Guardian angels


By Rakesh Kalshian THE magnificent natural sandstone sculptures of Utah and Arizona may owe their continued existence to some microscopic conservationists. Microbiologist Harry Kurtz and geologist Dennis Netoff of the Sam Houston State University in Huntsville, Texas, have discovered that sandstone contains communities of photosynthetic cyanobacteria. These protect friable sandstone from the ravages of rain and wind, the researchers believe. They hope the cyanobacteria can be cultivated to help preserve damaged hiking trails. The researchers took samples of crushed sandstone and added a solution containing bicarbonate, to give the microorganisms a source of a carbon. After three months, the sand turned distinctly green, showing that a thriving community of cyanobacteria had grown up. More importantly, the sand grains had coalesced into a hardened mass. “And you could feel that the surface was harder where it was greener,” says Kurtz. Further analysis revealed that the cyanobacteria were making acidic polysaccharides, starches that can bind to metal ions to produce a tough matrix. Kurtz thinks that the same process happens in natural sandstone, which often has a rippled surface. “You can see the ridges are greener than the depressions,” he says. “The cyanobacteria colonise the ridges, making them harder to erode.” In the arid western US, the formation of the protective matrix is presumably limited by the availability of water, which frees metal ions from the rock. But Kurtz and Netoff believe that damaged sandstone could be preserved by spraying it with water spiked with the necessary metal ions. More on these topics:
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