A whole more than the sum of its synthetic parts.

Synthetic biology is the realization of systems with desired behavior using biological materials. A recent addition to the field is a bipartite consortium of the bacterium Escherichia coli in which each species harbors complementary gene circuits that actuate only when both are present above a critical density. This bacterial "consensus" system, functional in liquid, solid, and biofilm niches, represents a novel strategy that raises the bar in terms of the specificity and complexity of tasks performed by engineered organisms.