The bacterium that causes anthrax, Bacillus anthracis, is a quiet little spore — until it gets into a mammal. Then it produces a host-killing toxin and self-protecting capsules in response to higher bicarbonate levels than normally occur in the environment. How it recognizes this compound was the subject of a recent study by Marta Perego and her colleagues at the Scripps Research Institute in La Jolla, California.
They searched the literature for other organisms that use bicarbonate, and found work on a photosynthetic bacterium, Synechococcus elongatus. This shuttles bicarbonate through its cell membrane by means of a multiprotein structure known as an ABC transporter. A scan of B. anthracis' genome for genes that encode similar proteins pinpointed a section named BAS2714–12. Deleting this region rendered the pathogen harmless to mice.