Dobzhansky and anthrax

The Washington Post today reminds us that there has been little progress in uncovering the source of the 2001 anthrax attacks. [1]

First, a disclaimer. I'm not an "evolutionary biologist," per se. I have what is I swear the longest job title ever--molecular infectious disease epidemiologist. As such, I often get asked, "what's the relevance of evolution to your work?" Or, I'll read editorials such as Dr. Skell's recently in The Scientist [2] questioning the use of evolutionary theory in experimental biology, and be disheartened. Yet the method of investigating the anthrax attacks shows once again just how relevant evolutionary theory is to all areas of biology, and how Dobzhansky's famous "Nothing makes sense..." comment once again ring true.

There are several clues regarding the 2001 attack (for those unfamiliar with the story, the background can be found here) [3]. Some are in the packaging of the material: the writing on the envelope, the location of the postmark, the mailbox where the letters were dropped. Others are in the processing of the anthrax: the spores were finely milled, so as to be more easily aerosolized. Finally, there are clues in the bacteria themselves: in their genetic makeup. Early on, they looked at the molecular profiles of the anthrax and compared them to known strains, zeroing in on the Ames anthrax strain.

This is a good thing, because the Ames strain is fairly rare in nature--making it more likely that the anthrax was obtained from a laboratory. The problem with anthrax, however, is that as a species, it is very homogeneous: there isn't a lot of variation in the DNA sequence. Fingerprinting techniques like pulse field gel electrophoresis (PFGE), which uses restriction enzymes to cut the bacterial chromosome into smaller pieces to be run out on agarose gels, work well for pathogens like E. coli and Staphylococcus aureus, but isn't nearly as useful in anthrax due to the low level of sequence diversity. This makes it necessary to use more sensitive techniques to identify the bacterium, bringing us back to the characterization of the 2001 bioterrorist strain as the Ames anthrax strain.

What is the "Ames strain," exactly? In a 2001 Science article [4], it was noted that

Over the past 2 decades, the U.S. Army Medical Research Institute of Infectious Diseases [USAMRIID] in Fort Detrick, Maryland, sent the Ames strain to several research labs. And as it was passed around and grown in different labs, it may well have accumulated minute new changes.

Researcher Martin Hugh-Jones noted, "The Ames strain can be many different things. A very detailed fingerprint could reveal very very minor variations."

Therefore, it's the accumulation of these mutations--from a common ancestor, the original "Ames strain" (sound familiar?)--that may allow for a more specific determination of the origin of the 2001 strain, shedding light on the most notable biocrime in recent history. I've not seen a published comparison of the whole genome sequences of the various Ames strains, but that seems like the logical way to proceed in this (apparently stalled) investigation--go right back to that "useless" evolutionary biology to save the day.


[1] Lengel, A. "Little progress in FBI probe of anthrax attacks." Washington Post. September 16, 2005.
[2] Skell, PS. 2005. "Why do we invoke Darwin? Evolutionary theory contributes little to experimental biology." The Scientist. 19:10.
[4] Enserink, M. 2001. "Taking anthrax's genetic fingerprints." Science: 294; 1810-2.

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