How bacteria create flower art
When sticky bacteria meet roaming bacteria in a petri dish, friction between the two can cause flower patterns to blossom. Escherichia coli bacteria growing on a Jello-like substance called agar tend to stick to the surface, and colonies of the microbes don’t spread very far. But colonies of Acinetobacter baylyi expand in rapidly growing circles as the bacteria crawl on hairlike pili over the agar’s surface. Neither type of microbe is very exciting to look at on its own, says Lev Tsimring, a theoretical physicist at the University of California, San Diego. But “when we mixed them together, we saw these absolutely mind-blowing structures growing.” Physical interactions between the two types of bacteria create floral patterns, he and colleagues found. Mobile A. baylyi “pushes E. coli in front it, sort of like a snowplow,” Tsimring says. But sticky E. coli dig in their heels, holding back a wave of A. baylyi like an elastic band wrapped around a balloon, he says. In some places...