Concrete is incredibly tough under pressure – that’s why it’s so critical in buildings and roads. But it’s not so strong under tension – you can pull it apart much easier than you can crush it, which leads to cracks in concrete that sees a lot of temperature changes and/or heavy use. Steel rebar is used to reinforce the stuff and make it last longer, but the cracks still appear and grow over time.
Enter a calcium carbonate-producing bacteria. Dormant spores, along with some bacteria food, were mixed into concrete. When the resulting block was cracked, the bacteria woke up because of the newly-available oxygen from the air and started producing calcium carbonate (which is what makes up limestone), repairing the crack. Once the crack had closed up, the bacteria went back into hibernation mode. Clever, right? It wouldn’t last forever, of course, but it could still extend the lifetime of concrete in a number of applications.