Web Extras: Article

Engineering an Ecosystem
By Erin Fults
Posted July 9, 2008

When you hear the words "predator" and "prey," you probably imagine a cat stalking a mouse or a lion chasing a wildebeest. But new research is unveiling predator-prey interactions in a place much smaller than the Serengeti—a petri dish. And while the bacteria in that dish aren't actually eating each other, they are following a similar model of population control.

Although initially placed in different locations and in equal numbers on this petri dish, predator cells (green) now overtake prey cells (red) due to their release of a chemical that triggered the death of prey cells. Credit: Hao Song

Bioengineers Lingchong You and Frances Arnold developed an artificial ecosystem made up of two bacterial populations to see if complex interactions found in larger ecosystems could be created in simpler organisms. They programmed a new gene circuit into the bacteria that acted as additional software, which You says, "coaxed the cells to do what we wanted them to do."

The researchers programmed the bacteria to be either "predator" or "prey" cells. In this shared ecosystem, the predator cells released a chemical signal that activated a suicide gene in the subservient cells and caused their self-destruction. The prey cells released a different chemical signal that kept the predator cells from killing themselves. The two populations appeared to oscillate in their levels, just like natural predator-prey ecosystems.

You, now at Duke University, began looking for ways to reprogram bacterial cells while he was a post-doc in Arnold's lab at the California Institute of Technology. He was interested in getting the bacterial cells to act in a certain way according to instructions he would encode in their genes. This sort of science is called synthetic biology, which uses our understanding of natural systems, like animal interactions in the wild, to build artificial ones in bacteria and other organisms.

"It was very interesting to me in the sense that you have this power to program a cell by designing some sort of gene circuit," says You.

Prey cells (red) are forced to the center of the plate when predator cells (green) are initially placed at four points around the petri dish. Credit: Hao Song

With terms like circuits and reprogramming, you may be thinking of computers rather than living organisms. But You says that looking at cells in terms of computers can be a good thing.

"The synthetic ecosystem has the advantage in that we can manipulate it experimentally in an easier fashion than large-scale ecological systems," says You. "So the idea is that we can simplify the cell as if it were a computer and then insert some additional 'software.'"

Arnold isn't so quick to consider cells as mini-computers and says, "Some things are just so complex that we don't know how to write the software." But, both researchers agree that the bacteria can act as good experimental models to help others design and explore different natural systems that lead to greater insights on the behavior of complex ecosystems.

New applications are just waiting to be discovered. And Arnold says, "The future of biological engineering is limited only by your imagination."