Natural erosion, acid rain, and urban pollution are slowly turning some of the world's greatest monuments and buildings to dust. "The stone falls apart grain by grain because the binding agent is lost," says mineralogist Carlos Rodriguez-Navarro of the University of Granada in Spain. He has found a way to halt the damage, however, by enlisting bacteria to cement the grains back together.
Rodriguez-Navarro and his colleagues found that a common soil microbe, Myxococcus xanthus, pumps out crystals that mimic the way natural calcium carbonate binds together limestone, dolomite, and marble. The researchers put the bacteria to the test by placing pieces of limestone from the Granada cathedral inside a liquid broth containing the microbes. In two weeks, the bacteria infused the rock's surface with their crystalline glue. "Loose grains get reattached, and the whole structure is strengthened," Rodriguez-Navarro says. Equally important, the bacteria do not clog the rock's pores, which would hasten decomposition by trapping water inside—a problem with organic resins now used to protect stonework. Field tests, in which the buggy brew will either be sprayed on or wrapped around buildings as a poultice, could begin at the Granada cathedral and at the city's Royal Chapel within two years.
Grenada's 16th-century Royal Chapel—the burial spot of Spain's Catholic kings and queens—awaits aid from decay-fighting bacteria.Photograph courtesy of Carlos Rodriguez-Navarro/University of Granada.