A type of living concrete made from bacteria could one day help to reduce the environmental impact of the construction industry.

Wil Srubar at the University of Colorado Boulder and his colleagues have used a type of bacteria, Synechococcus, to create building blocks in a variety of shapes.

The team combined the bacteria with gelatin, sand and nutrients in a liquid mixture, then placed this in a mould. With heat and sunlight, the bacteria produced calcium carbonate crystals around the sand particles, in a process similar to how seashells form in the ocean.

When cooled, the gelatin solidified the mixture into a gel form. The team then dehydrated the gel to toughen it, with the entire process taking several hours.

The team liken their living material to concrete, which is a mixture of gravel and sand and cement combined with water. But its mechanical properties are more similar to mortar, a weaker material usually made with cement and sand and found between the bricks of buildings, says Srubar. It isn’t yet as strong as regular bricks.

An advantage of using bacteria to create the concrete is that if they aren’t dehydrated entirely, they continue to grow. One brick can be split to create two bricks with some additional sand and nutrient solution. The team showed that one brick could yield up to eight in total after several divisions.

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