Big cat eats human… and acquires new pathogen?

About half of all humans harbor Helicobacter pylori in their stomachs — this bacterium can cause stomach ulcers, gastritis and gastric cancer. H. acinonychis, a close relative of H. pylori, colonizes the stomachs of several big cats — cheetah, tiger and lion.

Now Stephan C. Schuster, Mark Achtman from the Max-Planck Institute for Infectious Biology (Berlin, Germany), and colleagues have sequenced the genomes of this feline Helicobacter species to answer the question of "Who ate whom?" In other words, did H. pylori evolve from an ancestral H. acinonychis that jumped from cats to humans, or vice versa?

The researchers found that while the two genomes are generally extremely similar, the H. acinonychis genome contains fragmented (non-functional) versions of numerous H. pylori genes. Interestingly, many of these genes encode outer membrane proteins that might provoke an immune response. What's more, only a handful of genes are specific to H. acinonychis, but five of these are likely to help the bacterium evade host immune defenses.

The researchers conclude that within the last 200,000 years a big cat ate an early human infected with H. pylori — and some of the H. pylori made it past the cat's immune defenses to start on its evolutionary journey of becoming H. acinonychis.