MADISON – Eight hundred years ago, in a hardscrabble farming community on the outskirts of what was once one of the fabled cities of the ancient world, Troy, a 30-year-old woman was laid to rest in a stone-lined grave.
Like others in the Byzantine era graveyard, the woman’s bones bore the unmistakable signs of a hard agrarian existence. But something else caught the attention of Henrike Kiesewetter, an archaeologist affiliated with Project Troia at Tüebingen University, as she curated the skeleton: two calcified nodules, each the size of a strawberry, nestled at the base of the chest, just below the ribs.
“The preliminary thought was that these were tubercles arising from tuberculosis,” says Caitlin Pepperell, a University of Wisconsin-Madison expert on the evolution of pathogens and a professor of medicine and medical microbiology. A bacterial infection, tuberculosis is characterized, often, by the growth of calcified nodules in the lungs or other tissues. DNA, elemental and microscopic analysis of the round white stones, however, ruled out tuberculosis as well as urinary or kidney stones as possibilities.
Cracking open the nodules, researchers discovered extraordinarily well preserved microfossils, mineralized ‘ghost cells,’ that closely resembled bacteria from the genus Staphylococcus, a family that includes the highly pathogenic species S. aureus.
The nodules and the DNA locked inside their concentric layers of calcium were sent to McMaster University’s Hendrik Poinar, an expert in ancient DNA whose lab is known for its prowess in extracting and reconstructing genetic material from ancient archaeological and paleontological remains.
“Amazingly, these samples yielded enough DNA to fully reconstruct the genomes of two species of bacteria, Staphylococcus saprophyticus and Gardnerella vaginalis, which infected the woman and likely led to her death,” says Poinar.
Writing this week (Jan. 10, 2017) in the journal eLife, a team led by Pepperell and Poinar provides a molecular portrait of the fatal infection. The work lends insight into the everyday hazards of life in the late Byzantine Empire, sometime around the early 13th century, as well as the evolution of Staphylococcus saprophyticus, a common bacterial pathogen.