Bacteria Genetically Engineered to Grow in Stripes

Scientists from California and Hong Kong genetically engineered bacterial cells so that they spontaneously grow in concentric rings. The number of rings can be controlled by altering expression of a single gene. They say the findings could shed light on the complex patterning that takes place during development.

“Natural systems make all kinds of wonderful patterns, but the problem is you never know what’s really controlling it,” said Terence Hwa, a professor of physics at the University of California, San Diego, and lead author on the study in a press release from the university. The research was published today in Science.

To create the bulls eye, researchers added genetic modules that sense how crowded the cells’ environment has become and respond by altering the bacterial cells’ movements.

One of the modules secretes a chemical signal called acyl-homoserine lactone (AHL). As the bacterial colony grows, AHL floods the accumulating cells, causing them to tumble in place rather than swim. Stuck in the agar of their dish, they pile up.

Because AHL doesn’t diffuse very far, a few cells escape and swim away to begin the process again.

Left to grow overnight, the cells create a target-like pattern of concentric rings of crowded and dispersed bacterial cells. By tweaking just one gene that limits how fast and far cells can swim, the researchers were able to control the number of rings the bacteria made. They can also manipulate the pattern by modifying how long AHL lasts before it degrades.