protective antigen (PA). Collectively these binary toxins (LF/PA and EF/PA)
target multiple host functions, resulting in suppression of the immune
responses and eventually in death of the organism from a variety of
disrupted systems. The capsular polysaccharide (CPS) provides additional
protection against the host immune responses and genes for its production
are carried on the pXO2 plasmid. Ongoing studies are aimed at both
identifying the molecular mechanisms responsible for virulence and
potentially nullifying them or in producing a vaccine capable of
providing protection against the organism. Genomic comparison studies
can identify both the source of isolates used in the bioterror attacks
as well as understanding the evolution of the pathogen.
TIGR, who was done the bulk of genome sequencing for the B. anthracis and B. cereus organisms, was
the first to publish a B. anthracis genome in 2003 (
Nature. 2003 May 1;423(6935):81-6). This was for
the non-virulent Ames strain that lacks the two virulence plasmids. TIGR has
sequenced a fully virulent strain, Ames 0581, that contains both plasmids
and is considered the type strain for B. anthracis and the "gold standard" against which
all comparisons should be made. A number of other B. anthracis strains have been sequenced
by TIGR for comparison and have recently been released.
Assembly Archive recently created at NCBI links together trace data and finished sequence
providing complete information about a genome assembly. The Assembly Archive's first entries are a set
of closely related strains of Bacillus anthracis. The assemblies are avalaible at
A final remarkable find with regards to the related organism, Bacillus cereus,
has recently been published. B. anthracis is considered to be a member of the same
phylogenetic cluster as B. cereus, although B. cereus causes a much less severe disease than B. anthracis.
This difference is mainly attributable to the two toxin plasmids in B. anthracis. The WGS sequencing
of a new B. cereus strain G9241, was undertaken since this organism was found to cause an
anthrax-like disease in a patient (
Proc Natl Acad Sci USA. 2004 Jun 1;
101(22):8449-54). Two virulence plasmids, one almost identical to
pXO1 which contains the same toxin genes, and an analogous plasmid to pXO2, pBC218, that
presumably contains a polysaccharide capsule biosynthetic cluster that could produce a
extracellular polysaccharide capable of providing the same protection as the capsule encoded on pXO2 from B. anthracis.
This finding proves the close relationship of B. anthracis and B. cereus as well as
showing that the anthrax disease can be caused by an organism other than B. anthracis,
an important discovery that will be of vast interest to not only the micriobiological
and medical communities, but also the general public.
Global genome comparison of Bacillus anthracis