Good guys and bad guys share tactics

Both members of a microbial odd couple—the brucellosis pathogen and a symbiotic bacterium in plants—depend on the same gene to settle into their hosts.

The discovery raises hopes for a vaccine to protect people from brucellosis, say Kristin LeVier of the Massachusetts Institute of Technology and her colleagues in the March 31 Science.

The hard-to-treat disease wracks people with fever and causes abortion in livestock. Vigilance has nearly stamped out U.S. cases, except among Yellowstone bison and elk. However, brucellosis still troubles other countries.

At the other end of the usefulness spectrum, Rhizobium meliloti settles into nodules on legume roots and converts atmospheric nitrogen into the form that plants need.

Earlier work showed that R. meliloti invades cells but can’t establish itself without the bacA gene. LeVier and her colleagues found that Brucella abortus with defective bacA enters mouse cells but can’t create a chronic infection.

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.