A real-life game of life

Posted November 17, 2005

The classic Conway game of life is a wonderful cellular automaton exhibiting really fascinating behavior derived from very simple rules, governing how a "cell" will live, die, or reproduce depending on the number of its neighbors. This is just a simulation, using a grid of points that can be on or off.

At a talk on synthetic biology today, I was introduced to a realization of this (PDF) using actual living cells. The researchers genetically-engineered bacteria such that they would secrete and detect chemicals indicating their presence. If a bacterium sees it is living in a comfortable density of other bacteria, then everything is fine and it grows and reproduces. If it sees that it is too lonely, or too crowded, then a feedback mechanism involving this chemical is triggered, and it commits suicide.

The speaker showed a video of this. Cells growing, growing, and then <pop-pop-pop> they get too crowded and the built-in cellular death mechanism goes off, causing the bacteria to just disintegrate instantaneously on the time-scale of the film. I wish I could find this video to link to, but I can't see it on the web anywhere. The net result is that the population of bacteria self-regulates its density as the colony grows, maintaining a preprogrammed "optimal" level of crowding.

My reaction to this is very odd. On the one hand, I really shouldn't care, since every day I kill millions of bacteria without a passing thought (and my body no doubt provides a happy home to millions more), to say nothing of the number of my own cells that die each day, on purpose or otherwise. On the other hand, it struck me as somehow obscene to engineer an organism to kill itself on purpose for no "good" reason.

No doubt this is just the tip of the iceberg with regard to ethical issues surrounding genetic engineering, but it's a fascinating case study in what is possible now and what we should be thinking about.