Training bacteria in stone conservation

Common soil bacteria could help protect ancient stone monuments and marble statues from corrosive pollution, scientists in Spain report. The research team's new germ-based technique "mimics what nature has been doing for eons" and promises to be inexpensive, geologist Carlos Rodriguez-Navarro of the University of Granada in Spain said. . .

In the past two decades, researchers suggested harnessing mineral-secreting germs as an environmentally friendly, low-maintenance art conservation workforce to harden rock. Most soil bacteria secrete calcium carbonate to help balance out internal body acidity.

Scientists previously tried using the common soil bacterium Bacillus cereus, which can cause vomiting or diarrhea if it contaminates food. Unfortunately, the calcium carbonate layer didn't cement the interior of the rock together, since it only penetrated a few microns deep -- approximately the width of a human blood cell. . .

The researchers then tried using another common soil bacterium, a harmless germ known as Myxococcus xanthus, which can glide en masse over surfaces and penetrate deep into the stone's pores. . .

Rodriquez-Navarro and a team of crystallographers and microbiologists experimented with a highly porous limestone often used in Granada's most outstanding yet crumbling landmarks. In findings appearing in the April issue of the journal Applied and Environmental Microbiology, the new cement their bacterial soup formed "is exceptionally hard, even harder than the original," Rodriquez-Navarro said. . .

X-rays and scanning electron microscopy revealed the crystal layers created by the new technique were as porous as the rock below them, and developed fast, mostly within five to 10 days. . .

The researchers are now in the process of implementing field-testing at selected buildings in Granada. Rodriquez-Navarro said his team also plans to see if the bacteria can be used to fill cracks in marble and protect non-chalky rocks such as granite and sandstone.

Posted by David on April 19, 2003 1:38 PM