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[SANET-MG] superbug with anthrax genes
Superbug with Anthrax Genes
The Bacillus species causing anthrax and food poisoning are closely
related to each other and to a third, Bacillus thuringiensis, whose
toxin genes are extensively exploited to create genetically modified
Bt-crops. ISIS has warned of the potential for dangerous recombinants to
emerge; such a recombinant has now been identified. Dr. Mae-Wan Ho and
Prof. Joe Cummins caution against growing Bt crops, especially in the
A fully referenced version of this article is posted on ISIS Members’
website. Details here.
The three Bacillus bacteria all live in the soil and are so closely
related that they may as well be regarded as a single species. B.
anthracis, causes anthrax, B. cereus is linked to food poisoning, and B.
thuriengiensis is extensively exploited as biopesticides in genetically
engineered Bt crops, now widely cultivated in the United States, and
increasingly being promoted in Third World countries. The three bacteria
readily mate with one another and exchange plasmids (circular pieces of
DNA) carrying specific toxin and virulence genes. They share very
similar viruses (phages) that can integrate into the bacterial genome as
‘prophage’, and can hence also move toxin and virulence genes among
them, many of them reside in the bacterial chromosome. Cummins has
warned that dangerous recombinants could arise, from gene exchange
between the bacteria and between the Bt plant debris and bacteria in the
Now, an international team of infectious disease researchers led by
Claire M. Fraser of the Centers for Disease Control and Prevention (CDC)
in Atlanta, Georgia, USA, have identified a recombinant between B.
anthracis and B. cereus. They were alerted last year when two hospital
patients in Texas died of severe pneumonia that appeared to be caused by
inhalation anthrax, but neither patient was infected with B. anthracis.
Instead, DNA tests showed that both patients were infected by a strain
of B. cereus that normally causes mild food poisoning, which has somehow
acquired the lethal anthrax genes.
When the Texas cases came to light, the CDC scientists were sequencing a
strain of B. cereus isolated from a man in Louisiana who, in 1994,
showed up with severe anthrax-like symptoms. The Texas and Lousiana
patients were all metal workers who seemed to have inhaled the bacteria.
Anthrax is an acute fatal disease among mammals and B. anthracis became
widely known as a biological weapon soon after September 11, 2001. It
has two plasmids: pXO1 carrying the lethal toxin complex (edema factor,
lethal factor and protective antigen), and pXO2 carrying the glutamic
acid polymer that inhibits white blood cells from engulfing and
digesting the bacterium. Until a few years ago, B. anthracis was thought
to be distinct from B. cereus, because they look different and causes
The researchers sequenced the B. cereus genome using draft genome
sequences obtained and assembled by the company Celera, and the
resulting sequence annotated through The Institute for Genomic Research
(TIGR) Bioinformatics pipeline, set up by Craig Venter, the maverick
scientist who founded Celera to sequence the human genome, succeeded
only too well, and was sacked from the company in January 2002, after he
remarked on there being too few genes to support the simplistic idea
that organisms are hardwired in their genes.
It turns out that the culprit strain of B. cereus G9241 had acquired a
plasmid very similar to the pXO1 of B. anthracis. In addition, analysis
of seven other metabolic genes showed that the strain is closely related
to, albeit distinct from B. anthracis.
The sequence of B. cereus G9241 genome reveals a mosaic structure, which
could be due to the presence of a great number of what appears to be
known and novel mobile genetic elements that can insert sequences from
other sources. It also has a 119 110bp circular plasmid with high
similarity to B. anthracis pXO1. There is, further, a cryptic phage of
29 886bp that encodes phage-like proteins and a plasmid replicon
(replicating unit) similar to B. anthracis plasmid pXO2. It also carries
genes that, if functional, should provide the strain with resistance to
b-lactam, chloramphenicol and macrolide antimicrobial agents.
When injected into mice, B. cereus G9241 proved to be 100% lethal, as
was B. anthracis, but it killed the mice almost twice as fast. All the
mice injected with an ordinary B. cereus strain survived the experiment.
As a result of these findings, the researchers concluded that, “it may
not be appropriate to consider B. anthracis, as currently defined, as
the only species capable of causing inhalation anthrax-like disease.”
Another noteworthy feature is that at least two isolates of B. cereus
(ATCC 14579) and M 1550) are extremely closely related to and cluster
with B. thuringiensis. A number of delta endotoxins from B.
thuringiensis strains are implicated in allergies and other illnesses,
or known to be immunogenic. What sort of disease agent might emerge from
B. cereus if it acquired endotoxin genes either from B. thuringiensis or
from Bt crop debris in the soil? This question is especially pertinent
in view of the substantial changes in the genetically modified Bt genes
that are completely untested and hence unknown in toxicities.
Countries, especially those in the Third World, where farmers live next
to their fields, should be particularly wary about growing Bt crops.
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