Cracks in concrete surfaces make them vulnerable, allowing water and tag-along aggressive chemicals in, says Henk Jonkers of Delft University of Technology in the Netherlands.

Patching cracks in old concrete is a time-consuming business, and rebuilding concrete structures is expensive. Jonkers thinks the answer is to fight nature with nature by packing the concrete with bacteria that use water and calcium lactate "food" to make calcite, a natural cement, NewScientist.com reported Wednesday.

Most organisms can't survive in a pH above 10, typical of concrete. To find bacteria that are happy in such an alkaline environment, Jonkers and his colleagues looked to soda lakes in Russia and Egypt, where the pH of the water is naturally high, and found strains of Bacillus thriving there.

Bacteria can take on a dormant spore state for long periods -- up to 50 years -- without food or water. Jonkers compares them to seeds waiting for water to germinate.

When water starts to seep into a hairline crack, Jonkers says, the bacteria would activate and begin to consume calcium. As they fed, they would combine the calcium with oxygen and carbon dioxide to form calcite -- essentially pure limestone.

Jonkers presented his work at the EU-U.S. Frontiers of Engineering symposium in Cambridge, England.

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