Sticking together makes bacteria nearly invincible

Bacterial life is astonishingly varied. These single-celled organisms come as spheres, rods, spirals and corkscrews. A few are a centimetre long; most are tens of thousands of times smaller. They have been found on Mount Everest, in Antarctica, and deep within Earth’s crust. And yet virtually every bacterial species ever found shares one trait: its members do not like living alone.

Matthew Fields, a microbiologist at Montana State University, reckons that most of the bacteria living on the planet exist in colonies. Known as biofilms, these slimy aggregates are held together by strands of DNA, proteins and other molecules recycled from the cells of dead neighbours. Such sociability is ancient. Some of the oldest known evidence of life on Earth are fossilised biofilms known as stromatolites. A group of stromatolites in Western Australia are thought to be 3.5bn years old.